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Genetics 303, HW 1
1)
Draw a cell with genotype AaBB as it undergoes mitosis.
2) Draw a cell with genotype AaBB as it undergoes meiosis.
3) Which kind of trait, one determined by dominant or recessive alleles, would be most easily
eradicated from a population of organisms? Why?
4) How many kinds of gametes can an individual of genotype aabbddEE produce? AaBbddEe?
5) Complete a monohybrid cross Aa x Aa and sort by predicted genotypic and phenotypic ratios.
6) Complete a dihybrid cross AaBb x AaBb and sort by predicted genotypic and phenotypic ratios.
7) Complete a trihybrid cross AaBbDd x AaBbDd and sort by predicted genotypic and phenotypic ratios.
8) A cell in G1 of interphase has 12 chromosomes. How many chromosomes and DNA molecules will be
found per cell when this original cell progresses to the following stages?
a) G2 of interphase
b) Metaphase I of meiosis
c) Prophase of mitosis
d) Anaphase I of meiosis
e) Anaphase II of meiosis
f) Prophase II of meiosis
g) After cytokinesis following mitosis
h) After cytokinesis following meiosis II
9) Parents with the genotypes AABb x Aabb mate. What is P(Aabb offspring)?
What is P(aabb)?
What is P(offspring with AA or bb genotype)?
10) In parakeets, two non-linked autosomal genes control the production of feather pigments. Gene B
controls the production of blue pigment, and gene Y controls the production of yellow pigment.
Known recessive mutations in each gene result in the loss of pigment synthesis. Two green
parakeets are mated and produce green, blue, yellow, and albino progeny. Hint: To solve this
problem, you should try to draw these in a pathway.
(a) Based on this information, explain the pattern of inheritance. Be sure to include the
genotypes of the green parents and all four phenotypic classes, as well as the fraction of the
total progeny that each phenotypic class represents in your answer.
Genetics 303, HW 1
(b) The parental (green) parakeets are the progeny of a cross between two true-breeding
strains. What two types of crosses between true-breeding strains could have produced the
green parents? Indicate the genotypes and phenotypes for each strain.
11) In some plants, a red pigment, cyaniding, is synthesized form a colorless precursor. The addition of
a hydroxyl group (-OH) to the cyaniding molecule causes it to become purple. In a cross between
two randomly selected purple plants, the following results are obtained. 94 purple: 31 red : 43
colorless.
a)
How many genes are involved in determining these flower colors? Which genotypic
combinations produce which phenotypes? Diagram the purple x purple cross.
b) Predict the outcome (both genotypically and phenotypically) of crossing the same purple
plant with a true breeding red plant.
12) In dogs there are three autosomal, independently assorting allelic pairs with the following
genotype-phenotype relationships:
B,b
Codominance; BB = black, Bb = spotted (black & tan), bb = tan
G,g
G (grey eyes) completely dominant to g (yellow eyes)
L,l
Incomplete dominance; LL = normal liver, Ll = diseased liver, ll = no liver (lethal)
In addition, the L,l allelic pair is subject to abnormal transmission ratios in males only, such that
heterozygous males transmit 70% l-bearing sperm and 30% L-bearing sperm.
a. In the cross of a female BbGgLL to a male BbGGLl, what proportion of the black, grey-eyed,
normal-livered progeny will be homozygous for all three genes?
b. Of the living progeny of the following cross, what is the probability of obtaining a spotted, greyeyed, normal-livered puppy?
BbGgLl female x bbGgLl male
13) What is the difference between a tumor suppressor gene and a oncogene? What effects do each of
these have on cells. Give an example of each type of gene.
Genetics 303, HW 1
14) What is p53 and what does it do?
15) Given the following F2 phenotypic ratios, deduce the expected phenotypic ratios for the testcross of
the F1 dihybrid.
(a) 9:3:3:1
(b) 15:1
(c) 9:3:4
(d) 12:3:1
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