Genetics Exam 1

Marfan syndrome is an autosomal dominant disorder caused by a mutation of the FBN1 gene that affects the connective tissue of the body. Suppose that two parents, a father with genotype fbn1 fbn1 and a mother with genotype FBN1 fbn1, are planning to have a family. What is the probability that they will have an affected daughter as their first child? Enter your answer as a decimal.

0.25

All of the following about sister chromatids is true except:

True: They will separate at anaphase of mitosis or anaphase of meiosis II. They have telomeres on each ends. They are attached at the centromere. False: Two chromatids attached at the centromere are considered a homologous pair.

Cell division by mitosis is a mechanism of asexual cell replication. Some single-cell organisms reproduce by cell division, and cell division enables multi-cellular organisms to grow and to repair damaged cells. Which of the following are products of cell division by mitosis?

Two daughter cells with identical chromosomes

Suppose two parents, a father with the genotype AaBbCcDdee and a mother with the genotype aaBbCCDdEe, wanted to have children. Assume each locus follows Mendelian inheritance patterns for dominance. What proportion of the offspring will have each of the following characteristics? Round your answers to two decimal places. * Same genotype as the father * Same phenotype as the father * Same genotype as the mother * Same phenotype as the mother

* 0.03 * 0.14 * 0.03 * 0.14

Polydactyly (PD) is an autosomal dominant trait (polydactyly = P; wildtype = p). Cystic fibrosis (CF) is an autosomal recessive trait (cystic fibrosis = f; wildtype = F). A PD woman, otherwise normal in phenotype, marries a healthy normal man. Their 4 children are: 1) normal, 2) PD, 3) CF, 4) CF PD. What is the probability that their 5th child will have AT LEAST ONE of these conditions? Answer to two decimal places. * What is the probability that the child will be PD? * What is the probability that the child will have CF? * What is the probability that the child with have both PD and CF? * What is the overall probability that the child will have at least one of these conditions?

* 0.50 * 0.25 * 0.13 * 0.63

An albino (autosomal, recessive) female human with normal vision and phenotypically normal parents has a non-albino brother who is colorblind (X-linked, recessive). She marries a phenotypically normal male human who knows he is a carrier for albinism. What is the probability their child will be phenotypically normal? (Give your answers to two decimal places.) * What is the probability that the female is a carrier for colorblindness? * If the female IS a carrier, and she and the male have a child together, what is the probability that it will be phenotypically normal? * If the female is NOT a carrier, and she and the male have a child together, what is the probability that it will be phenotypically normal? * What is the overall probability that the child will be phenotypically normal?

* 0.50 * 0.38 * 0.50 * 0.44

Phenylketonuria (PKU) is a disease that results from a recessive gene. Two normal parents produce a child with PKU. * What is the probability that a sperm from the father will contain the PKU allele? * What is the probability that an egg from the mother will contain the PKU allele? * What is the probability that their next child will have PKU? * What is the probability that their next child will be heterozygous for the PKU gene?

* 1/2 * 1/2 * 1/4 * 1/2

For this problem, see your book for a detailed explaination 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. * How many yellow labs do you expect? Answer to one decimal place. * What are your degress of freedom? * What is the corresponding critical value from the χ2 table? Answer to three decimal places. * Do you reject or fail to reject the null hypothesis?

* 6.3 * 2 * 5.991 * Fail to reject, because the χ2 value is less than the critical value.

In watermelons, bitter fruit (B) is dominant over sweet fruit (b), and yellow spots (S) are dominant over no spots (s). The genes for these two characteristics assort independently. A homozygous plant that has bitter fruit and yellow spots is crossed with a homozygous plant that has sweet fruit and no spots. The F1 are intercrossed to produce the F2. * What will be the phenotypic ratio in the F2? * If an F1 plant is backcrossed with the bitter, yellow-spotted parent, what phenotypes and proportions are expected in the offspring? * If an F1 plant is backcrossed with the sweet, nonspotted parent, what phenotypes and proportions are expected in the offspring?

* 9/16 bitter fruit, yellow spots; 3/16 bitter fruit, no spots; 3/16 sweet fruit, yellow spots; and 1/16 sweet fruit, no spots * All bitter fruit with yellow spots * 1/4 bitter fruit, yellow spots; 1/4 bitter fruit, no spots; 1/4 sweet fruit, yellow spots; and 1/4 sweet fruit, no spots

Suppose two independently assorting genes are involved in the pathway that determines fruit color in squash. These genes interact with each other to produce the squash colors seen in the grocery store. At the first locus, the W allele codes for a dominant white phenotype, whereas the w allele codes for a colored squash. At the second locus, the allele Y codes for a dominant yellow phenotype, and the allele y codes for a recessive green phenotype. The phenotypes from the first locus will always mask the phenotype produced by the second locus if the dominant allele (W) is present at the first locus. This masking pattern is known as dominant epistasis. A dihybrid squash, WwYy, is selfed, and produces 128 offspring. How many offspring are expected to have each of the following phenotypes? * White: * Yellow: * Green:

* White: 96 * Yellow: 24 * Green : 8

In cucumbers, dull fruit (D) is dominant over glossy fruit (d), orange fruit (R) is dominant over cream fruit (r), and bitter cotyledons (B) are dominant over nonbitter cotyledons (b). The three characters are encoded by genes located on different pairs of chromosomes. A plant homozygous for dull, orange fruit and bitter cotyledons is crossed with a plant that has glossy, cream fruit and nonbitter cotyledons. The F1 are intercrossed to produce the F2. What is the propability that one of the F2 offspring will have a dull, orange, and nonbitter phenotype OR a glossy, orange, and bitter phenotype? To answer, enter a decimal to two places

0.28

The allele Y in Drosophila is a dominant allele that is lethal when homozygous, but gives flies a yellow body color in the heterozygous condition with y, an allele for wild-type (brown) body color. At a second locus, the allele B for long bristles is incompletely dominant to the allele b for short bristles. Both loci are autosomal. If you cross two yellow body, medium bristled flies with each other, what is the probability that one of the living offspring will have the same phenotype as the parents? Answer to two decimal points.

0.33

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 are crossed with true-breeding hornless sheep, 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?

1 horned: 3 hornless

If an Aa individual is crossed to an aa individual, what will be the phenotypic ratio in the offspring?

1:1

Bread wheat (Triticum aestivum) is a hexaploid organism with 42 chromosomes (6n = 42). After meiosis is complete, how many chromosomes will be present in a single pollen grain?

21

Primula burmanica is 2n=44. How many homologous pairs are present at prophase of mitosis? Note that chromosomes do not have to be physically next to each other to be part of a homologous pair, they just need to be homologs in the same nucleus.

22 pairs

At the end of your biology class, your professor asks you to develop a project to determine the genotype of a plant with red flowers. Red petal color (R) is dominant to pink flower color (r). To accomplish this task, you cross the plant with the unknown genotype with heterozygous red-flowered plants. Which of the following are valid predictions of the ratio of flower colors in the offspring?

3 red: 1 pink OR All red

The annual sunflower (Helianthus annuus) has a diploid chromosome number of 2n=34. How many chromatids are there in a single cell at metaphase II of meiosis?

34

Suppose in a species of petunia, locus A determines petal color and locus B determines whether the petals can express any pigment. At locus A, purple petal color (A) is dominant over yellow petal color (a). At locus B, pigmentation (B) is dominant over lack of pigmentation (b). If an AA BB plant is crossed to an aa bb plant, what is the ratio of purple- to yellow- to white-flowered petunias expected in the F2 progeny?

9:3:4

X-linked red-green color blindness in humans is a recessive condition. Which of the following statements is true?

A color-blind woman must have had a color-blind father.

In humans, oculocutaneous (OCA) albinism is a collection of autosomal recessive disorders characterized by an absence of the pigment melanin in skin, hair, and eyes. That is, normal pigmentation (A) is dominant over albino characteristics (a). For this question, assume it is a single gene with two alleles. If both parents have normal pigmentation, what are all of the possible genotypes that may be observed in their offspring?

AA, Aa, or aa

Two unlinked genes control unicorn coat color. You cross a true-breeding purple unicorn with a true-breeding blue unicorn and all the F1 offspring are purple. Intercrossing these F1 individuals yields the following ratio of offspring: 9 purple: 3 teal: 3 red: 1 blue. What type of gene interaction does this represent?

Additivity

The white-eyed mutation in Drosophila studied by Thomas Hunt Morgan was the first clear case of sex-linked inheritance. When Morgan crossed a white-eyed female with a red-eyed male, what phenotypes were present in the offspring?

All of the males had white eyes and all of the females had red eyes.

In chickens the females are heterogametic, ZW, and the males are homogametic, ZZ. Most sex-linked genes are only carried on the Z chromosome. Congenital baldness is caused by a recessive sex-linked allele. If a bald male is crossed to a normal female, what would be the expected results in the offspring?

All the males will be normal and all the females will be bald.

Stages of Meiosis: Interphase

Chromosomes replicate

A man and a woman are both deaf, and deafness is a recessive, autosomal trait. However, when they have a child together, it has normal hearing. What could explain the fact that two deaf parents could have a child who is not deaf?

Complementation

Stages of Meiosis: Prophase I

Crossing over happens between homologous pairs

What process(es) unique to meiosis is/are responsible for genetic variation and at what point in meiosis do(es) each occur?

Crossing over of non-sister chromatids that takes place during prophase I. Random allignment and separation of homologs that takes place during metaphase I and anaphase I.

Describe shared characteristics between mitosis and meiosis

Duplication of chromosomes occurs before cell division

Describe Incomplete Dominance

EX: Two alleles of one gene are responsible for flower color, which can be red, pink, and white.

You are testing the null hypothesis that the outcome of a dihybrid cross conforms to a 1:1:1:1 ratio resulting from a cross between a heterozygous individual (AaBb) and a homozygous recessive individual (aabb), and that any differences are due to chance. Your calculated χ2 value is 5.721. Do you reject or fail to reject your null hypothesis? Assume a significance cut-off of P < 0.05

Fail to reject, because the χ2 value is less than the critical value.

Describes Y-linked traits?

Female offspring cannot inherit the trait. The phenotype is solely expressed in males.

Describe characteristics unique to meiosis

Forms sex cells such as egg and sperm. Contributes to genetic diversity such as crossing over.

Stages of Meiosis: Telophase I and Cytokinesis

Forms two cells

A gene whose expression is affected by epigenetic tags based on the sex of the transmitting parent demonstrates which of the following?

Genomic Imprinting

Stages of Meiosis: Metaphase I

Homologous pairs of chromosomes line up on the metaphase plate.

Stages of Meiosis: Anaphase I

Homologous pairs separate

What term describes an individual possessing two of the same alleles at a gene locus?

Homozygous

What information can the chi-square goodness-of-fit test provide?

How well the observed results of a genetic cross fit the expected values.

What is the physical appearance or manifestation of a characteristic called in genetics?

Phenotype

Pine trees have male and female cones on the same tree. Which term describes the sex system of the organism?

Monoecious

Describe Dominance

One allele masks the effect of another allele. EX: Two alleles of one gene are responsible for flower color, which can be red or white.

In mammals, why is aneuploidy of the X chromosome more often viable than aneuploidy of the autosomes?

Only one X chromosome remains fully functional in mammalian cells. Many or all genes on additional X chromosomes are silenced early during development.

In butterflies, sex is determined by the ZW sex-determination system. Female butterflies are heterogametic and have both a Z sex chromosome and a W sex chromosome for sex determination. In contrast, male butterflies are homogametic and have two Z sex chromosomes. Select all of the relatives from which a female butterfly could have inherited her Z sex chromosome.

Paternal grandfather and father

Which of the following statements accurately describes both pleiotropy and polygenic inheritance?

Polygenic inheritance refers to the cumulative effect of two or more genes on a single trait. Pleiotropy refers to a single gene that affects multiple traits.

An individual possesses two alleles at a locus and these two alleles separate when gametes are formed, one allele going into each gamete. This genetic concept is known as which of the following?

Principle of Segregation

Stages of Meiosis: Telophase II and Cytokinesis

Produce four cells.

You cross a round-seeded pea plant that is heterozygous for the allele controlling seed shape (Rr) with a true-breeding wrinkled pea plant (rr). There are 73 round and 127 wrinkled offspring. The null hypothesis is that the cross conforms to the expected ratio of an Rr x rr cross with one dominant (R) and one recessive (r) allele. Do you reject or fail to reject the null hypothesis? Assume a significance cut-off of p < 0.05

Reject

Characteristics unique to mitosis

Results in genetically identical cells. Used for asexual reproduction.

With the genic sex-determination mechanism, which of the following statements is true?

Sex is determined by genes on undifferentiated chromosomes

Color blindness is a sex-linked recessive trait. A female is color blind in one eye, but not both. Select the explanation for this condition.

Silencing of different X chromosomes

Stages of Meiosis: Metaphase II

Sister chromatids line up on the metaphase plate.

Stages of Meiosis: Anaphase II

Sister chromatids separate

Extranuclear inheritance, including mitochondrial and chloroplast inheritance, occurs in eukaryotes when genetic information is transmitted by means other than through nuclear DNA. Select the examples of mitochondrial or chloroplast inheritance.

Small-sized colonies of Saccharomyces cerevisiae are produced because of a mutation that produces abnormal electron transport. White leaves in Mirabilis jalapa are caused by a mutation that affects chlorophyll production.

Stages of Meiosis: Prophase II

Spindle fibers reform

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 explaination for this outcome?

The allele causing yellow leaves is a recessive lethal allele.

Describe Epistasis

The allele of one gene masks the effect of another gene.

Achondroplasia is a common cause of dwarfism in humans. All individuals with achondroplasia are thought to be heterozygous at the locus that controls this trait. When two individuals with achondroplasia mate, the offspring occur in a ratio of 2 achondroplasia:1 normal. What is the most likely explanation for these observations?

The allele that causes achondroplasia is a recessive lethal allele.

A yellow female Labrador retriever was mated with a brown male. Half of the puppies were brown, and half were yellow. Explain how the same female, when mated with a different brown male, could produce only brown offspring.

The first male was bb Ee, and the second male was bb EE.

Describe Codominance

The heterozygous phenotype has both homozygous phenotypes equally expressed. EX: Two alleles of one gene are responsible for flower color, which can be red and white petals, red and white.

Genomic imprinting occurs when gene expression in the offspring depends upon whether a particular allele was inherited from the mother or the father. Which of the following statements is likely to explain the evolutionary basis for the existence of imprinting?

The ideal reproductive strategy is different for males and females. For example, maximum birth weight and fetal growth are favored by fathers because they increase offspring survival. Mothers favor maternal survival and the preservation of resources for future reproduction. Therefore, a mother may benefit from reduced fetal growth rates.

A homozygous variety of opium poppy (Papaver somniferum Laciniatum) with lacerate leaves was crossed with another homozygous variety with normal leaves. All the F1 had lacerate leaves (jagged-edged leaves). Two F1 plants were crossed to produce the F2. Of the F2, 249 had lacerate leaves and 16 had normal leaves. How are lacerate leaves determined in the opium poppy? Give genotypes for all the plants in the P, F1, and F2 generations. Some generations will have more than one genotype. * P * F1 * F2 (lacerate) * F2 (normal)

Two genes, with a dominant allele at either or both loci. * P: AABB or aabb * F1: AaBb * F2 (lacerate): A_B_ or aaB_ or A_bb * F2 (normal): aabb

Multiple sclerosis (MS) is controlled by multiple autosomal loci, making it a complex disease to understand and treat. One interesting fact about the disease is that when one twin in a set of genetically identical twins develops MS, there is only a 25% chance that the other twin will also develop MS. This is an example of:

Variable penetrance

Define Epistasis

When one locus effects or covers the outcome of another locus

When conducting his initial genetic experiments, Gregor Mendel chose the pea plant as his research organism. He began conducting his genetic research on pea plant traits such as plant height, seed color, and seed shape. He started by using true-breeding, or pure-breeding, lines of pea plants. Select the characteristics of a true-breeding plant line.

When self-fertilized, all of the offspring show the trait of interest. In most cases, is homozygous for the trait of interest.

You cross a curly-winged female fruit fly with a straight-winged male fruit fly and get all straight-winged females and all curly-winged males. The next month you repeat the cross, this time using a curly-winged male fruit fly and a straight-winged female and get all straight-winged offspring. Assume the starting parents in each cross are true-breeding. What is the mode of inheritance for the allele controlling curly wings in fruit flies?

X-linked; curly recessive to straight

What demonstrates that a single X chromosome is sufficient for human development and survival?

XO

Which of the following will tend to lose genes over evolutionary time due to sex chromosome degeneration?

Y chromosomes (mammals) and W chromosomes (birds)

Is it possible for a male to have different color-blindness phenotypes in each eye?

Yes, in an XXY male with a different active X in each eye

In the case of a number of bird species, the male is homogametic rather than the female. This means that:

a ZW individual is female

Penile hypospadias, a birth defect in male humans in which the urethra opens on the shaft instead of at the tip of the penis, results from an autosomal dominant gene in some families. Females who carry the gene show no effects. What type of trait is this birth defect an example of?

a sex-limited trait because the defect occurs only in males and the gene involved is autosomal.