Question

I have the answers to the two question below. Can you help explain why the answers please. Thanks

Considering factors that account for the differences in Gene/ Allelic expression that lead to modidied Mendelian ratios. Tell whether the statements are True and Flase. a. Modified Mendelian ratios do arise as a result of patial expression of alleles in the heterozygote. True b. Typical Mendelian ratios are the result of the simultaneous expression of two alleles in the heterozygote. False c. Pleiotrophy results in modified ratios in some cases. True

In the Rex, Rabbit, The Length of the fur can be short, medium or long and the color can be sable or black. Several rabbits with black , long fur were crossed to rabbits that had short, sable fur. all the f1 rabbits had black, medium length fur. When the f1 were inbred, the following f2 phenotypes were observed

3/16 Long, black 1/16 Long, sable 6/16 medium, black 2/16 medium, sable 3/16 short, black 1/16 short, sable

A. How many genes control phonotypes observed in the above date? 1

B. What is the genotype of the medium fur length rabbits with sable colored fur. Aabb

  

Answer 1

1. True

The statement is correct with respect to incomplete dominance. In this type of inheritance, the dominant allele is partially dominant over the recessive allele. Therefore it is not able to express itself completely. Hence we see an intermediate phenotype in the heterozygotes which is in between the two extreme phenotypes.

For example flower colour in mirabilis jalapa.

2. False

Second statement is incorrect with respect to codominance. In case of codominance, there are two alleles both of which are equally dominant to one another. Because of this we see a variegated phenotype in heterozygotes. Variegated phenotype means it is a mixture of the two extreme phenotypes. The statement is incorrect because in codominance also, the mendelian ratios are modified and not typical.

For example ABO blood group in human beings.

3. True

The given statement is correct because pleiotropy also results in Lethal alleles. When a specific combination of alleles is formed, it can also be Lethal. These Lethal alleles die at an early stage of development and hence the mendelian ratio in adult progenies is modified.

For example coat colour in Mouse.

According to guidelines, I can answer only first question.

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