Genetics Exam 1

In fruit flies, black body type is a recessive variant of the wild-type brown body. You cross two true-breeding black-bodied flies, and the resulting offspring all have brown bodies. Which of the following best explains this result? the black body mutations are codominant the black body mutation is dominant to the wild type each black fly had a mutation in a different gene the two black flies had mutations in the same gene

each black fly had a mutation in a different gene the two black flies had mutations in the same gene

Part II: What is the probability the child will have polydactyly but not DMD? Enter your answer to two decimal places (e.g., 0.88).

.38

Part III: What is the probability that the child will have either DMD orpolydactyly, but not both? Enter your answer to two decimal places (e.g., 0.88).

.5

What genotypic ratio do you get from a heterozygote cross (Tt x Tt)? 1 Tt : 1 tt 1 TT : 1 tt 1 TT : 1 Tt : 1 tt 1 TT : 2 Tt : 1 tt

1 TT : 2 Tt : 1 tt

In the Dorset sheep breed, both males and females have horns, and the trait is controlled by an autosomal gene. When true‑breeding Dorset sheep (HH) are crossed with true-breeding hornless type of sheep (hh), all the F1 males have horns and the F1 females are hornless. If two of these F1 sheep were intercrossed, what ratio of horned to hornless female sheep to you expect in the F2 generation? All horned 3 horned : 1 hornless All hornless 1 horned : 3 hornless

1 horned : 3 hornless

2. What phenotypic ratio do you expect in the F2 generation if tail length is controlled by a sex-linked gene, and long tails are dominant to short tails? Assume a chromosomal sex determination system as in mammals, with XX females and XY males. 1 long: 1 short 3 long: 1 short males 1 long: 1 short, females all short 1 long: 3 short

1 long: 1 short

Given a pair of 6-sided dice, what is the probability of rolling a total of 3? 1/6 1/3 1/18 1/36 1/72

1/18 For this question, you'll have to: Figure out the number of ways that two die can add up to 3 For each combination, use the multiplication rule to calculate the probability of getting that combination Remember that you only get to role the dice once, so the multiple different options are mutually exclusive of each other, and apply the addition rule.

Given a pair of 6-sided dice, what is the probability of rolling "double 6s"? 1/6 1/2 1/12 1/36 1/4

1/36

2. What is the probability of the child having cystic fibrosis? 1/4 3/4 3/16 3/8

1/4

A gecko has 2n=12 chromosomes. How many chromosomes does it have in a single cell at prophase of mitosis? 3 24 6 12

12

Part II: What are your degrees of freedom? Your answer should be a round number (e.g., 9).

2

A gecko has 2n=12 chromosomes. How many chromatids does it have in a single cell at prophase of mitosis? 12 3 6 24

24

Cotton is tetraploid (4n=52). After a cotton plant goes through meiosis, how many chromosomes does the pollen grain have? 52 13 26 104

26

What is the correct ploidy and chromosome number? X. X X. X X. X

2n=6

The next two questions go together. Suppose the tail length of two populations of lizards is controlled by one gene. To determine the mode of inheritance, a true-breeding short‑tailed female is crossed with a true-breeding long‑tailed male. Then, siblings from the F1 are crossed and the number of short‑ and long‑tailed animals are counted to determine the phenotype ratio. 1. What phenotypic ratio do you expect in the F2 generation if tail length is controlled by an autosomal gene, and long tails are dominant to short tails? males 1 long: 1 short, females all short 1 long: 1 short 3 long: 1 short 1 long: 3 short

3 long: 1 short

4. What is the probability of the child having cystic fibrosis but NOT albinism? 7/16 1/4 3/8 1/8 3/16

3/16

In a cross of AABbCCddEe x AaBbCcDdEe, assume that capital letters are dominant. What proportion of the offspring will show the dominant phenotype for A, B, and C and the recessive phenotype for D and E? 3/8 9/64 9/32 3/32 3/64

3/32

3. What is the probability of the child NOT having albinism? 1/4 3/4 9/16 1/2

3/4

Part III: Assuming a p-value cut-off of 0.05, what is the critical value that you will use to evaluate your hypothesis? 3.841 5.991 9.488 7.815

5.991

A gecko has 2n=12 chromosomes. How many homologous pairs does it have in a single cell at prophase of mitosis? 24 3 12 6

6

The next four problems are part of a series. For these problems, see your book for a detailed explanation of epistasis in labs, and also for the χ2 table. You have crossed two black labs that are both BbEe genotypes, and the resulting litter consists of 15 black, 4 brown, and 6 yellow labs. You conduct a χ2 test of the null hypothesis that the offspring match the expected ratios for recessive epistasis, and any differences are due to chance. The χ2 value you calculate is 0.190. Part I: How many yellow labs do you expect? Answer to one decimal place (e.g., 0.8).

6.3

5. What is the chance the child will have at least one condition? 3/16 7/16 10/16 1/16

7/16 Remember, there are three possible genotypes that we are interested in, but only one child, so the genotypes are mutually exclusive. We walked through the probability of getting one of the possible genotypes in the previous problems, but now you need to calculate the probabilities of the other possible genotypes and then apply the addition rule.

Miniature wings are recessive to normal size (wild-type) wings in fruit flies. You have two true-breeding lines of miniature wing flies from two different locations, and when you cross them all the F1 offspring have normal wings. When you intercross the F1offspring you get 200 F2 How many of these do you expect to have miniature wings? Enter your answer to one decimal point (e.g., 1.8).

87.5

A scientist in the rainforest finds 2 kinds of frogs: plain green (wild-type, dominant), and purple-spotted (mutant, recessive). She mates two true-breeding purple-spotted frogs, and the F1 offspring are plain green. If the F1s intercrossed, the F2 ratios would be: _____green : ________purple-spotted

9-7

An AaBb individual is crossed with an AaBb individual, and the ratio of phenotypes is calculated for the offspring of the cross. Assume that there is no interaction between the genes, and match the genotypes on the left with the appropriate phenotypic ratios on the right. A_B_ aaB_ A_bb aabb

A_B_ 9/16 aaB_ 3/16 A_bb 3/16 aabb 1/16

Cystic fibrosis is a disease expressed in homozygous recessive genotypes (ff). Albinism is also only expressed in the homozygous recessive form (aa). If two parents who are carriers for both cystic fibrosis and albinism have a child, what are the chances that it will have at least one of the conditions? 1. What is/are the target genotypes? A_ff A_ff, aaF_, or aaff aaff aaF_ A_ff or aaF_

A_ff, aaF_, or aaff

You are trying to determine whether a horn shape (curved = dominant, straight = recessive) in cows is controlled by a sex-linked or autosomal gene. You cross a true-breeding curved female with a true-breeding straight male and all the F1offspring have curved horns. What outcome would you expect in the F1 if the trait was controlled by a sex-linked gene and you conducted a reciprocal cross? All straight All curved All curved females: all straight males All straight females: all curved males

All curved females: all straight males

What would you get if you crossed a true-breeding peach with a true-breeding orange pepper? All cream All red 9 red : 3 peach : 3 orange : 1 cream 3 red : 1 cream

All red

The next two questions are part of a set: 1. Black beak color is a recessive, sex-linked trait in chickens. What offspring do you expect if you cross a true-breeding black-beaked female chicken with a true-breeding yellow-beaked male? All yellow All black females: All yellow males All black All yellow females: All black males

All yellow Remember that chickens are birds! The XY sex chromosome system doesn't apply here.

A dog breeder has a true-breeding line of yellow labs. What are the possible genotypes of the labs in this population? bbEE Bbee bbee BBee

Bbee bbee BBee

Coat color in cats is controlled by multiple alleles at a single locus, with ordered dominance as follows: b+ > bb > bc, where b+ causes black fur, bb causes brown fur, and bc causes cinnamon fur. If you cross a b+bc cat with a bbbc cat, what phenotypes do you expect to see in the offspring, and in what proportion? Enter your answers to two decimal places (e.g., 0.88), not as fractions or descriptions. Black? Cinnamon? Chocolate?

Black 1/2 chocolate 1/4 cinnamon 1/4

What is the correct notation for a colorblind male? Choice 1: XcY Choice 2: XcXcY Choice 3: X+Y Choice 4: X+XcY

Choice 1

What is the correct notation for a colorblind male who is also a carrier for albinism (autosomal)? Choice 1: XcAaY Choice 2: AaXcY Choice 3: XcYXAXa Choice 4: XcYXAYa

Choice 2

Genomic imprinting, where gene expression is based on the sex of the transmitting parent, demonstrates which of the following? Epistasis Sex-linkage Epigenetics Pleiotropy

Epigenetics

Part IV: Do you reject or fail to reject the null hypothesis? Why? Reject, because the p-value is less than 0.05 Fail to reject, because the p-value is less than 0.05 Reject, because the p-value is greater than 0.05 Fail to reject, because the p-value is greater than 0.05

Fail to reject, because the p-value is greater than 0.05

After learning about the atrocities committed by the Nazi party, the US outlawed forced sterilizations starting in 1945. True False

False

Recessive alleles are never transcribed in heterozygous individuals. True False

False

True or false: homologous chromosomes are the result of DNA replication. True False

False

Which of the following can we currently detect using pre-implantation genetic testing? Personality traits Genetic diseases controlled by a single gene Sex Political beliefs

Genetic diseases controlled by a single gene Sex

______________________________ sex determination is based on the inheritance of alleles at one or more loci, in the absence of differentiated sex chromosomes.

Genic

A scientist in the rainforest finds 2 kinds of frogs: plain green (wild-type, dominant), and purple-spotted (mutant, recessive). She mates two true-breeding purple-spotted frogs, and the F1 offspring are plain green. The F1 genotypes must be: GgPp GGpp ggPP Gg

GgPp

Based on the genetics of sex determination in butterflies*, you expect males and females to occur in a ratio of 2:1. During your field survey this year, you count 42 male and 18 female butterflies. Which of the following represents an appropriate, testable null hypothesis for this data? *Note: this is not how sex determination in butterflies actually works! It's just an example. There are 40 male and 20 females. There are 42 male and 18 female butterflies, any differences are due to chance. Males and females occur in a 2:1 ratio, and differences are due to chance. There will be an equal number of male and female butterflies, any differences are due to chance.

Males and females occur in a 2:1 ratio, and differences are due to chance.

Coat color in cats is determined by genes at several different loci. At one locus on the X chromosome, one allele (X+) encodes black fur and another allele (XO) encodes orange fur. Females can be black (X+X+), orange (XOXO), or a mixture of orange and black called tortoiseshell (X+XO). Males are either black (X+Y) or orange (XOY). Bill has a female tortoiseshell cat named Patches. One night, Patches escapes from Bill's house, spends the night out, and mates with a stray male. Patches later gives birth to the following kittens: one orange male, one black male, two tortoiseshell females, and one orange female. What are the genotypes of Patches, the stray male, and the kittens? (Note: Superscripts are not possible in the answers, so consider Xo to be equivalent to XO and X+ to be equivalent to X+.)

Patches X+Xo Stray male XoY Orange male kitten XoY Black male kitten X+Y Orange female kitten XoXo

A gene that controls more than one trait is ___________________________________. (Be sure to check your spelling on this one.)

Pleiotropy

When an Rr individual makes gametes, you expect that 50% will be R and 50% will be r. Which of Mendel's principles predicts this equal production of gamete types? Principle of Dominance and Recessivity Principle of Independent Assortment Principle of Segregation

Principle of Segregation

If we say that a round-seed pea plant is a carrier for the wrinkled trait, what is its genotype? RR rr Rr

Rr

Match the descriptions of different modes of sex determination on the left with the mechanisms on the right. Sex is determined by temperature. One sex has half the chromosome number of the other sex. Sex is controlled by a locus or loci, which can be in the cytoplasm. Individuals can change sex during their lifetime. One chromosome will lose genes over time.

Sex is determined by temperature. Environmental sex determination One sex has half the chromosome number of the other sex. Chromosomal sex determination Sex is controlled by a locus or loci, which can be in the cytoplasm. Genic sex determination Individuals can change sex during their lifetime. Environmental sex determination One chromosome will lose genes over time. Chromosomal sex determination

Snapdragons occur in nature as either green‑ or yellow‑leaved plants. Suppose that a gardener crosses two yellow‑leaved snapdragons, and one‑third of the offspring have green leaves while two‑thirds of the offspring have yellow leaves. What is the most likely explanation for this outcome? The allele causing yellow leaves is a recessive epistatic allele The allele causing yellow leaves is carried in the chloroplast genome The allele causing yellow leaves is a recessive lethal allele The allele causing yellow leaves is a dominant lethal allele

The allele causing yellow leaves is a recessive lethal allele The allele causing yellow leaves is a dominant lethal allele

The US eugenics movement rose to prominence in the 1920s, but its origins are in the 1900s. What event occurred in 1900 that corresponded with this early origin? The Immigration Restriction Act of 1924. The Supreme Court Buck v. Bell decision. The rediscovery of Mendel's work.

The rediscovery of Mendel's work.

If the number of individuals you expect and the number of individuals you observe are identical to each other, which of the following statements will be true? Note that you can select multiple answers. The χ2 value will be large. The χ2 value will be small. The p-value will be small. The p-value will be large.

The χ2 value will be small. The p-value will be large.

A scientist in the rainforest finds 2 kinds of frogs: plain green (wild-type, dominant), and purple-spotted (mutant, recessive). She mates two true-breeding purple-spotted frogs, and the F1 offspring are plain green. This indicates that: There are mutations at two different genes causing purple spots (complementation). No answer text provided. There is a single gene controlling color, and the purple-spotted mutations are allelic (failure to complement). Impossible - you cannot cross two recessives and get a dominant phenotype.

There are mutations at two different genes causing purple spots (complementation).

The genetic notation indicating the composition of the human genome is 2n=46. What does the "2" indicate? There are two copies of each chromosome type. There are two cells produced by mitosis. There are two telomeres on an unreplicated chromosome. Replicated chromosomes consist of two chromatids.

There are two copies of each chromosome type. Correct! In genetic notation, the number before the "n" indicates the number of each chromosome type present in the genome. In this course, we'll often deal with diploids (2n), but haploids (n), triploids (3n), and higher ploidy levels will also show up.

Match each of the definitions and examples to the form of dominance or epistasis exhibited. Choices can be used more than once, and every choice will be used at least once. Two alleles of one gene are responsible for eggplant color, and eggplants can be purple and white Alleles at one gene mask the effect of another gene The heterozygous phenotype has both homozygous phenotypes equally expressed One allele masks the effect of another allele Two alleles of one gene are responsible for eggplant color, and eggplants can be purple, lavender, and white Alleles at two genes interact to influence the same phenotype, but no allele masks the other

Two alleles of one gene are responsible for eggplant color, and eggplants can be purple and white Dominance Alleles at one gene mask the effect of another gene Epistasis The heterozygous phenotype has both homozygous phenotypes equally expressed Codominance One allele masks the effect of another allele Dominance Two alleles of one gene are responsible for eggplant color, and eggplants can be purple, lavender, and white Incomplete Dominance Alleles at two genes interact to influence the same phenotype, but no allele masks the other Additivity

In the Buck v. Bell decision, Supreme Court Justice Oliver Wendell Holmes, Jr., compared forced sterilization to what widely used medical practice? Antibiotics Post-natal genetic testing Vaccination

Vaccination

All of the cats who reside at the Ernest Hemingway Museum in Key West, Florida, carry at least one dominant allele for polydactyly. However, only about half the cats display an extra toe on their paws; the others have the expected number of toes. Which of the following is a possible explanation for this? Variable penetrance Variable expressivity Incomplete dominance Cytoplasmic inheritance

Variable penetrance

Cytoplasmic inheritance occurs when genetic information is transmitted by means other than through nuclear DNA. Select the examples of mitochondrial or chloroplast inheritance from the choices below. White leaves in Mirabilis jalapa are caused by a mutation that affects chlorophyll production. Some watermelons produce seedless fruits because the plants are triploid Narrow, slit-like eyes in Drosophila are produced as the result of a duplicated X chromosome region Slow growth in Neospora occurs because of a mutation that inhibits the electron transport chain

White leaves in Mirabilis jalapa are caused by a mutation that affects chlorophyll production. Slow growth in Neospora occurs because of a mutation that inhibits the electron transport chain

In sheep, the allele for black fleece (w) is recessive to white (W). You cross a white sheep with a true-breeding black sheep and there is one black and one white lamb as a result. What is the genotype of the white sheep? WW Ww W_ ww

Ww

What is the sexual phenotype of an XXY individual with the SRY gene deleted? Female Male

XXY

Which type of aneuploidy shows the relatively minor contribution of the Y chromosome to human development? X0 XXX XXY XYY

XYY

Which of the following will tend to lose genes over evolutionary time due to sex chromosome degeneration? X chromosome in mammals Y chromosome in mammals Z chromosome in birds W chromosome in birds

Y chromosome in mammals W chromosome in birds

The next three questions go together. Duchenne's muscular dystrophy (DMD) is a disease caused by a recessive allele at a gene on the X chromosome. Polydactyly is caused by a dominant allele at an autosomal gene. If a phenotypically normal woman who's father had DMD has a child with man who is heterozygous for the allele causing polydactyly but is otherwise normal, what is the probability that the child will have either DMD orpolydactyly, but not both? Part I: What is the cross? A = ppXDXd x PpXDXD B = PPXDXd x PpXDY C = ppXdXd x PpXdY D = ppXDXd x PpXDY

d

An AaBb individual is crossed with an AaBb individual, and the ratio of phenotypes is calculated for the offspring of the cross. In this case, there is an epistatic interaction between the genes and the ratio of offspring is 9:6:1. What genotypes below make up the phenotypic of 6 in this ratio? aaB_ aabb A_B_ A_bb

aaB_ A_bb

For this cell, the different types of lines (straight, wavy, dotted) represent different non-homologous chromosomes. What is n? X X X. X X. X n=6 n=2 n=4 n=3

n=3

In pea plants, tall height is dominant (T) and short height (dwarfing) is recessive (t). If a plant is true-breeding for short height, what is its genotype at the locus controlling height? TT Tt tt

tt