NCERT Solution for Class 10 Science Chapter 9
Heredity and Evolution
NCERT Books for Session 2022-2023
CBSE Board and UP Board
Exercises Questions
Page No-159
Questions No-11
How is the equal genetic contribution of male and female parents ensured in the progeny?
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In human beings, every somatic cell of the body contains 23 pairs of chromosomes. Out
of these 23 pairs, the first 22 pairs are known as autosomes and the remaining one pair
is known as sex chromosomes represented as X and Y.
Females have two X chromosomes and males have one X and one Y chromosome. The
gamete receives half of the chromosomes. Therefore, the male gametes have 22
autosomes and either X or Y chromosome.
The female gamete, on the other hand, has 22 autosomes and X chromosome.
During reproduction, the male and female gametes fuse and thus the progeny receives 22
autosomes and one X or Y chromosome from male parent and 22 autosomes and one X
chromosome from the female parent.
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In human beings, equal genetic contribution of male and female parents is ensured in the progeny through inheritance of equal number of chromosomes from both parents. There are 23 pairs of chromosomes All human chromosomes are not paired. Out of these 23 pairs, the first 22 pairs are known as autosomes and the remaining one pair is known as sex chromosomes represented as X and Y. Females have a perfect pair of two X sex chromosomes and males have a mismatched pair of one X and one Y sex chromosome.
During the course of reproduction, as fertilization process takes place, the male gamete (haploid) fuses with the female gamete(haploid) resulting in formation of the diploid zygote. The zygote in the progeny receive an equal contribution of genetic material from the parents. Out of 23 pairs of chromosomes in progeny, male parent contributes 22 autosomes and one X or Y chromosome and female parent contributes 22 autosomes and one X chromosome.
Gametogenesis involves meiosis which leads to haploidy in the gametes. A zygote thus gets 50% of genes from each parent. Thus, equal genetic contribution is ensured from male and female parents.
The equal genetic contribution of male and female parents to their progeny is ensured through a biological process known as sexual reproduction. In sexual reproduction, genetic material from both parents is combined to produce offspring with a mix of characteristics from each parent. Here’s how this equal genetic contribution is achieved:
Gamete Formation: Both males and females produce specialized reproductive cells called gametes. In males, these are sperm cells, and in females, these are egg cells (ova). Gametes are haploid, meaning they contain half the number of chromosomes (genetic material) as the normal body cells, which are diploid.
Meiosis: The formation of gametes involves a specific type of cell division called meiosis. During meiosis, the number of chromosomes in the parent cell is halved, resulting in four unique haploid gametes. In humans, this reduces the chromosome number from 46 (diploid) to 23 (haploid).
Fertilization: When a sperm cell from the male fertilizes an egg cell from the female, their haploid nuclei combine, creating a diploid zygote. This process restores the diploid chromosome number necessary for the normal development of an organism. Fertilization results in the equal genetic contribution of both parents to the offspring.
Genetic Variation: While both parents contribute equally to the genetic material of their offspring, genetic variation occurs due to the random assortment of alleles and the crossing over of genetic material during meiosis. This variation ensures that each offspring is unique and not an exact copy of either parent.
In summary, the equal genetic contribution of male and female parents is ensured through the formation of haploid gametes and their subsequent fusion during fertilization, resulting in a diploid zygote with genetic material from both parents. This process is fundamental to sexual reproduction and contributes to the genetic diversity of populations.