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Genetics problem set

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1. Diagram the process of meiosis using the four chromosomes given below.

2. A father has dimples, the mother does not have dimples, and one of their three children have dimples but the other two do not. Dimples (D) are dominant over no dimples (d). Give the probable genotypes of all five persons concerned.

3. Explain the process you would use to tell if an F2 seed that appeared to have the dominant phenotype was homozygous dominant or heterozygous.

4. Both the husband and wife have normal vision. The wife gives birth to a color-blind daughter. What can you deduce about the girl's parentage? Explain why.

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1. Diagram the process of meiosis using the four chromosomes given below.

Meiosis is the process by which gametes are formed. Unlike in mitosis 4 haploid cells are produced. However, the parts of the cycle are the same albeit slightly different. In our imaginary cell with 4 chromosomes (A1, A2, B1, B2) the letters indicate homologous chromosomes.

Meiosis I
S phase- the DNA content of the cell is duplicated.
A1,A2,B1,B2 -----> A1,A1,A2,A2,B1,B1,B2,B2

Prophase I- nuclear envelop break down occurs and chromosomes condense.

Metaphase I- homologous chromosomes line up on the metaphase plate.
A1A1A2A2
B1B1B2B2

Anapahse I- homologous chromosomes move towards opposite poles.
A1A1 A2A2
B1B1 B2B2

Telophase I- homologous chromosomes are segregated to opposite poles.
A1A1 A2A2
B1B1 B2B2

Cytokinesis I- cell division occurs.

Meiosis II
Daughter cells divide again ...

Solution Summary

Detailed answers with references for 4 questions regarding inheritance of dominant negative alleles.

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Mendelian Genetics Problem Set is solved.

1. A cattle rancher discovers that one of his bulls has a great deal of muscle mass but little fat, and wishes to create a pure-breeding stock with that trait. When he breeds the bull with wild-type cows, all of the offspring are wild-type. How can the rancher create his pure stock if the allele for lean muscle is autosomal?

2. The same cattle rancher has a bull that is unusually docile and wishes to create a pure-breeding stock with that trait. When he breeds the bull with wild-type cows, all of the calves are wild-type. How can the rancher create his pure stock if the allele for tameness is sex-linked?

3. A woman with AB blood type marries a man who has type A.
--What are all the possible blood genotypes that their children could have? Remember that you don't know if he is AA or AO.
--How could you find out his genotype by:
a. Studying their children's blood phenotypes?
b. Studying his (the father's) ancestors' blood phenotypes?

4. A scientist notices that the fish that she is studying come in 3 colors. when she breeds two yellow fish, all of the offspring are yellow. When she breeds two blue fish, all of the offspring are blue. when two green fish are bred, 25% of the offspring are yellow, 25% are blue, and the rest are green.
--How would you describe the alleles for color in these fish?
--What would result if you bred a yellow fish with a blue fish?
--How about a green with a blue?

5. An enterprising pet store owner is attempting to create a pure strain of ultra-dwarf mice to sell as novelty pets. he breeds 10 pairs of ultra-dwarf mice and counts the different phenotypes seen in the offspring. (A wild-type mouse litter is 10 mice.) In the F1 generation, 50 are ultra-dwarf, and 25 are wild-type. Each time he breeds two ultra-dwarves he gets the same ratio.
--What is going on?
--Will he ever get a pure strain? If not, why?

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