1) Panel A shows the initial crosses and representative chromosomes of animals i

Question

1) Panel A shows the initial crosses and representative chromosomes of animals in a QTL mapping project. The black regions represent chromosome material from the largest purebred line and the white regions represent the other pure bred line used in the experiment. Panels B, C, D and E show the karyotypes representative of the smallest and darkest animals from populations of mice that were created for QTL mapping. Purina B Puroline A C) The chromosomes in panels B-E represent the smallest and darkest animals from their respective populations. Which chromosomes are most likely to have genes that affect the two traits? Indicate with an S (for size loci) or P (pigment loci) on the chromosomes to the right the potential location/s of all the potential QTL's. Explain your reasoning. D) Purebred line A and B are about 45 g and 15 g respectively. A cross between these two mouse strains will produce the F1 hybrid. Progeny from crosses of the F1 siblings will lead to F2 progeny with sizes that range from 45 g to 15 g. From two hundred F2 progeny only three are found to weigh about 15 g and only three are found to weigh about 45 kg. i) Estimate the number of genes that are involved for controlling this trait in these mice. Show your calculations. ii) Estimate how much weight does a single additive allele of these genes contribute to the phenotypes observed. E) The researchers document the full size for all the mice in the F2 population, but also the F1 and parental populations. Even in the inbred lines the sizes are variable (see the table for the size variance of each mouse population). What is the broad sense heritability of the size trait based on these data in the table below. Show your calculations. Pure Line A Pure Line B F1 F2 Mean 8 Variance 8

Explanation / Answer

C) According to the information, two sets of phenotypes are being observed here, body size and coat color. It must be carefully noted from the illustration that all the F1 population (the offspring obtained from the cross between pure line A and pure line B) showed a mix-breed, having a large size and dark color of the coat. However, there was mere segregation of the alleles and no crossing over of the chromosomes was visible in this case. On the other hand, the selfing of F1 provided a different set of the population where the chromosomes showed a mosaic pattern for the two phenotypes.

However, one careful observation, it can be seen that the chromosomal pair 1 and 4 tend to retain the genes most similar to the parental types. Since the panel B or pair 1 of chromosomes is representing the phenotypes for body size (small) and coat colors (dark) respectively, this suggests that the pair 1 is responsible for body size and pair 4 for the coat color.

E) What is the broad sense heritability?

In pure line A and pure line B variance is only due to environmental factors not due to genetic factors and in F1 generation variance is 22.

Total varience = varience due to environment +varience due to genetics

V= Ve+ Vg and here vg is 0 whereas in F2 varience is due to both genetic factor and environment factor

F2= vg + ve

26=vg+22

Vg= 26-22=4 and broad sense heritibality formula is vg/vg+ve  

So 4/26=0.15

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