Chapter 15 – The Chromosomal Basis of Inheritance – …
Chapter 15 – The Chromosomal Basis of Inheritance – Homework
1. Recombination frequency is given below for several gene pairs. Create a linkage map for
these genes, showing the map unit distance between loci.
j-k 12%, j-m 9%, k-l 6%, l-m 15%
2. Mendel’s law of independent assortment applies to genes that are on different homologous
chromosomes. However, two of the traits Mendel studied were actually located on the same
chromosome.
a) Explain why genes located more than 50 map units apart behave as through they are not
linked.
b) How can one determine whether these genes are linked and what the relative distance is
between them?
3. You have found a new mutant phenotype in fruit flies that you suspect is recessive and sex-
linked. What is the single, best cross you could make to confirm your predictions?
4. In guinea pigs, black (B) is dominant to brown (b), and solid color (S) is dominant to spotted
(s). A heterozygous black, solid-colored pig is mated with a brown, spotted pig. The total
offspring for several litters are: 16 black solid, 5 black spotted, 5 brown solid and 14 brown
spotted.
a) Are the genes linked? Explain
b) If the genes are linked, how many map units are they apart?
5. A woman is a carrier for a sex-linked lethal gene that causes an embryo with the gene to
spontaneously abort. She has nine children. How many do you expect to be boys?
6. A dominant sex-linked gene (B) produces white bars on black chickens, as seen in the Barred
Plymouth Rock breed. A clutch of chicks as equal numbers of black solid and barred chicks.
(Remember that sex is determined by the Z-W system in birds: ZZ are males and ZW are
females)
a) If only the females are found to be black solid, what were the genotypes of the parents?
b) If males and females are evenly represented in the black solid and barred chicks, what
were the genotypes of the parents?
7. Dr. Smith once had a female student that was color-blind. He was able to state something
immediately about the vision of her father. What was he able to say? Explain.
8. Calico kittens often sell at a higher price than non-calico kittens. If you were a cat breeder,
what parents would you cross together to maximize your profit?
9. As a cat breeder, you are contacted by a person who offers to sell you a male calico to use in
your breeding program. Would this be a good investment for your business? Explain.
10. Women who are carriers for color-blindness usually have patches of color-blind areas on
the retinas (the area at the back of the eye that receives light). Explain.
11. Explain Mendel’s Law of Segregation through the Independent Assortment of Chromosomes.
12. Neither Steve or Ruth are have hemophilia, but their firstborn son does have it. What is the
probability that a second child of this couple will have the condition? What is the probability if
the second child is a boy? A girl?
13. More common than completely polyploidy animals are mosaic polyploidy animals that are
diploid except for patches of polyploidy cells. How might a mosaic tetraploid animal arise?
14. About 5% of individuals with trisomy 21 are Robertsonian translocations where a partial copy
of chromosome 21 is attached to chromosome 14. Do these individuals have 46 or 47
chromosomes? Explain. Can this translocation and trisomy condition be passed on to kids?
Explain
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