Class 10 Science Chapter 9 HEREDITY: Genes, Traits and Inheritance

Meta Description: In this article, we delve into the intricacies of Class 10 Science Chapter 9 HEREDITY, exploring topics such as genes, traits and inheritance to help you gain a better understanding of this essential scientific concept.

Class 10 Science Chapter 9 HEREDITY is an essential topic that lays the foundation for the study of genetics. HEREDITY refers to the passing down of traits from parents to their offspring, which is what makes every individual unique. Understanding this concept is crucial not just for science students, but for anyone interested in learning more about the science behind genetics.

In this article, we will delve into the key concepts of Class 10 Science Chapter 9 HEREDITY, exploring the fundamental principles of genes, traits, and inheritance. By the end of this article, you will have a better understanding of this fascinating topic and the role it plays in shaping who we are.

Headings:

1. Genes and Traits: An Overview
2. Understanding the Role of DNA
3. Mendel’s Laws of Inheritance
4. Dominant and Recessive Traits
5. Pedigree Analysis: Tracing Inheritance Patterns
6. Genetic Disorders: An Overview
7. Applications of Genetic Engineering
8. Frequently Asked Questions about HEREDITY
9. Conclusion

Sub-Headings:

1. Genes and Traits: An Overview
   • The Definition of Genes and Traits

Genes are segments of DNA that contain the instructions for building and maintaining an organism. They are the basic units of heredity and determine many of an organism’s characteristics, such as eye color, height, and susceptibility to certain diseases.

Traits, on the other hand, are the observable characteristics or features of an organism that are influenced by genes as well as environmental factors. These can include physical traits like eye color and hair texture, as well as behavioral traits like temperament and intelligence.

In summary, genes provide the instructions for building and maintaining an organism, while traits are the observable characteristics that result from the interaction of genes and the environment.

• • Types of Traits

There are various types of traits, including:

1. Physical traits: These are observable characteristics of an organism’s physical appearance, such as eye color, height, and hair texture.
2. Behavioral traits: These are observable patterns of an organism’s behavior, such as temperament, intelligence, and social tendencies.
3. Inherited traits: These are traits that are passed down from parent to offspring through genes.
4. Acquired traits: These are traits that an organism develops over its lifetime through experiences or exposure to certain environmental factors.
5. Dominant traits: These are traits that are expressed when an individual has one or two copies of a dominant allele.
6. Recessive traits: These are traits that are only expressed when an individual has two copies of a recessive allele.
7. Polygenic traits: These are traits that are influenced by multiple genes, such as height and skin color.
8. Multifactorial traits: These are traits that are influenced by both genetic and environmental factors, such as intelligence and susceptibility to certain diseases.

Understanding these different types of traits is important in fields such as genetics, biology, and psychology, as it can help researchers to better understand how traits are passed down from generation to generation and how they are influenced by various factors.

• • Chromosomes and Genes

Chromosomes and genes are two closely related concepts in genetics.

Chromosomes are long, thread-like structures made up of DNA molecules and associated proteins. They are found in the nucleus of cells and carry the genetic information that is passed from parent to offspring. Humans have 23 pairs of chromosomes, for a total of 46 chromosomes in each cell.

Genes are segments of DNA that are located on chromosomes. They provide the instructions for building and maintaining an organism, such as the production of proteins that carry out various functions in the body. Genes determine many of an organism’s characteristics, such as eye color, height, and susceptibility to certain diseases.

Each chromosome contains many genes, and the specific combination of genes on each chromosome determines an organism’s traits. For example, a gene for brown eyes may be located on chromosome 15, and a gene for tall height may be located on chromosome 7.

During sexual reproduction, the chromosomes from each parent combine to form a unique set of genes in the offspring. This process is known as genetic recombination and contributes to the genetic diversity within a population.

In summary, chromosomes are the structures that contain an organism’s genetic information, while genes are the segments of DNA that provide the instructions for building and maintaining an organism. Understanding the relationship between chromosomes and genes is important for understanding the mechanisms of heredity and genetic diversity.

1. Understanding the Role of DNA
   • The Structure of DNA

DNA, or deoxyribonucleic acid, is a molecule that carries genetic information and is found in the cells of all living organisms. It has a complex, double-helical structure that is made up of four types of nucleotides: adenine (A), thymine (T), cytosine (C), and guanine (G).

The nucleotides are arranged in pairs, with A always pairing with T and C always pairing with G, through hydrogen bonds. These pairs form the “rungs” of the DNA ladder, while the sugar and phosphate molecules make up the “backbone” of the ladder. The specific sequence of nucleotides along the DNA molecule determines the genetic information that is encoded in the DNA.

The double helix of DNA is held together by a combination of hydrogen bonds, van der Waals forces, and hydrophobic interactions. The helix structure allows the DNA molecule to be tightly packed into the nucleus of a cell, while also allowing for the easy unwinding of the molecule during processes such as DNA replication and transcription.

Understanding the structure of DNA is important for understanding how genetic information is stored, transmitted, and expressed in living organisms. It has also led to many important advances in fields such as medicine, agriculture, and biotechnology.

• • DNA Replication

DNA replication is the process by which a cell makes an exact copy of its DNA before cell division. This ensures that each new cell will have a complete set of genetic information.

The process of DNA replication begins with the unwinding of the double helix structure of the DNA molecule by the enzyme helicase. This creates a replication fork, which is the point where the DNA molecule is being separated into two single strands.

The next step involves the enzyme primase adding short RNA primers to the template strand, which provide a starting point for DNA polymerase to begin adding nucleotides. DNA polymerase then adds nucleotides to the new strand, following the complementary base pairing rules (A pairs with T and C pairs with G).

Replication proceeds in both directions from the replication fork until the entire DNA molecule has been copied. The resulting two identical DNA molecules are each composed of one original strand and one new strand.

During DNA replication, errors can occur, such as the insertion or deletion of nucleotides or the pairing of the wrong nucleotides. To prevent these errors from being passed on to the next generation of cells, DNA polymerase has a proofreading function that can detect and correct many of these mistakes.

Overall, DNA replication is a critical process that ensures the accurate transmission of genetic information from one generation of cells to the next.

• • Gene Expression

Gene expression is the process by which information encoded in a gene is used to produce a functional product, such as a protein or RNA molecule. This process involves multiple steps, including transcription and translation.

Transcription is the first step in gene expression, during which the DNA sequence of a gene is used as a template to produce an RNA molecule. This is accomplished by the enzyme RNA polymerase, which binds to a specific region of the DNA called the promoter and then moves along the DNA strand, synthesizing a complementary RNA strand.

Once the RNA molecule is produced, it undergoes a series of modifications, such as splicing and capping, to form a mature RNA molecule that is ready to be translated into a protein.

Translation is the process by which the information contained in the RNA molecule is used to synthesize a protein. This process occurs on ribosomes, which are complexes made up of RNA and protein molecules. The ribosome reads the RNA sequence in groups of three nucleotides, called codons, and matches each codon to a specific amino acid.

As the ribosome moves along the RNA molecule, it adds each new amino acid to the growing protein chain, until the entire protein is produced.

The process of gene expression is regulated by a variety of factors, including environmental signals and internal cellular processes. These factors can control the rate of transcription or translation, or modify the RNA or protein molecules themselves.

Understanding gene expression is important for understanding the molecular basis of many biological processes, including development, disease, and evolution.

1. Mendel’s Laws of Inheritance
   • The Principle of Segregation

The principle of segregation, also known as Mendel’s first law, is a fundamental principle in genetics that explains how traits are inherited from one generation to the next. This principle states that during the formation of gametes (sex cells), the two alleles (versions of a gene) for each trait separate from each other, so that each gamete only receives one allele.

This means that when two individuals with different alleles for a given trait reproduce, each of their offspring will receive one allele from each parent, and the two alleles will segregate during gamete formation. As a result, the offspring can inherit either one of the two alleles for the trait from each parent, and the probability of inheriting a particular allele is 50%.

The principle of segregation is based on the fact that each individual has two copies of each gene, one inherited from each parent. These two copies may be identical (homozygous) or different (heterozygous) for a given trait. When two heterozygous individuals reproduce, there is a 25% chance that their offspring will inherit two copies of the same allele (homozygous dominant or homozygous recessive), a 50% chance that they will inherit one dominant and one recessive allele (heterozygous), and a 25% chance that they will inherit two copies of the recessive allele (homozygous recessive).

Overall, the principle of segregation explains how genetic variation is maintained within a population and how traits are passed from one generation to the next.

• • The Principle of Independent Assortment

The principle of independent assortment, also known as Mendel’s second law, is a fundamental principle in genetics that explains how traits are inherited independently of each other. This principle states that during gamete formation, the segregation of one gene pair (alleles of a single gene) is independent of the segregation of other gene pairs.

This means that the inheritance of one trait does not influence the inheritance of another trait. For example, if an individual has alleles for both brown hair and brown eyes, the alleles for these traits will be randomly sorted and distributed into different gametes during meiosis.

The principle of independent assortment is based on the fact that genes are located on different chromosomes, and their behavior during meiosis is independent of each other. This principle was first discovered by Gregor Mendel through his experiments with pea plants, in which he observed that the inheritance of seed color was independent of the inheritance of seed shape.

The principle of independent assortment has important implications for genetic variation and inheritance. It means that offspring can inherit different combinations of alleles from their parents, leading to a wide range of genetic variation within a population. This variation can then be subject to natural selection and other evolutionary processes, leading to changes in the frequency of different alleles over time.

Overall, the principle of independent assortment is an important concept in genetics that helps to explain how traits are inherited and how genetic variation is maintained within a population.

1. Dominant and Recessive Traits
   • Definitions of Dominant and Recessive Traits

Dominant and recessive traits are terms used to describe how different versions of a gene (alleles) are expressed in an organism’s phenotype (observable traits).

A dominant trait is a trait that is expressed when an individual has one or two copies of the dominant allele. In other words, the dominant allele masks the expression of the recessive allele. For example, if an individual has one dominant allele for brown eyes and one recessive allele for blue eyes, they will have brown eyes because the dominant allele is expressed.

A recessive trait is a trait that is only expressed when an individual has two copies of the recessive allele. If an individual has one dominant allele and one recessive allele for a trait, the dominant allele will be expressed and the recessive allele will be hidden. However, if two individuals with one recessive allele each for a trait reproduce, their offspring will inherit two recessive alleles and therefore express the recessive trait. For example, if both parents have one recessive allele for blue eyes, their offspring will have blue eyes.

It is important to note that dominance and recessiveness are not inherent properties of genes or alleles, but rather describe how the alleles interact with each other in a particular genetic context. Some traits may be incompletely dominant, meaning that the heterozygous individual expresses a phenotype that is intermediate between the dominant and recessive phenotypes. Additionally, some traits may be influenced by multiple genes and environmental factors, making the inheritance patterns more complex.

• • Punnett Squares: Predicting Offspring Traits

Punnett squares are a tool used in genetics to predict the possible genotypes and phenotypes of offspring resulting from a cross between two individuals.

To construct a Punnett square, the alleles of each parent are written along the top and left sides of a grid. The possible gametes (sperm or egg cells) for each parent are then combined to create all possible combinations of alleles in the offspring. The resulting genotypes and phenotypes of the offspring are then determined based on the rules of Mendelian inheritance.

For example, consider a cross between two heterozygous individuals (Aa) for a trait controlled by a single gene with two alleles (A and a). The Punnett square for this cross would be a 2×2 grid, with the alleles A and a written along the top and left sides. The four boxes in the grid represent the possible genotypes of the offspring, which are AA, Aa, aA, and aa.

To determine the probabilities of each genotype, the alleles in each box are combined. For example, the box in the top left corner contains an A from the father and an A from the mother, resulting in an offspring with the genotype AA. The same process is repeated for the other boxes in the grid.

To determine the probabilities of each phenotype, the genotypes are translated into their corresponding traits. In this example, the dominant allele A produces a certain trait, while the recessive allele a produces a different trait. Therefore, the offspring with the genotypes AA and Aa will have the dominant trait, while the offspring with the genotype aa will have the recessive trait.

Overall, Punnett squares are a useful tool for predicting the possible outcomes of a genetic cross and understanding the principles of Mendelian inheritance.

1. Pedigree Analysis: Tracing Inheritance Patterns
   • Understanding Pedigree Charts

Punnett squares are a tool used in genetics to predict the possible genotypes and phenotypes of offspring resulting from a cross between two individuals.

To construct a Punnett square, the alleles of each parent are written along the top and left sides of a grid. The possible gametes (sperm or egg cells) for each parent are then combined to create all possible combinations of alleles in the offspring. The resulting genotypes and phenotypes of the offspring are then determined based on the rules of Mendelian inheritance.

For example, consider a cross between two heterozygous individuals (Aa) for a trait controlled by a single gene with two alleles (A and a). The Punnett square for this cross would be a 2×2 grid, with the alleles A and a written along the top and left sides. The four boxes in the grid represent the possible genotypes of the offspring, which are AA, Aa, aA, and aa.

To determine the probabilities of each genotype, the alleles in each box are combined. For example, the box in the top left corner contains an A from the father and an A from the mother, resulting in an offspring with the genotype AA. The same process is repeated for the other boxes in the grid.

To determine the probabilities of each phenotype, the genotypes are translated into their corresponding traits. In this example, the dominant allele A produces a certain trait, while the recessive allele a produces a different trait. Therefore, the offspring with the genotypes AA and Aa will have the dominant trait, while the offspring with the genotype aa will have the recessive trait.

Overall, Punnett squares are a useful tool for predicting the possible outcomes of a genetic cross and understanding the principles of Mendelian inheritance.

• • Tracing Inherited Traits through Pedigrees

Pedigrees are charts that show the inheritance of traits through a family or population. They are useful tools for tracing the transmission of genetic traits over several generations and can help geneticists determine the mode of inheritance of a particular trait.

In a pedigree, circles represent females and squares represent males. A horizontal line connects two individuals who have had children together, and vertical lines connect their offspring to them. Each individual is labeled with their genotype or phenotype for the trait being studied.

By analyzing the pattern of inheritance in a pedigree, geneticists can determine whether a trait is inherited in a dominant or recessive manner. In a dominant pedigree, at least one parent with the dominant trait will have offspring with the same trait. In a recessive pedigree, two carriers of the recessive trait must have offspring with the trait for it to be expressed.

Pedigrees can also be used to track the inheritance of X-linked or mitochondrial traits, which are inherited differently than traits controlled by autosomal genes. X-linked traits are carried on the X chromosome and are more common in males, while mitochondrial traits are inherited from the mother and can affect both males and females.

Overall, pedigrees are important tools for understanding the inheritance of genetic traits and can help geneticists identify individuals who may be at risk for certain genetic diseases.

1. Genetic Disorders: An Overview
   • Common Genetic Disorders

Genetic disorders are conditions caused by changes or mutations in genes. Some genetic disorders are inherited from one or both parents, while others occur spontaneously due to new mutations. Here are some examples of common genetic disorders:

1. Down Syndrome – a chromosomal disorder caused by the presence of an extra copy of chromosome 21, resulting in developmental delays, intellectual disability, and characteristic facial features.
2. Cystic Fibrosis – an autosomal recessive disorder caused by mutations in the CFTR gene, resulting in abnormal production of mucus in the lungs, pancreas, and other organs.
3. Sickle Cell Anemia – an autosomal recessive disorder caused by mutations in the HBB gene, resulting in abnormal hemoglobin production and the characteristic sickle-shaped red blood cells, which can cause pain, organ damage, and increased susceptibility to infections.
4. Huntington’s Disease – an autosomal dominant disorder caused by mutations in the HTT gene, resulting in progressive degeneration of the brain and loss of motor and cognitive function.
5. Hemophilia – an X-linked recessive disorder caused by mutations in the F8 or F9 gene, resulting in impaired blood clotting and increased risk of bleeding.
6. Fragile X Syndrome – a disorder caused by mutations in the FMR1 gene, resulting in intellectual disability, developmental delays, and characteristic physical features.
7. Tay-Sachs Disease – an autosomal recessive disorder caused by mutations in the HEXA gene, resulting in progressive neurological deterioration and death in early childhood.

These are just a few examples of the many genetic disorders that exist. Genetic counseling and testing can help individuals and families determine their risk for these and other genetic conditions.

• • Causes and Symptoms of Genetic Disorders

Genetic disorders can be caused by mutations or changes in one or more genes. These mutations can occur spontaneously during DNA replication or may be inherited from one or both parents. Here are some common causes of genetic disorders:

1. Chromosomal abnormalities – such as Down syndrome, which occurs when there is an extra copy of chromosome 21.
2. Single gene mutations – such as cystic fibrosis, sickle cell anemia, and Huntington’s disease, which are caused by mutations in a single gene.
3. Multifactorial inheritance – such as heart disease, diabetes, and some cancers, which are caused by a combination of genetic and environmental factors.

The symptoms of genetic disorders can vary widely depending on the specific condition. Some genetic disorders may be mild, while others can be severe and life-threatening. Symptoms may include:

1. Developmental delays or intellectual disability
2. Abnormal physical features or growth patterns
3. Increased susceptibility to infections or diseases
4. Vision or hearing loss
5. Chronic pain or disability
6. Behavioral or emotional problems
7. Increased risk of certain types of cancer

It’s important to note that not all genetic mutations result in disorders, and many individuals may be carriers of genetic mutations without ever displaying symptoms themselves. Genetic counseling and testing can help individuals and families determine their risk for genetic disorders and make informed decisions about their healthcare.

1. Applications of Genetic Engineering
   • Genetic Modification in Plants and Animals

Genetic modification in plants and animals involves the manipulation of an organism’s DNA to introduce new traits or characteristics. This can be done through a variety of techniques, including gene editing, gene insertion, and gene deletion.

In plants, genetic modification is commonly used to create crops that are resistant to pests and diseases, have improved nutritional content, or can tolerate environmental stressors such as drought or extreme temperatures. For example, scientists have developed genetically modified soybeans that are resistant to herbicides, corn that produces its own insecticide, and rice that contains additional nutrients such as vitamin A.

In animals, genetic modification is used to create animal models for research, to develop new treatments for human diseases, or to create animals with specific traits or characteristics. For example, scientists have created genetically modified mice that are susceptible to certain types of cancer, goats that produce human proteins in their milk for use in pharmaceuticals, and pigs with organs that are compatible with human transplant recipients.

While genetic modification has the potential to provide many benefits, it is also a controversial topic due to concerns about the safety and ethical implications of manipulating an organism’s DNA. Some worry that genetically modified organisms could have unintended consequences for the environment or human health, while others argue that genetic modification could be used to address pressing issues such as food insecurity and climate change.

Regulation of genetic modification varies by country, and many countries have strict regulations in place to ensure the safety of genetically modified organisms before they can be used commercially or released into the environment.

• • The Role of CRISPR-Cas9

CRISPR-Cas9 is a powerful gene-editing tool that has revolutionized the field of genetic engineering. It is a system that allows researchers to make precise changes to an organism’s DNA, enabling them to add, delete, or replace specific genes or sequences.

The CRISPR-Cas9 system is based on a naturally occurring defense mechanism found in bacteria, which uses RNA molecules to target and destroy invading viruses. Researchers have harnessed this mechanism to create a gene-editing tool that can be used to modify DNA sequences in a variety of organisms.

The process involves designing a small RNA molecule that can target a specific sequence of DNA. The RNA molecule is then combined with an enzyme called Cas9, which acts like a pair of molecular scissors to cut the DNA at the targeted location. This allows researchers to insert new genes, delete unwanted genes, or repair genetic mutations.

The potential applications of CRISPR-Cas9 are vast, ranging from creating new disease treatments to developing more resilient crops. For example, scientists are using CRISPR-Cas9 to develop new cancer therapies that target specific genetic mutations, and to create crops that are more resistant to pests and environmental stressors.

Despite its potential, there are also concerns about the ethical implications of using CRISPR-Cas9 to manipulate the genetic makeup of organisms. Critics argue that the technology could be used to create “designer babies” with specific traits, or to create organisms with unintended and potentially harmful consequences. As with all emerging technologies, it is important to carefully consider the potential benefits and risks before using CRISPR-Cas9.

1. Frequently Asked Questions about HEREDITY
   • What is HEREDITY?

Heredity refers to the passing on of traits or characteristics from parents to their offspring through the transmission of genetic information. This genetic information is carried by DNA, which contains the instructions for the development and function of all living organisms

• • How are traits inherited?

Traits are inherited through the transmission of genetic material from parents to offspring. This genetic material is carried in the form of DNA (deoxyribonucleic acid), which contains the instructions for the development and function of all living organisms.

• • What is a gene?

A gene is a unit of heredity that is passed on from parents to their offspring and carries the instructions for the development, function, and traits of living organisms. Genes are segments of DNA (deoxyribonucleic acid) located on chromosomes, which are structures within the cell nucleus that contain genetic material.

• • What is DNA?

DNA (Deoxyribonucleic acid) is a molecule that carries genetic information and instructions for the development, function, growth, and reproduction of all living organisms. It is a long, double-stranded helical structure composed of nucleotides, which are the building blocks of DNA.

The four nucleotides that make up DNA are adenine (A), thymine (T), cytosine (C), and guanine (G). These nucleotides pair up in a specific way – A always pairs with T, and C always pairs with G – to form the base pairs that make up the rungs of the DNA ladder.

• • What is genetic engineering?

Genetic engineering is the process of manipulating an organism’s DNA (deoxyribonucleic acid) in order to modify its genetic makeup, traits or characteristics. This involves inserting, deleting, or altering genes within an organism’s genome, which can result in changes in its physical and functional properties.

1. Conclusion

• • Heredity plays a significant role in the development, function, and characteristics of all living organisms. It is the process by which genetic material is passed down from one generation to the next, ensuring the continuation of life and the perpetuation of traits and characteristics that are essential for survival.

genetic research has the potential to bring about significant advances in medicine, agriculture, and biotechnology. However, it is important to carefully consider the ethical and social implications of these advances and ensure that they are used in a responsible and beneficial way.

Bullet Points:

• Genes are the basic units of heredity that determine the traits we inherit from our parents.
• Traits can be either physical or physiological characteristics.
• Chromosomes are made up of DNA and contain genes.
• DNA carries genetic information and is responsible for passing down traits from one generation to the next.
• Mendel’s laws of inheritance describe how traits are passed down from parents to offspring.
• Dominant traits are always expressed, while recessive traits are only expressed when paired with another recessive trait.
• Pedigree analysis is a tool used to trace inheritance patterns through generations.
• Genetic disorders are caused by mutations in genes and can have significant impacts on an individual’s health.
• Genetic engineering allows scientists to modify DNA and create new traits in plants and animals.

FAQs:

Q: What is HEREDITY? A: HEREDITY is the passing down of traits from parents to their offspring.

Question: 1 What is heredity? 

Answer: transfer of characteristics from generation to generation.

Question: 2 Inheritance from the previous generation provides what?

Answer: inheritance from the previous generation provides both a common basic body design and subtle changes in it.

Question: 3 What happens when the second generation reproduces?

Answer: the second generation will have differences that they inherit from the first generation as well as newly created differences.

Question: 4 What is a gene?

Answer: Factors which are responsible for expressing characteristics.

Question: 5 What do you mean by inherited traits?

Answer: the traits which we get it from our parents

Question: 6 Why does the human population show a great deal of variation ?

Answer because human use sexual mode of reproduction.

Question: 7 What is variation? 

Answer:The differences in the characters between the parent and offspring.

Question: 8 What is the importance of variations?

Answer: (1) Depending upon the nature of variation different individuals have different advantages. 

(2) Main advantage of variation of species is that it increases the chances of its survival in a changing environment. 

Question: 9 What are the causes of variations? 

Answer:1) Recombination or crossing over is one of the important reasons for variations. 

2) It is an exchange of chromosome segments at the time of gamete formation. 

Question: 10 What are dominant and recessive traits?

Answer: Dominant trait is a gene which expresses its character and recessive is a trait who does not express its character.

Question: 11 Who is known as the father of genetics? 

Answer: Georg John Mendel. 

Question:12 In which year Mandal was born?

Answer 1822

Question: 13 Which characters of pea plants were stuied by Mendel ?

Answer:Mandal used a number of contrasting visible characters. For example round/wrinkled seeds,tall/short,white/purple.

Question :14 From where Mendel get educated ?

Answer : Mendel was educated in a monastery.

Question :15 From where he studies science and maths ?

Answer : Mendel studies science and maths from the University of Vienna. 

Question :16 Where  did he grow pea plant 

Answer : He grows pea plants at a monastery.

Question :17 How did Mendel calculate the number of plants obtained in the progeny generation?

Answer :In percentages of characteristics of plants.

Question:18 Were the tall plants in the F1 generation exactly the same as the tall plant of the parent generation?

Question:19 What happens to pea plants showing two different characteristics?

Answer: It is not possible.

Question:20 What do the progeny of a tall plant with round seeds and a short plant with wirnkled seeds look like?

Question: 21 Why did Mendel choose a pea plant for the experiment? 

Answer: 1) Availability of detectable contrasting traits of several characters. 

2) Short life span of the plant. 

3) Normally allows self pollination but cross pollination can be carried out. 

Question:22 What is the phenotype ratio of pea plants in the second generation?

Answer:-  3 : 1

Question: 23 What is the genotype ratio of the plants in the second generation?

 Answer:- 1 : 2 : 1

Question: 24 What is the phenotype?

Answer Phenotype refers to the change in individuals which can easily see and observe.

Question: 25 What is the genotype?

Answer: the changes in the genes which we can not see but we can observe, is called its genotype.

Question: 26 How do genes control characteristics?

Answer : Genes control characteristics by dominant and recessive nature of them.

Question. 27 How does the mechanism of heredity work ?

Answer: The mechanism of heredity works with the help of genes which are responsible for transferring genitical character.

Question:28 Which hormone is responsible for growth in plants ?

Answer Auxin hormone.

Question: 29 Write the names of laws of Mendel?

Answer ; law of dominant ‘ law of segregation law of independent assortment

Question:30 Explain the law of dominance ?

Answer : Some alleles are dominant and cover up recessive alleles .

Question:31 Explain the law of segregation ?

Answer : An organism has 2 alleles for each gene but they can only pass on one.

Question:32 Explain the law of independent assortment?

Answer : Genes found on separate chromosomes are inherited independently of each other.

Question:33 How are new combinations of traits formed in F2 offspring?

Answer:- When factor controlling for seed shape and seed colour recombine to form zygote leading to form F2 offspring.

Question:34 What happens if the interpretation of the Mendelian experiment was correct?

Answer:-Then both parents must be contributing equally to the DNA of the progeny during sexual reproduction.

Question:35 In what case the plant will be tall?

Answer:- if the enzymes work efficiently alot of hormones will be made and the plant will be tall.

Question:36 in what case  the plant will be short?

Answer:- if the gene for that enzyme has an alteration that makes the enzyme less efficient the amount of our moon will be less and the plant will be short. 

Question:37 How do germ cells make a single set of genes from the normal two copies?

Answer:-  Due to meiosis germ cells make a single set of genes from the normal two copies.

Question:38 What happens when two germ cells combine?

Answer:- When two germ cells combine,they will restore the normal number of chromosomes in progeny, ensuring the stability of the DNA of species.

Question:39 What is sex determination? 

Answer:- Sex determination is used to define the sex of offspring and genetic factors detrimine the sex of the offspring. 

Question:40 In human sex or gender is determined by whom? 

Answer:- By sex chromosomes. 

Question:41 What are sex chromosomes? 

Answer:- In human beings, there are 23 pairs of chromosomes, and last decides pair decides the gender called sex or gender chromosomes. cromosomes that are responsible for determines sex in indiviadual called sex cromosomes.

Question:42 What are the observations after  crossing between a tall and a short plant? 

Answer:- 1) All F1 progeny were tall, no medium height plant. 

2) F2 ¼ were short and the rest were tall. 

3) Phenotypic ratio F2=3:1

4)Genotypic ratio F2=1:2:1.

Question:43 What are the observations after crossing between round and wrinkled plants? 

Answer:- 1) When RRYY were crossed with rryy in F1 progeny all were RrYy round and yellow seeds. 

2) Self pollination of F1 plants gave parental phenotype and two  seeds plants in the ratio of 9:3:3:1.

Question:44 Which sex cromosomes found in humans?

Answer:- Women have a pair of XX chromosomes while men have a mismatched pair in which one is Y and other is X.

Question: 45 By whom the sex of the children will be determined ?

Answer:- The sex of the children will be determined by inherit of their father, Because only father have both X and Y chromosomes.

Question:46 How sex determined in human?

Answer:- Half of the male gametes carry X chromosome and half of Y. All the female gametes carry X chromosomes. When a sperm fertilises an egg, the following situations become possible.:

1. When a sperm carrying X chromosome fertilises an egg that contains only X chromosome, the resulting zygote develops into a female XX condition. 
2. When a sperm carrying Y chromosome fertilises an egg that contains only X chromosomes the resulting zygote develops into a male XY. 
3. Thus, there are 50-50 chances of a male or a female child. 

Question:47 Human beings have how many pairs of chromosome

Answer: Most human chromosomes have maternal paternal copy and we have such pairs but one pair called the sex chromosome odd in not always a being a perfect pair.