Please read these carefully. One and only one response (a, b, c, d, or e) completely and correctly answers the question, or completes the statement. Circle the appropriate response and turn in this exam. Make sure your circle is unambiguous. Take time to relax. (Suggestion: put the problem into gene symbols, if that helps you to visualize the problem and its solution.)

1. Green colorblindness in humans is a sex-linked recessive trait. In a family, the older son has normal vision, whereas the younger son is colorblind. One can realistically surmise:
1. the mother was homozygous for colorblindness
2. the father was homozygous for colorblindness
3. the father was heterozygous for color blindness
4. the mother most probably was colorblind
5. none of the above
2. Coat color in dogs depends on the action of at least two genes. At one locus a dominant epistatic inhibitor of coat color pigment (I_) prevents the expression of color alleles at another independently assorting locus, thereby producing white coat color. When the recessive condition exists at the inhibitor locus (ii), the alleles of the second locus will be expressed, iiB_ producing black and iibb producing brown. When dihybrid white dogs are mated, what would be the phenotypic ratio in the offspring?
1. 12:3:1
2. 9:7
3. 9:3:3:1
4. 3:1
5. 1:2:1
3. What single information would most help in predicting genotypic frequencies of the progeny resulting from a cross?
1. the number of chromosomes
2. the allelic relationship, i.e. dominance, incomplete dominance, codominance
3. the frequency of the various possible parental phenotypes
4. the parental gametes
5. the parental phenotypes
4. A man learns that both his parents had Huntington's disease, which is caused by a dominant autosomal allele. What is the chance that he will have the disease?
1. 0%
2. 25%
3. 50%
4. 75%
5. 100%
5. Color of chickens is determined by interacting loci: AA or Aa give white, aaBB or aaBb give colored, and aabb produces white. What are the phenotypic frequencies of the offspring from a cross between two fully heterozygous chickens?
1. 15 white : 1 colored
2. 13 white : 3 colored
3. 12 white : 4 colored
4. 9 white : 7 colored
5. none of the above
6. Coat color of horses can be cremello (almost white), palomino (golden coat with lighter mane and tail), or chestnut (brown). Among these phenotypes, palomino never breed true. Cremello and chestnut always breed true when they are mated with other horses of the same coat color. What is the simplest explanation for these relationships?
1. multiple alleles
2. epistasis
3. codominance
4. inactivation of the X-chromosome
5. none of the above could explain the observations
7. Calico ("tortoise-shell") cats are always female because:
1. the maternal X chromosome is always heterochromatized into a Barr body
2. she always receives her X chromosomes from her mother, which may also be calico
3. either the maternal or paternal X chromosome is heterochromatized so all cells throughout the calico cat have the same inactivated chromosome
4. either the maternal or paternal X chromosome is randomly inactivated at an early stage of development
5. none of the above
8. The alleles determining human ABO blood types are an example of:
1. incomplete dominance
2. polygenes
3. sex linkage
4. all of the above
5. none of the above
9. Assume that a single gene has two alleles. In a diploid organism, how many possible genotypes are there?
1. 2
2. 3
3. 4
4. 6
5. 8
10. A maternity case involves an infant with type AB blood. Four women claim to be the mother. You be the judge, as far as the blood type evidence allows.
1. The woman with type A blood could not be the mother.
2. The woman with type AB blood could not be the mother.
3. The woman with type O blood could not be the mother.
4. The woman with type B blood could not be the mother.
5. All four women could be the mother
11. The plant of bread wheat has 42 chromosomes, thus:
1. during meiosis there will be 21 chromosomes going to each pole
2. during meiosis there will be 42 pairs of chromosomes
3. during mitosis there will be 21 chromosomes going to each pole
4. during mitosis there will be 14 chromosomes going to each pole
5. during mitosis there will be 7 chromosomes going to each pole
12. Heritability is a measure of the parent-offspring relationship in polygenic situations, and in situations where individual genetic effects cannot be measured. It is calculated as:
1. the variance divided by the mean
2. the sum of differences between observed and expected, divided by expected
3. the phenotypic variance divided by the environmental variance
4. the genotypic variance divided by the phenotypic variance
5. the phenotypic variance divided by the genotypic variance
13. Parent plants with the genotypes AABBCC and aabbcc were crossed, and their F₁ progeny were backcrossed to a homozygous recessive tester. The 1000 backcross progeny had the phenotypic distribution:

Phenotype ABC abc AbC aBc Abc aBC ABc abC

Number 190 190 40 40 160 160 110 110

What is the map distance between A and C?

1. 22 map units
2. 30 map units
3. 32 map units
4. 40 map units
5. 70 map units
14. Thalassemia is an inherited anemia controlled by a single allele. Homozygous persons have Thalassemia major, which is almost always fatal in childhood. Heterozygous persons have Thalassemia minor, and are mildly affected. An infant has Thalassemia major. What is the likelihood that a subsequent child of the same parents will have Thalassemia major?
1. 0%
2. 25%
3. 50%
4. 75%
5. 100%
15. In a genetics experiment on peas, far too few progeny were observed for a particular phenotypic class, compared with their expected frequency. This would fit with the statement that:
1. the null hypothesis should be rejected
2. the P value must be high, certainly P > 0.05
3. the experiment was a failure
4. all of the above
5. none of the above
16. Assume that a single gene has three alleles. In a diploid organism, how many possible genotypes are there?
1. 2
2. 3
3. 4
4. 6
5. 8
17. The haploid chromosome number of the horse is n=16. How many autosomes are there in the zygote?
1. 14
2. 15
3. 16
4. 30
5. 32
18. If the diploid chromosome number of an organism is n=16, the octoploid has:.
1. 8
2. 16
3. 24
4. 32
5. 64
19. One of the problems of autotetraploids in plants is that:
1. they cannot produce seed
2. their chromosomes do not pair and disjoin neatly
3. deleterious recessive alleles are exposed
4. all of the above
5. none of the above
20. Pattern baldness in humans is common in men because:
1. it is sex-linked
2. it is an example of cytoplasmic (extranuclear) inheritance
3. environmental effects
4. sex-influenced inheritance
5. none of the above

allele, continuous variation, dominance, epistasis, homologs, homozygosity, independent assortment, interphase, linkage, mitochondrion, mutation, nucleus, product law, trisomy, zygote

21. The __________________________________ holds that the probability of two independent events occurring simultaneously is found by multiplying their independent probabilities.
22. Down syndrome is the only human autosomal _________________________ in which a significant number of individuals survives longer than one year past birth.
23. During meiosis, homologous chromosomes are reshuffled in a random manner called
    
    ________________________________.
24. Prokaryotes don't have a true: ________________________________.
    
25. A form of a gene: ________________________________.
    
26. What results from polygenic inheritance __________________________________.

 

27. Recessive alleles are expressed only when they occur in a condition of
    
    __________________________________.
28. The type of chromosomes which are similar and can pair during meiosis
    
    _________________________________.
29. State of cell cycle when DNA replication occurs _______________________.
30. Masking of the effect of one gene by another _________________________________.
    
31. The postulate of Mendel that deals with relationship of alleles:
    
    __________________________________.
    
32. The diploid cell from the union of two haploid gametes. _______________________.
33. A condition giving rise to progeny ratios that would not be predicted on the Mendelian principle of independent assortment of genes during meiosis:
    
    _________________________________.
    
34. An organelle of eukaryotes which is involved with respiration
    
    __________________________________.
    
35. The characteristic of the genetic material associated with sudden genetic change:
    
    __________________________________.
    

39. Eye color in Drosophila is controlled by many genes, including the sex-linked White gene (recessive w is white) and the Sepia gene (recessive se is sepia, a brownish color; dominant Se is red). Only W_ genotypes express the Sepia gene and are thus sepia or brown. Draw the Punnett's square resulting from the cross of white females X sepia males and compile the expected frequencies of eye color among male and female offspring. (10 pts.)