2. If purple (P) is dominant to white (p) and axial (A) is dominant to terminal

Question

2. If purple (P) is dominant to white (p) and axial (A) is dominant to terminal (a), and in a cross of white, axial to purple, axial the ratio of offspring is

6/16 white, axial;
2/16 white, terminal;

6/16 purple, axial; 2/16 purple, terminal,

then what is the genotype of the parents?

3. In a cross of two flies +/vg Cy/+ +/se +/ab X +/vg +/+ se/se ab/ab what proportion of the offspring will be mutant in phenotype for all four markers?

4. Mating of two organisms produces a 1:1 ratio of phenotypes in the progeny. The parental genotypes are?

5. Color blindness is X-linked recessive and blood type is autosomal. If two parents who are both Type A and have normal vision produce a son who is color blind and type O, what is the probability that their next child will be a female who has normal vision and is type O?

6. scalloped (sd) is an X-linked recessive and ebony (e) is an autosomal recessive mutation. What proportion of scalloped, ebony females (relative to whole population) is expected in the F2 starting with a true breeding scalloped female which is wild type for ebony mating with a true breeding male mutant only for ebony?

Explanation / Answer

2. The genotype of white,axial can be: ppAa or ppAA

The genotype of purple,axial can be PpAa or PPAa or PpAA or PPAA

After making punnett square for each one of the combinations we will match the results with the ratios given to us. Based on the given data the genotype of the parents will be:

ppAa X PpAa

3. For the given cross the proportion of the offspring will be mutant in phenotype for all four markers will be 1/32.

4. Assuming the dominant trait to be A and the recessive trait to be a, phenotype of 1:1 will be observed in the progeny with parents having genotype Aa X aa.

5. It is given that both the parents have type A blood group and their first child has O blood group therefore, we know that both the parents are heterozygous for blood type A i.e. the genotype is IAIO. Now the chance that both the parents will give the recessive allele IO for next child will be 1/2 X 1/2 = 1/4

The chance of their next child to have normal vision is 1/1. And the chance that their next child is a girl is 1/2.

Now calculating the probability of their next child to be a girl with normal vision and Type O blood group,

= 1/2X 1 X 1/2

= 1/8

Thus the probability is 1/8 for such offspring.

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