Exam 3: The Chromosome Theory of Inheritance

Suppose an individual is heterozygous for two linked pairs of alleles on the same chromosome arm,Ab/aB such that the A locus is closer to the centromere than the B locus.Under what conditions would a crossover in a somatic cell generate a twin spot,i.e. ,two adjacent clones of cells,one clone homozygous for a and the other clone homozygous for b?

The pairwise map distances for four linked genes are as follows: A-B = 22 m.u. ,B-C = 7 m.u. ,C-D = 9 m.u. ,B-D = 2 m.u. ,A-D = 20 m.u. ,A-C = 29 m.u.What is the order of these four genes?

What happens physically during the process of crossing over?

In peas,tall (T)is dominant to short (t),red flowers (R)is dominant to white flowers (r),and wide leaves (W)is dominant to narrow leaves (w).A tall,red,wide-leaved plant is crossed to a short,white,narrow-leaved plant and the progeny are as follows: tall red wide 381 tall white wide 122 short red wide 118 short white wide 379 1000 Give the linkage arrangements.

C.Stern studied recombination between two homologous X chromosomes in Drosophila in which one chromosome had two cytologically visible abnormalities at opposite ends.What did he find?

Observation of which of the following led to the discovery of mitotic recombination?

Females heterozygous for the recessive second chromosome mutations pn,px,and sp are mated to a male homozygous for all three mutations.The offspring are as follows: pxspcn 1,461 pxsp+ 3,497 px+cn 1 px++ 11 +spcn 9 +sp+ 0 ++cn 3,482 +++ 10,000 What is the genotype of the females that gave rise to these progeny?

In Drosophila,the genes b,c,and sp are linked and in the order given,the distances being b-c = 30 m.u.and c-sp = 20 m.u.These intervals exhibit 90% interference.How many double crossovers would be recovered in a three-point cross involving b,c,and sp out of 1000 progeny?

Crossing over takes place in paired bivalents consisting of ______ chromatids,and involves _______ of the chromatids.

What is a testcross?

The map of a chromosome interval is A-10 m.u.-B-40 m.u.-C.From the cross Abc/aBC × abc/abc,how many double crossovers would be expected out of 1000 progeny?

In fruit flies,the recessive pr and cn mutations cause brown and bright-red eyes,respectively (wild-type flies have brick-red eyes).The double mutant pr cn combination has orange eyes.A female who has wild-type eyes is crossed to an orange-eyed male.Their progeny have the following distribution of eye colours: wild-type 8 brown 241 bright-red 239 orange 12 500 What is the map distance between the pr and cn genes?

Females heterozygous for the recessive second chromosome mutations pn,px,and sp are mated to a male homozygous for all three mutations.The offspring are as follows: pxspcn 1,461 pxsp+ 3,497 px+cn 1 px++ 11 +spcn 9 +sp+ 0 ++cn 3,482 +++ 10,000 Calculate the coefficient of coincidence and comment on its meaning.

A dihybrid test cross is made between the genes C and D with the following results.Calculate ?² to test the hypothesis that the C and D genes are unlinked. CcDc\timesccdd CD 222 Cd 280 cD 280 cd 218 1000

In humans,the genes for red-green colour blindness (R = normal,r = colour-blind)and haemophilia A (H = normal,h = haemophilia)are both X-linked and only 3 map units apart.Suppose a woman has four sons,and two are colour-blind but have normal blood clotting and two have haemophilia but normal colour vision.What is the probable genotype of the woman?

By definition,a tester is always

In Drosophila,the genes y,f,and v are all X-linked.y f v females are crossed to wild-type males and the F₁ females are test-crossed.The F₂ are distributed as follows. yfv 3210 yf+ 72 y+v 1024 y++ 678 +fv 690 +f+ 1044 ++v 60 +++ 10,000 Calculate the coefficient of coincidence.

In Drosophila,the genes y,f,and v are all X-linked.y f v females are crossed to wild-type males and the F₁ females are test-crossed.The F₂ are distributed as follows. yfv 3210 yf+ 72 y+v 1024 y++ 678 +fv 690 +f+ 1044 ++v 60 +++ 10,000 Determine the linkage arrangement of these three genes and calculate the map distances.

The T/t and S/s genes are linked and 10 map units apart.In the cross Ts/tS × ts/ts what fraction of the progeny will be Ts/ts?

Abnormal chromosomes used by Stern and others to study crossovers are called