Study Guide 5 Linkage Mapping Flashcards
You have isolated three new recessive mutations in Drosophila: green-eye (g), fuzzball (f), and crooked wing (c).
You cross homozygous parents to create several heterozygous F1s with genotype GgFf, GgCc, and GgFfCc.
A GgFf x ggff cross reveals the following gamete frequencies: 39% GF, 11% Gf, 9% gF, and 41% gf.
A GgCc x ggcc cross reveals gamete frequencies of 49% GC, 2% Gc, 2% gC, and 47% gc.
Do these crosses suggest that the F and C genes are linked? Explain your answer
Yes. The crosses first determine if G and F are linked and then if G and C are linked. If these genes were unlinked, we would expect the resulting offspring ratios to be even. The offspring ratios are very uneven in both crosses, meaning that genes G and F are linked and genes G and C are linked. This then means that all three genes are on the same chromosome, indicating that F and C are also linked.
You are studying four recessive mutations in Drosophila: little wing (l), maroon body pigment (m), giant antennae (g), and big eye (b). You cross homozygous parents to create several heterozygous F1s with genotype LlMm, LlGg and MmGg.
Crosses between the F1 individuals and homozygous recessive individuals (ex: LlMm x llmm) indicate gamete production in the following frequencies
a. Which of the four genes you are studying are linked?
Genes L and M are linked and genes G and B are linked, which you can tell because their gamete frequency is uneven. If genes are unlinked, we expect their distribution into gametes to be roughly even (like genes L and G, which are unlinked). Given this information, we can also determine that genes M and B are unlinked (because M is on the same chromosome as L, and G is on the same chromosome as B and we know that L and G are on different chromosomes)
You are studying four recessive mutations in Drosophila: little wing (l), maroon body pigment (m), giant antennae (g), and big eye (b). You cross homozygous parents to create several heterozygous F1s with genotype LlMm, LlGg and MmGg.
Crosses between the F1 individuals and homozygous recessive individuals (ex: LlMm x llmm) indicate gamete production in the following frequencies
b. Of the genes that are linked, which are closest together on the chromosome?
The closer together two genes are on a chromosome, the less frequently we will see their alleles be separated by recombination. Alleles from genes G and B are inherited together more frequently (their gamete frequencies are more uneven) than alleles from genes L and M, meaning that genes G and B are closer together on the chromosome than genes L and M.
