1) In the diagram below, the red arrow indicates that the male flies shown have
ID: 78367 • Letter: 1
Question
1) In the diagram below, the red arrow indicates that the male flies shown have been mutagenized with X-rays. These mutagenized males are each mated to a wild-type female. Only one F1 fly is shown in A) and another in B) (F1 progeny are in pink boxes). M (in red) denotes a phenotypically detectable, dominant mutation; m (in red) denotes a recessive mutation.
You can expect: (PLEASE SELECT ONE ANSWER)
2) Suppose you mate the mutagenized male with a female that is heterozygous for the cross-over suppressive (C), recessive lethal (l), Barr (B) = ClB “balancer” X chromosome (instead of to a wt female). You will generate F1 progeny in the frequencies shown (The X-chromosomes from the C1B/X female parent are colored red). The Y chromosome carries only a few genes. We are interested in X-linked mutations.
What is the phenotype of the flies (among these progeny) that will carry the mutant X chromosome intact (no cross-overs betweeen WT and mut chromosome) and will generate progeny with mutant phenotypes when back-crossed to WT flies? (PLEASE SELECT ONE ANSWER)
a) All of the F1 progeny will carry mutations that affect eye color (the phenotype you are following) b) Each F1 fly will likely carry a unique mutation(s) distinguishing it from other F1 flies c) All F1 flies with mutations will carry dominant mutations d) Only male F1 flies will carry mutations A)", E: ) +++la -+IWT :F1 xL301 ttt^-+ | F1 0+ B ? A-10LExplanation / Answer
Answer
1. The mutation in the male flies with X-ray produced offspring with a phenotypically detectable, dominant mutation;M (in red) and a recessive mutation m (in red). Then in the F1 genration, each F1 fly would receive a mutated gene and each offspring would be different from the other . This is becuase, the mutanized fly will pass o the mutant sperm that aare equally likely present on the X chromosomes and Y chromosome as well. Therefore, each F1 fly will carry a unique mutation and each fly would differe from one another.
Hence, the correct answer is option (b). Each F1 fly will likely carry a unique mutation(s) distinguishing it from other F1 flies.
2. In the second cross, the mutagenized male is crossed to heterozygous female with ClB “balancer” X chromosome. When no crossover is observed, the intact X chromosome is inherited by Barr - eyed females. This is because females contain XX chromosomes and one of the X chromosomes would be intact resulting in heterozygous genotype encoding for Barr eyes in females.
Hence, the correct answer is option (c). Barr-eyed females.
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