# BBIO 053: GENETICS ASSIGNMENT

BBIO 053: GENETICS ASSIGNMENT

Give a complete solution and explanation for each problem, not just the answer. Read the question thoroughly before you begin, and make sure to express your answer in the form indicated for each question.

.1. a. Draw or model (e.g. using modelling clay) a 2n=4 cell undergoing meiosis from Prophase I to Telophase I. Be sure to represent homologous chromosomes with different colours to distinguish them. Include one crossover event.

1. Redraw/model the same sequence of events but showing the effects of independent
assortment; i.e. show when and how the chromosomes might be arranged differently that
would lead to a correct but different outcome in the chromosomes in the daughter cells of

1. In humans, brown eyes are usually dominant over blue eyes. Suppose a blue-eyed man marries a brown-eyed woman whose father was blue-eyed. What proportion of their children would you predict will have blue eyes?

B       b

b    Bb    bb                    50% of their children will have blue eyes

b     Bb    bb                    Geno: Bb  : bb  Pheno:  Brown: blue

1. A dog breeder has two black labs that he breeds every year. He takes careful records of the colors of offspring produced from the breeding. Over an eight year period, he has recorded 19 chocolate pups and 62 black pups. What colour is dominant, and what are the probable genotypes of the two parents? Show the cross to prove it.

In the entire period, no yellow pups have been produced which means parents does not contain allele e, and there are both chocolate and black pups so parents must be heterozygous for B that is Bb,

1. In Australian Shepherds, there are several variations in markings, but the underlying coat colours either black or red, where black is dominant to red. A breeder wishes to gradually convert her breeding program so that her dogs only ever produce black pups (i.e. she wants pure breeding black dogs).

How can she do this? Give full explanations and sample outcomes of crosses to assist with your
explanation.

1. In mice, the genotype yy produces grey coat colour, Yy gives yellow and YY causes the embryo to die a few days after conception (before birth).
a. What offspring would be expected from a cross between a yellow mouse and a grey
one?
2. Between two yellow mice?
3. Which of these crosses would likely produce the largest litter?

1. Two short-tailed cats are mated, and the litter that results contains three kittens without tails, two with long tails and six with short tails.
2. What kind of dominance is most likely involved in determining tail length in these cats? incomplete dominance.
3. Show all genotypes and their corresponding phenotypes for this trait. Short tails are heterozygous (Tt), long tails are homozygous (TT) and no tails are homozygous (tt).

1. What would the result be if a cat with no tail was mated with a short-tailed cat?
t    t   ( no tails)

(short tails)   T   Tt  Tt

t   tt      tt

50% chance it would have a short tail

1. The X chromosome of a cat carries a gene that codes for deafness when recessive. A female cat that is heterozygous for deafness is crossed with a male cat that is not deaf. Show the cross. What are the phenotypes of the offspring and in what proportions? XBD XBd x XbD Y

 XBD XbD female XBd XbD female XBD Y Black male XBd Y Black, deaf male

1. In some breeds of cattle, coat colour is determined by a codominant gene, where red fur andwhite fur are the alternate alleles for the colour. When the genotype is heterozygous, the animal has both red and white hairs in its fur, so the colour appears light red, and is called roan.
2. What would be the phenotypic ratios of the offspring if you breed two roan cattle?
3. What are the ratios if you breed a red cow with a white bull?

1. Suppose a father and mother claim they have been given the wrong baby at the hospital. Both parents are blood type A. The baby they have been given is blood type O. Use what you know about the inheritance of blood type to show if this fact provides evidence to support the parent’s claim.
We know the parents phenotypes but not their genotypes. It is possible that both parents are heterozygous (IA i ). Which would be possible to produce a type O child 25% of the time so the baby could still belong to these parents

1. The pedigree below traces the inheritance of alkaptonuria, a biochemical disorder. Affected individuals, indicated here by the filled-in circles and squares, are unable to break down a substance called alkapton, which colors the urine and stains body tissues.

1. According to the pedigree below, does alkaptonuria appear to be caused by a
dominant or recessive allele?
recessive

1. Fill in the genotypes of the individuals whose genotypes you know, and the possible genotypes for the other individuals