Question

Please show how to do that with type. Thank you.

Section One: Population Genetics Biologists define evolution as changes in the frequency of genes in a population's gene pool through time. Reduced to fundamentals, that is what evolution is! Just as a canyon is the sum total of all the small buckets of dirt eroded away by a river, so organic evolution is the accumulated change in genes that carry the instructions for building organisms. To work with evolution, we must learn how to work with gene frequencies. If you understand the genetic principles discussed in Exercise One, this new material on population genetics should be easy for you. At least be certain you understand segregation and independent assortment before attempting to work at this new level. We will confine our attention to the simplest possible case: a characteristic for which there is only two pair of alleles in the population. We will call these alleles B and b. As an example, consider coat color in certain rats. The gene B produces brown fur; b is recessive to B and produces white fur. There is dominance between these two alleles with brown dominant over white. A cross between two brown heterozygous rats produces the classic 3/4 brown, 1/4 white Mendelian ratio. [To review, try these problems: (a) suppose the cross was between a heterozygous brown rat and a white rat. What kinds of offspring (genotypes and phenotypes) should this cross produce? (b) Suppose you cross two heterozygous rats and one of their offspring is brown. What is the probability that the brown offspring is heterozygous?) (Answers: (a) 1/2 Brown BB, 1/2 white bb. (b) 2/3.)

Answer 1

Given B is dominant over b .

A) cross between heterozygous brown rat( Bb) and white rat ( bb)

Parents Bb ×. bb

F1:- Bb. Bb. bb. bb.   

So we obtain Bb :- 50% or 1/2 , phenotype :- coat colour brown.

And. bb :- 50% or 1/2 , phenotype:- coat colour white.

B)cross between heterozygous brown coat rat (Bb)

Parents. Bb. ×. Bb.

F1 offsprings :- BB. Bb. Bb. bb

So we have genotype BB :- 1/4 or 25%. genotype. Bb :- 2/4 or 50%. genotype. bb :- 1/4 or 25%

Phenotype brown is Given by BB, Bb genotype. And genotype bb gives white coat rat .

For brown coat colour BB is homozygous where as Bb is heterozygous . Out of three genotype which gives brown coat colour two are heterozygous , so the possibility that the brown offspring are heterozygous is 2/3 .