In the yawncat (a rare hypothetical animal), the dominant allele R causes solid
ID: 144110 • Letter: I
Question
In the yawncat (a rare hypothetical animal), the dominant allele R causes solid tail color, and the recessive allele r results in white spots on a colored background. The black coat color allele B is dominant to the brown allele b, but these genes can only be expressed if the animal has an mm genotype at a third gene locus. Animals that are M- are yellow regardless of which allele from the B locus is present. A mating between a solid yellow-tailed male yawncat and a solid brown-tailed female yawncat produce 16 offspring with the following tail phenotypes: six solid yellow, two spotted yellow, three solid black, one spotted black, three solid brown, and one spotted brown.
a. What are the most likely genotypes of the male and female parents? Explain the strategy used to determine the genotypes.
b. What is the probability of the next offspring having a solid brown tail?
Explanation / Answer
Solid Tail (R) > Spotted Tail (r)
Solid Tail genotypes = RR, Rr, rR
Spotted Tail genotypes = rr
Black-coloured Tail (B) > Brown-coloured Tail (b)
Disc-shaped genotypes = BB, Bb, bB
Sphere-shaped genotypes = bb
Expressed only when mm
Not for MM, Mm, or mM
Answer a.
Firstly, we look at the solid tail, spotted tail concept.
There are 12 offsprings with solid tail while there are 4 with spotted.
This is a clear indication that both the parents are heterozygous for the trait.
Tentative Genotypes of the parents:
Heterozygous Solid Tail Father = Rr
Heterozygous Solid Tail Mother = Rr
When it comes to tail-colour, 8 of the 16 offsprings are able to express Black or Brown colour, while remaining 8 only give yellow, this kind of half-half pattern suggests that one parent has to be homozygous recessive for mm while the other has to be heterozygous dominant Mm.
Also, since the 8 Black or Brown offsprings obtained are equally 4 each, we get the same reiteration, and this kind of half-half pattern suggests that one parent has to be homozygous recessive for bb while the other has to be heterozygous dominant Bb.
As per Mendelian Laws of Inheritance (Segregation, Independent Assortment, and Dominance):
Most-likely genotypes of the parents: BbMmRr & bbmmRr
Answer b.
.Probability of the next offspring having a solid brown tail = 3/16