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Mendel’s law of independent assortment demonstrates that two physical traits can express their individual traits independently may it be dominant or recessive, indicating that each allelic form is unpaired in gametes. This forms the basic principle of sex determination in human beings. Tutorspoint provides Mendels Law of Inheritance Homework Help
Mendel’s law of independent assortment
We have learned that physical traits are expressed due to segregation of different allelic forms of the genes. Further, we need to understand how two physical traits like round/wrinkled seeds are expressed along with green/yellow pods. Mendel’s law of independent assortment clarified the relation of different pairs of alleles. Mendel crossed plants with round, yellow seeds with plants with wrinkled, green seeds.
The homozygous parent plants cross resulted in heterozygous F1 plants. Since the F1 plants were heterozygous for two gene pairs, they were also called as dihybrids and the cross was termed as dihybrid cross. It was known that alleles for round, yellow seeds were dominant over their respective alleles. Hence F1 plants resulted in the round, yellow seeds.
On self-fertilizing the F1 hybrids, four F2 phenotypes were observed. Out of total 556 plants, 315 were found to be plants with round, yellow seeds; 108 were found to have round, green, 101 were wrinkled, yellow and 32 were wrinkled green. These statistics fitted a ratio of 9:3:3:1 (see Figure 1)
From these results, Mendel concluded that the chance of two or more independent events occurring together is the product of the chances of their separate occurrences. In short, the members of different pairs of alleles assort independently into gametes.
Sex determination in humans is decided by the sex chromosomes present in male and female gametes. The sex chromosomes X and Y are also known as allosomes.
Every female human has two copies of X chromosomes, while a male has one copy of X and one copy of Y chromosome present in their gametic cells. After copulation, the sperms cells of male containing two gametes - X and Y chromosome fuse with the X chromosome present in the egg of the female. Two possible combinations occur as a selective chance to form a zygote, indicating that zygote can be either XX or XY resulting in female or male offspring respectively.