in a study of fat content in mouse milk, two inbred strains were crossed and the resultant progeny had a phenotypic variance of 4.65. when these F1 were allowed to produce an F2, the phenotypic variance for fat content increases to 5.64 in the F2. What is the value for V_e in this study? Why did the phenotypic variance increase in the F₂ generation? What is the broad sense heritability for fat content in mouse milk?

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Lelia LubowitzLv2

30 Jun 2019

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Two inbred strains were crossed. In the F1 generation, the variance of height was 12.8, and the variance of dry weight was 9.6. The F1 generation was selfed and the resulting offspring had a height variance of 26.5 and a dry weight variance of 13.9. Calculate the broad-sense heritability for both traits for the F2 generation and state which has a larger influence from genetics.

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*5. Margaret is studying a population of sunflowers that are genetically variable in a controlled lab setting. She measures the mean and variance of seed set on 1000 individuals. The phenotypic variance in seed number is 30. She picks one plant to self-pollinate and produces 200 genetically identical progeny. The phenotypic variance in seed number in these progeny is 20. Use this information to answer the questions below.

A. Calculate the broad-sense Heritability (H²)

B. What does the broad-sense heritability value tell you about the role of genetics and environment on phenotypic variance in seed number?

C. Margret has decided to leave academia and become a lawyer. She has also decided to bring her sunflowers with her and plant them in her garden. She repeats the experiment described above in her yard, and calculates an H² for seed set to be 0.90. Give two reasons why it is not surprising that this value is different from the one in part A.

D. Researchers determine that the narrow-sense heritability (h²) of seed set in sunflowers is 0.50. These researches undertake a project to increase the number of seeds produced by each plant. The mean number of seeds is currently 75. Plants with a mean of 100 seeds are interbred as parents of the next generation. What mean number of seeds can be expected in this generation?

E. If the narrow-sense heritability in sunflowers is 0.50 how do you explain how Margret calculated an H² of 0.90 for seed set in her garden?

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During the course of the infamous Drosophila experiment, two students noticed a female fly that behaved in a peculiar manner. She crawled very slowly and did not fly. Realizing that this fly, collected as a virgin female, was abnormal, they did not use her in their experiment, but decided to investigate the inheritance of this tired trait. They crossed the tired female with a wild-type male and were surprised to find that all the F1 flies, male and female, exhibited the tired trait. They allowed these flies to mate and observed that all the F2 flies were tired. They generated an F3 and F4 generation. All flies were tired. Satisfied that they had a true-breeding stock, they performed reciprocal crosses with wild type. Wild-type males by tired females yielded all tired flies in the F1 and succeeding generations. However, when tired males were crossed to wild-type females, the F1 progeny were all wild type. Succeeding generations were wild type.

A. What type of inheritance is exhibited by tired? Explain. Suggest a likely location in the cell for this mutation. Explain.

During their studies, an apparently wild-type fly, a male, appeared in one of their tired stocks. Since the fly carried several other markers, these two students concluded--after much argument--that this fly was not a contaminant. They crossed this revertant male with a tired female from the pure-breeding stock. The progeny were phenotypically 50% tired and 50% wild type. Males and females were represented equally between both phenotypes.

B. Was the mutation that produced the wild-type phenotype in the unusual male dominant or recessive? Explain. What is the most likely origin of this mutation? Explain.