Class 10 Chapter 8 Heredity 

• Reproduction produces offspring that are similar yet subtly different.
• प्रजनन प्रक्रिया नए जीवों को जन्म देती है जो अपने माता-पिता के समान होते हैं, लेकिन उनमें कुछ अंतर भी होते हैं।
• Heredity is the transmission of characters from parents to offspring.

• Variations arise due to small DNA copying inaccuracies.
• Asexual Reproduction: Very low variation (e.g. Sugarcane field). Only minor differences.
• Sexual Reproduction: High variation due to recombination. Diversity is maximized.

• Survival Advantage: Variations help species survive environmental changes.
• Best Example: Bacteria that can withstand heat will survive a heatwave better than others. (गर्मी सहन करने वाले बैक्टीरिया लू में जीवित रहेंगे।)
• Selection of variants by environmental factors forms the basis of Evolutionary Processes.

• Gregor Johann Mendel (1822-1884): Father of Genetics.
• He used Garden Pea (Pisum sativum) for his experiments.
• मेंडल ने मटर के पौधों के विपरीत लक्षणों (Contrasting Traits) का अध्ययन किया।

Crossing plants with one pair of contrasting characters (e.g. Height).

• Dominant Trait (प्रभावी लक्षण): The trait that appears in F1 (e.g. Tallness ‘T’).
• Recessive Trait (अप्रभावी लक्षण): The trait that remains hidden in F1 but reappears in F2 (e.g. Shortness ‘t’).
• Phenotypic Ratio (F2) = 3 : 1
  Genotypic Ratio (F2) = 1 : 2 : 1 (TT : Tt : tt)

Study of inheritance of two pairs of traits simultaneously.

उदाहरण: बीज का आकार (Round/Wrinkled) और रंग (Yellow/Green)।

• Traits are inherited independently of each other.
• लक्षण एक-दूसरे से स्वतंत्र रूप से अगली पीढ़ी में जाते हैं।
• The inheritance of seed shape has nothing to do with seed color.

• Cellular DNA is the information source for making proteins.
• Gene: A section of DNA that provides info for one protein.

Example of Tallness:

• Plant Height depends on amount of Plant Hormone.
• Enzyme (Protein) controls the amount of hormone.
• Efficient enzyme $\implies$ More hormone $\implies$ Tall Plant.
• Altered gene $\implies$ Less efficient enzyme $\implies$ Less hormone $\implies$ Short Plant.

• Both parents contribute equally to the DNA of the progeny.
• Each germ cell (gamete) has only one set of genes.
• Genes are present on separate threads called Chromosomes.
• Normal human cells: 2 copies of each chromosome (Diploid).
• Germ cells: 1 copy of each chromosome (Haploid).

Stability of DNA is restored by fusion of 2 germ cells.

• Different species use different strategies.
• Environmental cues: In some reptiles (turtles/lizards), the temperature at which eggs are kept determines sex.
• Changing Sex: Snails can change sex, meaning it’s not always genetic.

Sex Determination in Humans:

• Humans have 23 pairs of chromosomes.
• 22 pairs are perfect pairs (Autosomes).
• 1 pair is Sex Chromosome.
• Females: XX (Perfect pair)
• Males: XY (Mismatched pair, Y is short)