Question

4.

In the diploid roundworm Arronax, the Dpy gene, which is on the extreme right end of chromosome I, has two alleles: a dominant wild type allele (D) and a recessive dumpy (short and fat) allele (d). On the extreme left end of chromosome I is the twister gene with a dominant wild type allele (T) and a recessive twisted(corkscrew body) allele (t). Arronax has the curious property that each pair of homologous chromosomes undergoes exactly one recombination event per meiosis (no more, no less). You cross a wild type worm that is heterozygous for both loci (dominant alleles linking in cis) to a worm that is dumpy and twisted.The progeny will be:

A.

All dumpy and twisted

B.

All normal

C.

½ dumpy twisted and ½

wild type

D.

¼ dumpy twisted, ¼ wild type, ¼ dumpy and ¼ twisted

E.

3/4 dumpy twisted, ¾ wild type, 1/8 dumpy, 1/8 twisted

Answer 1

Answer:

C.

½ dumpy twisted and ½ wild type

Explanation:

DT/dt (heterozygous for both loci) x dt/dt (dumpy, twisted) ---Parents

The two genes are linked. It means that DT/dt genotype produces only two types of gametes, Dt & dt in equal (50%) proportion.

	dt
DT	DT/dt (wild type)-50%
dt	dt/dt (dumpy, twisted)-50%