A few practice Gene Mapping problems 1. Genetic analysis has shown that the recessive genes an ("Anther ear"), br ("brachytic") and f ("fine stripe") are all found on chromosome #1 of maize (corn). When a plant that is heterozygous for each of these markers is test-crossed with a homozygous recessive plant, the following results are obtained: Test Cross Progeny Numbers wild type 98 fine 26 brachytic 2 brachytic fine 379 anther 385 anther fine 3 anther brachytic 20 anther brachytic fine 87 Total Offspring: 1000 Analyze this data in two steps: a) Calculate recombination frequencies between each of these three pairs of genes. and b) Draw a genetic map for the location of these 3 genes on chromosome #1 of maize. Be sure to show the map distances between the loci.
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In this case, the parental types are "anther" and "brachytic fine" because they have the highest numbers (385 and 379, respectively). The recombinant types are those with significantly lower numbers, indicating crossing over between genes. Show more…
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Three-point linkage analysis Genetic analysis has shown that the recessive genes an (Anther ear), br (brachytic), and f (fine stripe) are all found on chromosome #1 of maize. When a plant that is heterozygous for each of these markers is test-crossed with a homozygous recessive plant, the following results are obtained: Test Cross Progeny Numbers: wild type - 4 (+++) fine - 48 (++f) brachytic - 400 (+br+) brachytic fine - 40 (+brf) anther - 45 (an++) anther fine - 402 (an+f) anther brachytic - 56 (anbr+) anther brachytic fine - 5 (anbrf) Total Offspring: 1000 Calculate recombination frequencies between each of these three pairs of genes. (14 marks) Draw a genetic map for the location of these 3 genes on chromosome #1 of maize. Be sure to show the map distances between each locus. (4 marks) Calculate the interference. (4 marks)
Supreeta N.
Katlin K.
1) Corn plants heterozygous for four recessive mutations c (white kernel), g (striped leaves), s (shrunken seeds) and w (waxy seeds) were testcrossed to a white, striped leaves, shrunken and waxy plant as shown: Tetrahybrid testcross: CcGgSsWw x ccggssww The following testcross offspring were obtained: Seed traits Phenotype Number Red, green, shrunken, normal CGsW 2777 White, striped, plump, waxy cgSw 2708 Red, green, plump, waxy CGSw 116 White, striped, shrunken, normal cgsW 123 Red, green, shrunken, waxy CGsw 643 White, striped, plump, normal cgSW 626 Red, green, plump, normal CGSW 4 White, striped, shrunken, waxy cgsw 3 Total number of progeny: 7000 (a) (3 pts) Draw a genetic map of the four genes and determine map distances between any linked genes. (b) (2 pts) What were the genotypes of the original pure-breeding parents that produced the heterozygous plants used in the testcross? Be specific so as to indicate any allelic linkage associations. (c) (2 pts) What is the genotype of the heterozygous plants used in the testcross? Be specific so as to indicate any allelic linkage associations. (d) (2 pts) What is the coefficient of coincidence? (e) (1 pt) What is the degree of interference?
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