Quick Revision Notes & Formula Sheet

Class: 10th Science
Chapter: Heredity
Board: MP Board (NCERT Curriculum)

---

1. Important Definitions (महत्वपूर्ण परिभाषाएँ)

• Heredity (आनुवंशिकता): The transmission of characters (traits) from parents to their offspring (progeny).
• Variation (विविधता): The differences in characters shown by individuals of the same species and by the offspring of the same parents.
• Genotype (जीनोटाइप): The genetic constitution (makeup) of an organism. It represents the alleles present in an organism (e.g., TT, Tt, tt).
• Phenotype (फीनोटाइप): The observable physical or biochemical characteristics of an organism, determined by both genetic makeup and environmental factors (e.g., Tall or Dwarf).
• Alleles (युग्मविकल्पी): Alternative forms of a gene that occupy the same position on a chromosome and determine distinct traits.
• Dominant Trait (प्रभावी लक्षण): A trait that expresses itself in both homozygous and heterozygous conditions (represented by a capital letter, e.g., 'T').
• Recessive Trait (अप्रभावी लक्षण): A trait that expresses itself only in the homozygous condition (represented by a small letter, e.g., 't').
• Homozygous (समयुग्मजी): Having identical alleles for a particular trait (e.g., TT or tt).
• Heterozygous (विषमयुग्मजी): Having different alleles for a particular trait (e.g., Tt).
• Speciation (जाति उद्भव): The formation of new and distinct species in the course of evolution due to genetic drift, natural selection, or geographical isolation.
• Homologous Organs (समजात अंग): Organs which have the same basic structural design and origin but may perform different functions in various species (e.g., Forelimbs of humans and wings of birds). Indicates common ancestry.
• Analogous Organs (समवृत्ति अंग): Organs which have different basic structure and origin but perform similar functions (e.g., Wings of bats and birds). Indicates convergent evolution.
• Fossils (जीवाश्म): The preserved remains or traces of animals, plants, and other organisms from the remote past.

---

2. Mendel's Laws of Inheritance (मेंडल के आनुवंशिकता के नियम)

Gregor Johann Mendel is known as the Father of Genetics. He used garden peas (Pisum sativum) for his hybridization experiments.

A. Law of Segregation (पृथक्करण का नियम)

• Statement: The alleles of a gene separate during gamete formation so that each gamete carries only one allele for each gene.
• Key Point: Alleles do not show any blending; traits are recovered in the $F_2$ generation though one of these is not seen in the $F_1$ generation.

B. Law of Independent Assortment (स्वतंत्र अपव्यूहन का नियम)

• Statement: When two pairs of traits are combined in a hybrid, segregation of one pair of characters is independent of the other pair of characters.
• Exemplified by: Dihybrid cross.

---

3. Crosses and Ratios (संकरण और अनुपात)

A. Monohybrid Cross (एकसंकर संकरण)

• Cross between two parents differing in a single pair of contrasting characters (e.g., Height: Tall TT $\times$ Dwarf tt).
• $F_1$ Generation: All plants are tall (Tt).
• $F_2$ Generation Ratios (from selfing Tt $\times$ Tt):
  • Phenotypic Ratio: $3 : 1$ (3 Tall : 1 Dwarf)
  • Genotypic Ratio: $1 : 2 : 1$ (1 Pure Tall TT : 2 Hybrid Tall Tt : 1 Pure Dwarf tt)

B. Dihybrid Cross (द्विसंकर संकरण)

• Cross between two parents differing in two pairs of contrasting characters (e.g., Seed shape and seed color: Round/Yellow RRYY $\times$ Wrinkled/Green rryy).
• $F_1$ Generation: All seeds are Round and Yellow (RrYy).
• $F_2$ Generation Phenotypic Ratio: $9 : 3 : 3 : 1$
  • 9 (Round, Yellow) : 3 (Round, Green) : 3 (Wrinkled, Yellow) : 1 (Wrinkled, Green)

---

4. Sex Determination in Humans (मनुष्यों में लिंग निर्धारण)

• Human beings have 23 pairs of chromosomes (46 total chromosomes).
• Autosomes (कायिक गुणसूत्र): 22 pairs (same in males and females).
• Sex Chromosomes (लिंग गुणसूत्र): 1 pair.
  • Females have a perfect pair: XX
  • Males have a mismatched pair: XY

Probability of Child's Gender:

• Mother produces eggs with X chromosome only.
• Father produces two types of sperms: 50% carrying X chromosome and 50% carrying Y chromosome.
• Conclusion: The sex of a child is determined by what they inherit from the father (whether the sperm carries X or Y).

---

5. Important Points for Objective Questions (बहुविकल्पीय प्रश्नों के लिए मुख्य बिंदु)

1. Father of Genetics: Gregor Johann Mendel.
2. Plant used by Mendel: Garden Pea (Pisum sativum).
3. Why pea plant? Easy to grow, distinct contrasting characters, self-pollinating and cross-pollinating easily, short life cycle.
4. DNA: Deoxyribonucleic Acid – the carrier of hereditary information in most organisms.
5. Gene: Functional unit of heredity made up of DNA.
6. Fossils age estimation: Carbon dating method.