Question
Sturtevant's detailed mapping studies of the X chromosomes of Drosophila established what genetic principles? A. That genes are arranged in a linear order on the chromosomes. B. That genes are carried on chromosomes. C. That sex determination is controlled by the X and Y chromosomes. D. That segregation of an allelic gene pair is accompanied by disjunction of homologous chromosomes. E. That different pairs of chromosomes assort independently. The pairwise map distances for four linked genes are as follows A-B = 22 map units, B-C = 7 m map units, C-D = 9 map units, B-D = 2 map units, A-D=20 map units, A-C = 29 map units. What is the order of these four genes? A. ABCD B. ADBC C. ABDC D. BADC E. CADB The measured distance between genes D and E in a two point test cross is 50 map units. What does this mean in physical terms? A. D and E are on different pairs of chromosomes B. D and E are linked and exactly 50 units apart C. D and E are linked and at least 50 map units apart D. either D and E are on different pairs of chromosomes or D and E are linked and exactly 50 map E. either D and E are on different pairs of chromosomes D and E are linked and 50 map units A. Sturtevant proposed that the percentage of recombinant types resulting from a cross involving linked gen could be used as a measure of the distance separating the genes on a chromosome. A. True B. False A wild type fly is heterozygous for sable eyes, grey body, and short bristles. It is crossed to a male fly homozygous for sable, grey and short. The following progeny phenotypes were observed: sable, grey, short 400 wild type 425 sable 60 grey, short 62 sable, short 22 grey 23 short 3 sable, grey 5 Which of the following has the co gene order and map distance? A. sable-short-grey, with sable and short separated by 13 map units and short and grey separated by 5.3 map units B. sable-short-grey, with sable and short separated by 5.3 map units and short and grey separated by 13 map units C. short-grey-sable, with short and grey separated by 4.5 map units and grey and sable separated by 122 map units D. short-grey-sable, with sort and grey separated by 12.2 map units and grey and sable separated by 4.5 map
Explanation / Answer
1) That genes are arranged in a linear order on the chromosomes.
2) option B. ADBC.
3) option E. either D and E are on different pairs of chromosomes or D and E are linked and at least 50 map units apart.
4) option A. true.
5) option A. sable-short-grey, with sable and short separated by 13 map units and short and grey separated by 5.3 map units.