18) A pea plant with the genotype PpTtGg self-fertilizes. What proportion of the

Question

18) A pea plant with the genotype PpTtGg self-fertilizes. What proportion of the offspring would you expect to have the genotype ppttgg? A)3/16 B)1/8 C)1/64 D)1/256 E)O 19) What is the evolutionary significance of the tight linkage of the three loci that code for pin vs. thrum phenotypes in wild primrose? A. It causes the flowers to have two separate species B. It means that the heterozygous genotype is never expressed C. It increases the number of alleles at each locus. D. It encourages outcrossing E. Probably none.

Explanation / Answer

Ans : C. 1/64
If we assume that all the gene pairs assort independently then while crossing PpTtGg with PpTtGg, the probability of getting a pp from PpxPp is 1/4. Similarly TtxTt and GgxGg each has a probability of 1/4 to form tt and gg respectively. Therefore, the overall probability of progeny of genotype ppttgg will be 1/4x1/4x1/4 = 1/64

Ans : E. Probably none
Pin and thrum plants differ at the S-locus. The pin plants are homozygous recessive whereas the thrum plants are heterozygous with one dominant allele and one recessive allele. The linkage group at this S-locus controls the development of the two phenotypes. Since the three loci that code for pin and thrum are very closely linked together, they are inherited together as one unit.

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