1) (8 point question) Panel A shows the initial crosses and representative chrom
ID: 167053 • Letter: 1
Question
1) (8 point question) Panel A shows the initial crosses and representative chromosomes of animals in a QTL mapping project for body size. 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 largest animals from two different populations that were created for QTL mapping. From left to right the homologous chromosomes pairs are 1, 2, and 3.
a) (3 points) Panels B and C are representative of animals from the first QTL mapping population. D and E are representative of animals from the second QTL mapping population. Explain the difference between the two approaches used for QTL mapping in these two experiments.
b) (2 points) Which mapping population would be faster to breed. The population that includes B & C or the population that includes D & E? Explain your reasoning.
c) (3 points) The chromosomes in panels B-E represent the largest animals from their respective populations. Which chromosomes are most likely to have genes that affect body size? Indicate with an X on the chromosomes on the bottom the potential location/s of QTL's. Explain your reasoning.
2) (7 point question) Two different purebred lines of squash have mean fruit sizes of 3 kg and 1 kg respectively. A cross between these two plants will produce an F1 hybrid that has a mean fruit size of 2 kg.
Progeny from a self of the F1 hybrid grown in strictly controlled environmental conditions will lead to F2 progeny with fruit sizes that range from 1 to 3 kg. From two hundred F2 progeny only three are found to weigh about 1 kg and only three are found to weigh about 3 kg.
a) (2 points) Estimate the number of genes that are involved for controlling this trait in the two varieties. Show your calculations.
b) (2 points) Estimate how much weight does a single additive allele of these genes contribute to the phenotypes observed.
c) (3 points) How can two squash plants from the F2 progeny, both with fruit of moderate weight, produce progeny with fruit that are much larger than either of them when crossed? (Assume there is a negligible difference in the environment for this part of the question)
Pure line A Pure line B go UUExplanation / Answer
Answer 1)
a)
In first QTL mapping population, exchange of homologous segments of DNA has occurred simply by crossing over.
On the other hand, in second QTL mapping population, the homologous segments have not been exchanged. Infact transposition of segments has occurred. Transposition along with deletion has occurred, resulting in deletion of light colored DNA segment.
b)
The first QTL mapping population is giving heterozygous population, which is easier to breed. On the other hand, the second QTL mapping population is giving a homozygous population. It is very difficult to breed and maintain homozygous populations.
c)
It has been given that from left to right the homologous chromosome pairs are 1, 2, 3 and 4 (Please note: ‘4’ is not given, but it is understood).
As per diagram of the parents, the black colored segments and chromosomes are responsible for body size. All chromosomes are having black colored segments, so, all chromosomes are having genes that affect body size.
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