exam 1

Topics: Gene, DNA, Classical genetics Pages: 11 (2135 words) Published: October 17, 2014
Study4Finals: Bio 97 ADL 10 & ADL 11 Homework - Google文档

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Study for Bio 97 Notes for Finals (ADL HW 10)
Item #1

Recombination occurs when combinations of alleles not found in either parent are placed into gametes during meiosis in the F generation. The F can be thought of as having been formed 1
1
from two haploid “input” gametes.
In this case, the F is a dihybrid with AB on one chromosome and ab on the other 1
chromosome. You can tell this by looking at the parents. The F1 hybrid got AB from one parent and ab from the other parent (AB/ab). A dihybrid that is AB/ab can produce four possible “output” gametes through meiosis. Output gametes that match one of the input gametes are nonrecombinant (AB or ab). Output gametes with new combinations of alleles are recombinant (Ab or aB).

Its important to realize that its also possible to have a dihybrid who is Ab/aB instead. In this case, one parent was AAbb and the other parent aaBB. A dihybrid who is Ab/aB can also produce four possible "output" gametes through meiosis, but in this case the nonrecombinant

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Study4Finals: Bio 97 ADL 10 & ADL 11 Homework - Google文档

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gametes are Ab or aB and the recombinant gametes are AB or ab. In Part C, be sure to check the parents of the F1 trihybrid to determine their configuration of alleles before answering the question. Which gametes are nonrecombinant versus recombinant depends how the alleles are organized in the F1 trihybrid.

In a testcross with a homozygous recessive line (tester), the tester will contribute only recessive alleles that do not affect the F phenotypes. Therefore, such testcrosses allow you to 2
determine the haploid genotype of the gametes produced by the F dihybrid. 1

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Part D - Mapping with trihybrid (three-point) testcrosses
You examine 450 progeny from the cross in Part C and classify them according to phenotype. The results are shown in the table below.

Hint 1. How to calculate recombination frequencies in a three-point testcross Recombination frequency is the proportion of recombinants for a given pair of loci. For example, for the apricot and crimson loci, there are four gamete types that are recombinant (outlined in red below). The number of progeny with these gamete types divided by the total number of progeny is the recombination frequency between these two loci.

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Hint 2. How do I assemble a linkage map once I’ve calculated recombination frequencies? Consider a testcross in which you observe the following recombination frequencies: Between locus D and locus E: 15 mu

Between locus D and locus F: 5 mu
Between locus E and locus F: 18.5 mu

Correct
Follow these steps to construct a linkage map for three linked loci: 1. Place the loci with the largest recombination frequency on the outside of the map. 2. Use the two smaller recombination frequencies to determine the distances between the outside loci and the middle locus.

3. Adjust the longest map distance to equal the sum of the smallest distances, avoiding inaccuracies due to double-crossover events between widely spaced loci. Use these data to complete the linkage map shown below.

● Vertical dashes indicate the loci of the three alleles, one of which (apricot) is already labeled. ● Numbers in the white labels give the distance in map units between adjacent loci. ● Line...
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