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Practice Exam and Quizzes

EXAM I PRACTICE QUESTIONS

BSCI 222 (Genetics).

NAME________________________________

ID: ____________________________________

1. Total = 15 pts. Define 5 of the following 8 terms (3 pts each = 15 pts):

Sister chromatid, diploid, phenotype, codominance, homologous chromosome, allele, homozygous, chromosomal interference

2. Total = 5 pts. How many different gamete genotypes would a AaBBCCDdEeFFggHhIi individual make for the loci described? Show work.

3. Total = 4 pts. A cross between 2 pea plants gave rise to an F1 that all had green stems. The F1’s were allowed to self-fertilize, giving rise to an F2 consisting of 123 green-stemmed and 41 purple-stemmed plants. Provide a hypothesis for the genotype and phenotype of the 2 parents (2 pts). What phenomenon does the F1 manifest (2 pt)?

4. Total 8 pts. Drosophila melanogaster has 8 chromosomes in its somatic cells.

a. How many chromosomes does a D. melanogaster zygote receive from its male parent? 2pts

b. How many autosomes and how many sex chromosomes are present in each somatic

cell? 2 pts

c. How many chromosomes are present in a D. melanogaster egg? 2 pts

d. How many sex chromosomes are present in a D. melanogaster egg? 2 pts

5. Total = 9 pts. Simo simpleton, is a very simple organism with haploid chromosome number, n=2. Imagine you have a powerful microscope and can view the chromosomes during Metaphase I of Meiosis. Draw what you see.

A. Clearly label the homologous chromosomes, centromere, sister chromatids, non homologous chromosomes, nonsister chromatids. (5 pts)

B. For a double heterozygote individual for two unlinked loci, A, B, (so individual is AaBb) the gametes following meiosis are AB and ab. Place the appropriate alleles on the chromosomes in the correct orientation during Metaphase I of Meiosis (2pts). Another time you see that the gametes are Ab and aB. Place the appropriate alleles on the chromosomes in the correct orientation during Metaphase I of Meiosis (2pts).

6. Total = 14 pts. In the ABO blood classification, occasionally people with the A and/or B alleles appear to have type O blood. This occurs when the person is homozygous recessive at another unlinked locus (call it locus H, with the recessive homozygote denoted hh). This second unlinked locus encodes a substance necessary for the expression of A, B, and AB blood types. This substance is a protein that allows the sugars associated with the A, B, or AB blood types to be attached to the red blood cells.

A. What is the genetic phenomenon called where the blood type phenotype of an individual depends on the genotype at the second H locus? (3 pts)

B. If two ABHh individuals were to mate, what are the possible genotypes of the offspring and what are their expected frequencies? (3 pts)

C. What are the phenotypes (A, B, AB or O) that are expressed and in what frequencies are they expressed? (8 pts)

7. Total = 12 pts. Suppose a three-point testcross was conducted involving the linked genes A, B and C, using 1000 progeny. If the most abundant gamete classes are ABc and abC and the rarest classes are Abc and aBC, which gene is in the middle? (4 points).

b. B

Cannot be determined

For the same cross, the frequencies of gamete classes are:

AbC 5%

aBc 5%

ABC 5%

abc 5%

but the frequency of Abc plus the frequency of aBC gametes is 0.5% (1/2 of 1%).

What phenomenon does the presence of Abc and aBC gamete types demonstrate (2pts)? Calculate the coefficient of coincidence across the region of chromosome spanning the loci ABC (3 pts) and provide the value of interference (3 pts).

8. Total = 15 pts. Female Drosophila melanogaster are test-crossed to homozygous recessive males. From the below data of 1000 progeny, give the genotype(s) of the parents of the females used in the cross (2 pts) estimate the frequency of recombination between cn and vg, cn and y and vg and y (9 pts) and linkage arrangements of the 3 loci (4 pts). All females have the same parents and the parents are true breeding.

cn vg y / cn vg y 227

+ + + / cn vg y 233

cn vg + / cn vg y 228

+ + y/ cn vg y 232

cn + +/ cn vg y 17

+ vg y/ cn vg y 22

cn + y/ cn vg y 18

+ vg +/ cn vg y 23

10. Total 3 pts. The union of a sperm and an egg is the union of _____________.

A. two gametes to form a zygote

B. two diploids cells to form a haploid cell

C. two zygotes to form a gamete

D. two haploid cells to form a diploid cell

E. both a and d

F. both c and b

G. both c and d

11. Total = 5 pts. The goal of genetics is determine the genetic basis of phenotypic differences. Which of the following phenomenon contribute to genetic variation and hence phenotypic variation in populations. CIRCLE YOUR ANSWER(S).

A. Mitosis

B. Meiosis I

C. Meiosis II

D. Independent Assortment

E. Recombination

I. True /False. If the statement is false, write the changes required to make it correct (2 points each).

1. ( ) The process of meiosis results in four identical diploid cells.

3. ( ) Recombination is the exchange of genetic material that occurs between sister chromatids during prophase II.

1. ( ) Complementary gene action occurs when two alleles of the same gene are necessary to produce a particular phenotype.

2. ( ) Epistasis refers to the gene interaction in which an allele at one gene masks the effects of alleles at a different gene.

1. ( ) Recombination is uniform over the length of a chromosome.

2. ( ) The preponderance of parental genotypes in the F2 generation is an indication of linkage

II. Problems

BSCI 222 Quiz # 1

Name________________________________________

TA ___________________________________________ Section _______________________

1. Provide definitions for the following terms (1 pt. each) :

A. Recombination: __________________________________________________________________

__________________________________________________________________________________

B. Centromere:____________________________________________________________________________________________________________________________________________________

2. If an individual has genotype Aa, draw all possible arrangements of the chromosomes and chromatids, containing the “A” locus at Metaphase I of Meiosis. What are the genotypes of the gametes produced?

3. Do the same for an individual that is AaBb where the “A” and “B” loci are on different chromosomes. What are the genotypes of the gametes produced? Indicate metaphase plate, homologous chromosomes and sister chromatids.

Gametes: __________________________ _____________________________

BSCI 222 Quiz # 2

Name________________________________________ Section _______________________

Part I. Match letters with the correct definitions (0.5 pts each)

A. Law of Segregation

B. Codominance

C. Law of Independent assortment

D. Testcross

E. Phenotype

F. Complementation test

G. Pleiotropy

H. Locus

I. Incomplete dominance

J. Recessive lethal allele

( ) During gamete formation different pairs of alleles segregate independently of each other

( ) One gene determines two unrelated traits

( ) An allele that causes the death of homozygotes, although it can be carried in the heterozygotes.

( ) A cross between a homozygote dominant and a homozygote recessive produces an individual with an intermediate phenotype.

( ) Observable characteristic

( ) The two alleles for each trait separate during gamete formation and then unite at random at fertilization.

( ) A designated location in a chromosome.

( ) The traits determined by each allele of a pair are both visible in the heterozygotes

( ) Cross to determine the genotype of an individual with a dominant phenotype by mating it with an individual showing the recessive phenotype.

( ) Method to determine if a particular phenotype arises from mutations in the same or in different genes.

2. Albinism in humans is caused by a recessive allele. Two normal parents have an albino child and they are expecting a second baby. Use “A” and “a” to designate the normal and recessive alleles respectively.

a) What are the genotypes of the parents? 2 pts

b) What is the probability that their second child is a boy and albino ? 1pt.

c) The parents finds out they are going to have non-identical twins. What is the probablility that both twins will be girls and albino? 2pt.

BSCI 222 Quiz # 3

Name________________________________________ Section _______________________

Part I. True /False. If the statement is false, write the changes required to make it correct (2 points each).

1. ( ) Pleiotropy is the phenomenon in which a more than one gene determines a set of unrelated traits.

2. ( ) Epistasis refers to the gene interaction in which an allele at one gene masks the effects of alleles at a different gene.

3. ( ) The proportion of individuals with a particular genotype expressing the expected phenotype is known as expressivity .

4. ( ) In systems with incomplete dominance heterozygotes resemble one of the parents.

Part II. Short answer (12 points)

1) You cross two true breeding lines of an African Violet, one variety has white flowers and the other one has yellow flowers. The F1 plants are all white but when you allow the F1 plants to self-fertilize, you obtain 123 white-flowered plants, 31 red-flowered plants and 11 yellow- flowered plants. Describe the most likely form of inheritance of flower color? What are the genotypes of the two parental strains, the F1 and the F2 offspring (for the F2 use underscores if there is more than one possible genotype?

P White X Yellow

Genotypes: ___________ X __________

F1 White

Genotype: ____________

Self-fertilization

F2 123 White, 31 Red, 11 Yellow

Genotypes: ____________, _____________, _____________

BSCI 222 Quiz # 4

Name_________________________________ Section _______________________

Part I. True /False. If the statement is false, write the changes required to make it correct (2 points each).

1. ( ) Recombination occurs exclusively by crossing over between non-sister chromatids of homologous chromosomes.

2. ( ) Linkage occurs when alleles of two or more genes travel together on the same chromosome.

3. ( ) In a three point cross the gene that lies in the middle is identified by the offspring classes with the largest number of offspring.

Part II. Problems (14 points)

In some black flies, gene “S” determines the production of spines on the legs, while another allele produces non- spiny legs. A second gene “W” which lies on the same chromosome, determines the production of wings, while the mutation w produces wingless individuals. A cross between true breeding spiny, winged flies and non-spiny, wingless flies resulted in F1 individuals that were winged and had spiny legs. When these F1 individuals were crossed to a homozygous recessive individual, the offspring was composed of 403 spiny/ winged, 397 non-spiny/ wingless, 102 spiny/wingless and 98 non-spiny/ winged flies.

1. What are the dominant alleles for each gene and which phenotypes do they represent?

2. What gametes are produced by F1 individuals. Indicate which are parental and which are recombinant.

3. Calculate the distance between “S” and “W”?

4. A black fly whose parents were true breeding “non-spiny, winged” (mom) and “spiny, wingless” (dad), is test crossed to individual Y.

(a). What is the genotype of individual Y?

b) what phenotypic classes and in what proportions would you expect in the offspring from this test cross? (Tip: use information obtained in question 3).

Name: QUIZ #1 BSCI 222 Genetics

TA: Kevin Barry

~~1)How many sub-stages does Prophase I have?(2)~~

2)Define chiasma(2)

3) A diploid organism has 2 chromosomes in each somatic cell. How many daughter cells will be produced by mitosis, and how many chromosomes will each have? If one of the cells undergoes meiosis, how many how many daughter cells will be produced, and how many chromosomes will each have?(4)

4) What is the name for a pair of homologous chromosomes?(2 pt)

5) If an individual has genotype Aa, draw all possible arrangements of the chromosomes and the chromatids, containing the “A” locus at Metaphase I of meiosis. What are the genotypes of the gametes produced? Do the same for an individual that is AaBb where the “A” and “B” loci are on different chromosomes. What are the genotypes of the gametes produced? (10 pts)

1. What phenotypic ratio does one get from a cross of two individuals both heterozygous for a single trait (a monohybrid cross)? (2 pts.) What would the genotypic ratio be? (2 pts)

2. Which form of dominance would cause a monohybrid cross to result in a 1:2:1 phenotypic ratio? (more than one can be selected)(4 pts)

a. complete dominance

b. incomplete dominance

c. codominance

3. Define pleiotropy (3 pts)

4. Define allele (3 pts)

5. If yellow(Y) color is dominant to brown (y) color, and straight(S) hair is dominant to curly(s) hair, what will the phenotypic ratio be for the offspring in a dihybrid cross (YySs x YySs)?. Show the punnet square (8 pts)

1.What is the probability that a father with a Y-linked disease will pass this disease to his daughter?(3 pts)

A. 1/4

B. 3/4

C. 0/4

2. Define TWO of the following (2.5 pts each)

Pleiotropy, epistasis, penetrance, expressivity

4. You cross two true breeding lines of an Sfrican violet, one variety has white flowers and the other one has yellow flowers. The F1 plants are all white, but when you allow the plants to self fertilize, you obtain 123 white-flowered plants, 31 red-flowered plants, and 11 yellow-flowered plant. Describe the most likely form of inheritance of flower color (2 pts). What are the genotypes of the two parental strains, the F1, and the F2 offspring (If there is more than one possible genotype, but sure denote this)(10 pts)

1. There is linkage between genes when (3 pts):

a) PD = NPD

b) PD << NPD

c) PD >> NPD

d) T = PD

2. When looking at the gametes of an individual heterozygotic at two genes, you notice that 84% are the parental type. How far apart are these genes on the chromosome? (5 pts)

3. How many cells undergo meiosis to produce the 8-cells within an ascus? (4 pts)

a) 1

b) 2

c) 4

d) 8

4. Looking at the following chromosome segment from an ABC/abc individual, what percentage of gametes will result from a double-crossover? (8 pts)

60 cM 5 cM

|| ||

\/ \/

----A------------B-------C----

The centromere holds two homologous chromosomes together.

True

False

The end product of meiosis in a diploid animal:

A. determines the transmission of genes from parent to offspring

B. yields haploid cells containing two copies of all of the parent’s genes

C. yields diploid cells containing four copies of all of the parent’s genes

D. allows the parent to adapt to its environment

Indicate the appropriate stage of meiosis (meiosis I, meiosis II, meiosis I&II) for each event below:

Spindle apparatus forms. _______________

Homologous chromosome pairing occurs. _________________

Non-sister chromatids are found in the same cell. ________________

Centromere division occurs. _________________

Identical copies of a chromosome attached by a centromere are called:

A. twins

B. sister chromatids

C. non-sister chromatids

D. homologous chromosomes

(10 pts) If an individual has genotype Dd, draw all possible arrangements of the chromosomes and chromatids containing the “D” locus at metaphase I of meiosis. What are the genotypes of the gametes produced? Do the same for an individual that is DdEe where the “D” and “E” loci are on different chromosomes. What are the genotypes of the gametes produced?

Define Mendel’s Law of Segregation.

What is a testcross? Why does it work in all cases?

What is the difference between incomplete dominance and codominance?

Suppose that two genes (A and B) specify the production of two enzymes that are both necessary to produce red eyes in Drosophila. Being homozygous recessive for either gene will cause white eyes. What ratio of normal to white eye individuals will result from a cross between dihybrid parents (heterozygous for both genes)?

Under what conditions could a monohybrid cross give a 2:1 phenotypic ratio?

Choose the best phrase to describe each term (taken from the text)

epistasis ______	a. “the alleles of one gene mask the effects of alleles of another gene”
autosome ______	b. “a heritable change in a gene”
mutation ______	c. “structure formed at the spot where crossing-over occurs between homologs”
pleiotropy ______	d. “one crossover along a chromosome makes a second nearby crossover less likely”
interference ______	e. “chromosomes that do not differ between the sexes”
chiasma ______	f. “a single gene determining a number of distinct and seemingly unrelated characteristics”

In fruit flies there is an X-linked dominant mutant allele, designated N, that causes notched wings when heterozygous. However, N is a recessive lethal allele, causing the eggs to be inviable. What phenotypic ratio of offspring would be expected in a cross of notched winged females with wild-type (wt) males? (4 pts)

A. Males and females will both be 1:1 wt to notched

B. All males will be wt, and females will 1:1 wt to notched

C. All offspring will be notched females

D. Males will be 1:1 wt to notched, and all females will be notched

A woman who is heterozygous for X-linked colorblindness marries a man who does not carry the colorblind allele.

a. What portion of their sons would you expect to be color blind?

b. What portion of their daughters will be colorblind?

c. Which individuals in this question are hemizygous; the males, the females, or both?

A DdEe individual is crossed with a ddee individual. The F1 offspring were examined and the following genotypic classes were observed:

936 Dd Ee

864 dd ee

12 Dd ee

8 dd Ee

How far apart are genes “D” and “E”?

A three point cross was done examining genes causing white eyes (w), miniature wings (m), and a yellow body (y). The wild-type alleles of these genes are denoted w⁺, m⁺, and y⁺, and they are all X-linked so that males are hemizygous for these genes. A female heterozygous at all three genes is mated to a male. The male F1 offspring of this cross were examined and the following phenotypic classes were observed:

2278 w⁺ y⁺ m / Y 49 w⁺ y m / Y 1203 w y m / Y 2 w⁺ y m⁺ / Y

2157 w y m⁺ / Y 41 w y⁺ m⁺ / Y 1092 w⁺ y⁺ m⁺ / Y 1 w y⁺ m / Y

Indicate which phenotypic pair constitutes the parental class? (3 pts)

Indicate which pair constitutes the double crossover class? (3 pts)

Which gene is in the middle along the chromosome? (3 pts)

Which pair of genes is closest together on the chromosome? (3 pts)

What is the recombination frequency between m and w? (3 pts, if you don’t have a calculator you can just set up the equation)

If 2 genes in yeast are linked you would expect to see which of the following in the tetrads (select one of the following; 1 pt):

Parental ditypes outnumber nonparental ditypes.
The numbers of parental and nonparental ditypes to be equal.
Nonparental ditypes outnumber parental ditypes.

If 2 genes in yeast are unlinked you would expect to see which of the following in the tetrads (select one of the following; 1 pt):

a. Parental ditypes outnumber nonparental ditypes.

b. The numbers of parental and nonparental ditypes to be equal.

c. Nonparental ditypes outnumber parental ditypes.