Dihybrid Cross: Mendel’s Experiment, Traits & Alleles

Ans: A dihybrid cross is a cross in which two traits are taken into account during the testing process. A dihybrid cross is a cross between a yellow smooth seeded pea plant and a green wrinkled seeded pea plant.
The Law of Independent Assortment can be deduced from the dihybrid cross that each gene is assorted independently of the other throughout its passage from one generation to the next.

Ans: Advantages of selecting pea plant as experimental material: Mendel selected the pea plant (Pisum sativum) because:

1. There were numerous varieties with observable alternate versions for a trait or characteristic.
2. Peas self-pollinate because their corolla completely encloses the reproductive organs until pollination is complete.
3. It was simple to obtain.
4. It has pure lines for testing purposes, which means that they always breed true.
5. It has contrasting personalities. Seed color, pod color, pod shape, flower shape, flower location, seed shape, and plant height were the traits studied.
6. It had a brief life cycle and a big number of offspring.
7. Except for pollination, the plant is simple to cultivate and requires no special attention.

Ans: Law of independent assortment: The components of distinct pairs of opposing characters, according to this law, have no influence on one another. During gamete formation, they are independent of one another in their arrangement to form a new combination. Cross between two hybrids. A dihybrid cross is a cross in which two traits are taken into account during the testing process.

It's thought to be a cross between a yellow smooth pea plant and a green wrinkled pea plant.
Explanation: When a pea plant with yellow smooth seeds (YYSS) crosses with a pea plant with green wrinkled seeds, the result is a pea plant with green wrinkled seeds (yyss). Yellow smooth (YYSS) produces gametes with genes (YS) during cross-pollination, while green-wrinkled produces gametes with genes (YS) (ys). At random, gametes combine. Because yellow and smooth features predominate over green and wrinkled, the seeds collected will grow into plants and generate seeds that are yellow-smooth (YySs). Plants of the F1 When plants of the F1 generation are allowed to self-pollinate gametes formed YS, Ys, yS, and ys by meiosis, they unite at random forming seeds. The plants thus obtained are called F2 generation plants. They are yellow-smooth (YYSS, YySS, YySs, YYSs); yellow-wrinkled (YYss, Yyss), green smooth (yySS, yySs), and green-wrinkled (yyss) in the ratio of 9: 3: 3: 1. The result of a dihybrid cross can be shown in Fig. on the chequerboard.

It can be concluded from the preceding dihybrid cross that each gene is assorted separately of the others during its passage from generation to generation, or that the law of independent assortment is justified.

Ans: A test cross is a genetic cross between a homozygous recessive individual and a suspected heterozygote to determine the latter's genotype.
The origin experiment Mendel conducted himself to determine the genotype of a yellow pea is a classic example of the test cross. The alleles Y and y are utilized for the yellow and green variants of the allele, respectively, as shown in the image below. The Y allele, which is yellow, is dominant over the y allele. As a result, only the yellow allele is seen in the phenotypic of an organism with the genotype Yy. Mendel had a yellow pea and was trying to figure out if it was YY or Yy.

Ans: 

1. Establishing a parental cross would be the first step (P).
2. Then, for the traits to be crossed, build a 4x4 (or 16 square) Punnett Square.
3. Determine the genotypes of the parents and assign letters to the alleles, using lowercase letters for recessive traits and uppercase letters for dominant traits.
4. Arrange the qualities on the square — recessive traits only occur if both parents have recessive traits, according to logic. For instance, if both parents carry the recessive trait "f," the emerging trait will be ("ff"). If one of the parents possesses the letter "F," the ensuing feature will be "Ff," not "fF."

Ans: Morgan noticed that the two genes did not segregate independently and that the F2 ratio was significantly different from the 9:3:3:1 ratio.
He attributed this to the physical relationship or linkage of two genes, coining the terms linkage and recombination to describe non-parental gene pairings.
Morgan and his colleagues discovered that even when genes were grouped on the same chromosome, some were firmly coupled (with little recombination) and others were loosely linked (showing higher recombination). The phenotypes round, yellow; wrinkled, yellow; round, green; and wrinkled, green occurred in the Mendelian dihybrid cross in the ratio 9:3:3:1.

Wrinkled, yellow, round, green is possible because the distance between the two genes is greater. Therefore, recombination of the parental type is possible.

Ans: A single gene determines the shape of the seed. The (R) is for the round shape, which is dominant over (r) for the wrinkled seed. If homozygous alleles control the seed shape, it will depict the phenotype of the same alleles, for eg., RR (round), rr (wrinkled). If the alleles are heterozygous, the phenotype of the dominant allele will be expressed, for eg., Rr (round).

Ans: The standard dihybrid ratio observed is 9:3:3:1. If the two genes interact ‌the values will deviate. This is because when ‌genes are linked, they do not exhibit independent assortment and remain together in the gametes and the offspring. The dihybrid ratio thus obtained is 3:1.

Ans: Autosome- All chromosomes apart from the sex chromosomes are called the Autosomes. The number of autosomes differs from one organism to another. Humans have 44 numbers or 22 pairs of autosomes.

Hemizygous- It is a condition in which an organism has only one copy of a gene or DNA sequence present in diploid cells.

Homozygous- It is a condition in which an organism has two similar alleles of a given gene (XX).

Heterozygous- It is a condition in which an organism has two different alleles of a given gene (XY).

Ans:

1. It is a dihybrid test cross.

3. It illustrates the principle of independent assortment.

Ans:

Ration: Barking & erect = 9

Barking & drooping = 3

Silent & erect = 3

Silent & Drooping = 1

Phenotypic ratio = 9:3:3:1