The R and Y genes are 15 maps unit from each other on chromosome 2. A botanist sets up a parental cross between a true breeding yellow flowered plant with red tomatoes and a plant that is true breeding, double-recessive for the Y and R genes. What are the expected frequencies of the recombinant and parental gamete genotypes produced by the F1 plants? Choose all correct answers. The total percentage of gametes with recombinant genotypes will be 15%. Each recombinant gamete genotype will be produced 7.5% of the time. The total percentage of gametes with parental genotypes will be 100%. Each recombinant gamete genotype will be produced 25% of the time. Each parental gamete genotype will be produced 50% of the time. The total percentage of gametes with recombinant genotypes will be 50%. The total percentage of gametes with parental genotypes will be 85%. Each parental gamete genotype will be produced 42.5% of the time.

Answer options:

Answer

Explanation:

Map units are an arbitrary measurement based on the number of recombinants in a cross. Alleles on the same chromosome can only be inherited separately if crossing over occurs between them (i.e. genetic material is exchanged between different chromosomes).

The closer genes are together on a chromosome the less likely this is to occur and therefore the fewer number of recombinant phenotypes will be present.

Recombinant phenotypes are those that do not match the parents, i.e. a plant with non-yellow flowers and red tomatoes or yellow flowers and non-red tomatoes. If they are 15 map units apart, that means recombinant phenotypes when crossing 2 heterozygous individuals (F2 generation) only occur 15% of the time.

This cross is between  2 true breeding plants: YYRR x yyrr

The first parent can only produce YR gametes, and the second parent can only produce yr gametes.

Therefore, all the F1 offspring will be YyRr

The potential gametes for the F2 generation are YR, yr, Yr, yR. However, we know that Y and R are fairly close on the same chromosome. 15 map units apart means they only recombine to give yR or Yr phenotypes 15% of the time.

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