Series 2: The genetic basis of traits

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Answer the questions below; you will receive a confirmation of your submission. Some questions may have several correct answers. You will receive the maximum number of points if you identify all of the (and only the) correct answers.

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1: A man has sickle cell anaemia, while his wife is a carrier (but does not have the disease herself). Which of the following statements are true?

4 points

All of their offspring will have the disease.

Any one of their offspring will either have the disease or will be a carrier.

The couple has two offspring. If one of these offspring has the disease, then the other offspring must be disease-free.

Their grandchildren must have the disease.

2: Now consider a situation where the man has Huntingdon's disease, while the woman is disease-free. Which of the statements are correct now?

4 points

All of their offspring will have the disease.

Any one of their offspring will either have the disease or will be a carrier.

The couple has two offspring. If one of these offspring has the disease, then the other offspring must be disease-free.

Their grandchildren must have the disease.

3: Suppose we sequence the man and find that he is homozygous for the allele that causes Huntington's disease. Does this change your answer to question 2?

2 points

Yes

Clear selection

4: Look at the following pedigree. Squares represent males, circles females. Black symbols represent individuals with a particular trait. Female A had 4 daughters (C, E, F, H) and one son (J) with male B. What can you say by looking at this pedigree? Assume that no new mutations appeared in this family.

5 points

The trait is dominant.

Individual C is a carrier.

Individual G is a carrier.

We don't know if K and L are carriers.

The male in the first generation is a carrier of the trait.

5: Oculocutaneous albinism is a recessive disease, with the affected gene lying on chromosome 11. A healthy man, the son of two healthy parents, has a sister affected by this disease. He marries a woman with albinism. What can you say about this man's family?

5 points

The man is a carrier of albinism.

The parents of this man are carriers.

All of this man's children will have albinism.

All of his sister's children are carriers, or have the disease.

Whether his children have the disease or not also depends on the genotype of his spouse.

6: A breeder of rabbits decides that he wants to have all of his rabbits white (recessive trait) with floppy ears (dominant trait) [The true genetics behind bunny ears is actually more complex and not yet fully understood.]. He selected all white rabbits with floppy ears and let them mate for two generations. Which of the following scenarios are possible in the following generations?

5 points

In the first generation of offspring, all rabbits are white.

In the second generation of offspring, some rabbits are white, and some brown.

In the second generation of offspring, some rabbits have floppy and some normal ears.

In the second generation, the breeder could observe 9:3:3:1 ratio of different trait combinations.

It was impossible to observe any changes in population composition after such a short time.

7: Consider four genes: W, X, Y, and Z, located on the same chromosome. Based on an experiment, scientists have estimated the probability of a crossover occurring between the pairs of genes as follows: W - X ... 19,7%; W - Y ... 60,2%; W - Z ... 48,9%; X - Y ... 41,5%; X - Z ... 29,6 %; Y - Z ... 11,5 %. How are these genes located on the chromosome?

5 points

W --- Y --- X --- Z

Y --- Z --- X --- W

Z --- Y --- X --- W

Y --- X --- Z --- W

W --- X --- Z --- Y

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