SAMPLE MIDTERM EXAM for BICD 100 Genetics ---- Prof. McGinnis

1. Indicate whether the following occur during mitosis (M), the first division of meiosis (Me1) or the second division of meiosis (Me2). In some cases a correct answer will include more than one of the above alternatives. (12 points)

a) chromatids separate at anaphase _________________
b) normally occurs in somatic cells ___________________
c) In human cells, the X chromosome separates from the Y chromosome ___________________
d) homologous chromosomes pair (synapse) during prophase ________________
e) daughter cells that result have exactly the same genetic material as the parental cell _____________
f) homologous chromosomes separate at anaphase __________________


2. A three generation pedigree is shown below for a particular human trait. (12 points)
a) What is the mechanism of inheritance of the trait? ______________________________________
b) Which persons in the pedigree are known to be heterozygous for the trait? ___________________
c) What is the probability that III.5 is a carrier for the trait? __________________________________
d) If III.6 and III.3 marry, what is the probability that their first child will have the trait? __________


3. In corn, a dominant gene (A) is necessary for seed color as opposed to colorless (a). A recessive gene (w) results in waxy starch as opposed to normal starch (W). Assume that the two genes segregate independently. Give the phenotypic and genotypic ratios expected if you subject a plant that is Aa Ww, to a test cross. (6 points)


4. A corn plant known to be heterozygous at three loci is test crossed. The progeny phenotypes and frequencies are as follows:
+ + + 455
a b c 470
+ b c 35
a + + 33
+ + c 37
a b + 35
+ b + 460
a + c 475
Give the gene arrangment, linkage relations, and map distances. Is interference occurring in the recombination process involving these loci? (14 points)


4. In the Soviet Union during the late 1940s , a politician/agronomist named Trofim Lysenko claimed that by treating adult parental plants with cold temperatures (without any selection of the adult plants so treated, i.e. they all survived), their progeny would acquire a heritable resistance to the cold. Geneticists that disagreed with him were put on trial, convicted of being Mendelian parasites, then sent to Siberia to freeze to death.
Suppose a similar Nutty Professor acquired political power in the USA, and you were put on trial for holding Mendelian ideas. Describe the experimental results, and the explanation of their significance - that you would use to convince the judge and jury that heritable changes are random, & that the exposure of an organism to a particular type of environment does not adapt the progeny of that organism for that environment. (6 points)


6. In aardvarks, long nose is dominant over short nose. Imagine that a true-breeding long-nosed aardvark is crossed with a true-breeding short-nosed aardvard, and two of their F1 progeny are interbred and have a brood of 5 baby aarvarks. What is the probability that 3 of those babies have short noses? (6 points)


7. Explain what pattern of inheritance you would expect to detect in the pedigree of a human family in which an X-linked recessive mutation was assorting. (4 points)


8. a) Do germ line mutations ever become somatic mutations? b) Do somatic mutations ever become germ line mutations? (4 points)


9. A woman of blood group AB marries a man of blood group A whose father was group O. What is the probability that: (4 points)
a. Their two children will both be group A? ___________________
b. One child will be group B and the other group O? ______________________________________


10. Two pure breeding lines of snowy white rabbits are crossed. The numerous F1 bunnies all have black fur. How do you explain this in terms of the genotypes of the parental generation? (6 points)


11. Imagine that dominant allele (B) in reindeer results in a brown nose, and allele (b) in the same gene in a red nose. If recessive alleles in the independently assorting C gene exert an epistatic effect on the brown nose phenotype, what phenotypic ratios would you expect if you bred reindeer that were double heterozygotes for the B and C genes, and why would you see such ratios? (6 points)


12. Describe two common mechanisms for the genesis of spontaneous mutations in DNA. (4 points)


13. In the DNA polymerase I gene, codon number 144 on the sense strand (equivalent to the mRNA) in the wild type sequence is normally TGG, which encodes a crucial amino acid in the enzyme. Show single nucleotide substitution mutations in the DNA that would convert this wild type codon to: (6 points)
a) a silent mutation

b) a nonsense mutation

c) a missense mutation


13. In horses a test cross is done between a doubly homozygous recessive line and a line of animals that are heterozygous for the same two genes A and B, which affect coat color and tail length. You end up with a large pasture full of progeny colts with the following distribution of phenotypes.
A B 122
A b 100
a B 91
a a 79
Are the genes assorting independently? Test this hypothesis with a statistical test. When you have done the test and drawn your conclusion about independent assortment, inspect the ratios again. Do you see anything odd, and if so, can you think of an explanation for it? (10 points)