genetics 4: Mendel extended

Which statement best describes codominance?

A. One allele is partially functional while the other is not functional.

B. Both alleles contribute equally and visibly to the phenotype.

C. One allele completely masks the effect of the other.

D. The phenotype is an intermediate of the two alleles.

Both alleles contribute equally and visibly to the phenotype.

In a pedigree analysis, which assumption is valid for a rare autosomal recessive disorder?

A. Affected individuals must have at least one affected parent.

B. Unaffected individuals can be carriers.

C. Individuals marrying into the family are always carriers.

D. The disease allele is always dominant.

Unaffected individuals can be carriers.

Which of the following ratios is associated with recessive epistasis in dihybrid crosses?

A. 9:3:3:1

B. 1:2:1

C. 9:4:3

D. 12:3:1

9:4:3

What genetic explanation accounts for a 2:1 phenotypic ratio in a monohybrid cross involving coat color in mice?

• A. Codominance

• B. Incomplete dominance

• C. Lethal homozygous genotype

• D. Epistasis

Lethal homozygous genotype

Which of the following is not a feature of Mendel’s pea experiments that facilitated his discoveries?

• A. Traits controlled by multiple genes

• B. Dominant/recessive traits

• C. Traits not linked on chromosomes

• D. Phenotypes defined by single alleles

• Traits controlled by multiple genes

In the case of incomplete dominance, the phenotype of the heterozygous offspring is a(n) __________ of the two parental phenotypes.

intermediate

When two different mutant strains with the same phenotype produce wild-type offspring upon crossing, this is known as __________.

complementation

In a complementation test, if the offspring of two mutants are all still mutant, the mutations are likely in the __________ gene.

same

Penetrance is defined as the fraction of individuals with a particular __________ who display the expected phenotype.

genotype

When a dominant allele at one locus masks the expression of alleles at a second locus, the interaction is called __________ epistasis.

dominant

T/F: In pedigree analysis, X-linked traits affect males more frequently due to hemizygosity.

true

T/F: A polymorphic gene has many wild-type alleles in the population.

true

T/F: The presence of a recessive allele is enough to express a recessive trait in an individual.

false (Two recessive alleles are required for expression.)

Which phenotype ratio suggests additive interaction in a dihybrid cross?

• A. 1:2:1

• B. 9:3:3:1

• C. 9:4:3

• D. 12:3:1

• 9:3:3:1

Which of the following best defines pleiotropy?

• A. Two genes control one trait

• B. One gene affects multiple traits

• C. A single mutation causes a dominant phenotype

• D. All alleles are codominant

• One gene affects multiple traits

Which genotype combination is most likely for hearing parents to produce deaf children due to locus heterogeneity?

• A. aa x aa

• B. AA BB x aa bb

• C. Aa Bb x Aa Bb

• D. AA bb x aa BB

• AA bb x aa BB

In a pedigree for an X-linked recessive trait, which pattern is most likely observed?

• A. Trait appears only in females

• B. Affected fathers always pass the trait to sons

• C. Unaffected mothers can have affected sons

• D. All children of an affected mother are affected

• Unaffected mothers can have affected sons

What is the expected phenotypic ratio for dominant epistasis in dihybrid crosses?

• A. 9:3:3:1

• B. 9:4:3

• C. 1:2:1

• D. 12:3:1

• 12:3:1

In X-linked inheritance, a male receives his X chromosome exclusively from his __________.

mother

Expressivity refers to the __________ to which an individual with a genotype shows the associated phenotype.

degree

In the F2 generation of a cross with codominant alleles, the expected phenotypic ratio is __________.

1:2:1

Wild-type alleles are those that occur with a frequency greater than __________ in the population.

1%

T/F: Homozygous individuals with the Ay allele in mice survive and exhibit yellow fur.

false (Homozygous Ay individuals are lethal and do not survive.)

Which of the following statements is true regarding a dominant genetic trait?

• A) An unaffected individual can carry a dominant allele.

• B) An unaffected individual cannot have any alleles of the dominant trait.

• C) A single allele of the dominant trait does not affect the individual.

• D) Individuals with a single dominant allele will always be unaffected.

• An unaffected individual cannot have any alleles of the dominant trait.

In a family with a rare recessive genetic disorder, which of the following individuals can be a carrier of the disorder?

• A) An affected male.

• B) An unaffected female with two copies of the recessive allele.

• C) An unaffected male with one copy of the recessive allele.

• D) An unaffected female with one copy of the recessive allele.

• An unaffected female with one copy of the recessive allele.

Which of the following is correct about X-linked recessive traits?

• A) A male will be affected if he carries one allele of the X-linked recessive trait.

• B) A female needs two copies of the X-linked recessive allele to be affected.

• C) Both males and females need two copies of the X-linked recessive allele to show the trait.

• D) An affected male will pass the allele for an X-linked trait to all his daughters.

• A male will be affected if he carries one allele of the X-linked recessive trait.

Which of the following statements is true regarding the inheritance of X-linked traits?

• A) A father can pass an X-linked allele to both his sons and daughters.

• B) A mother can pass an X-linked allele to her sons but not to her daughters.

• C) A father passes an X-linked allele to his daughters but not to his sons.

• D) Only males can inherit X-linked traits.

• A father passes an X-linked allele to his daughters but not to his sons.

In a family, if the father is unaffected and the mother is a carrier of a recessive disorder, what is the likelihood that a daughter will be a carrier of the disorder?

• A) 25%

• B) 50%

• C) 75%

• D) 100%

• 50%

T/F: An unaffected individual cannot have any alleles of a recessive genetic trait.

false (An unaffected individual can still be a carrier of a recessive allele.)

T/F: A male with an X-linked recessive trait will pass this trait to all of his daughters.

true

T/F: An individual with one copy of a dominant allele for a disease will not be affected by the disease.

false (A dominant allele will result in the disease being expressed in the individual.)

Which of the following is TRUE about autosomal dominant inheritance?

• A) An affected individual must have an affected parent.

• B) An individual needs two copies of the dominant allele to express the trait.

• C) Autosomal dominant traits affect only one sex.

• D) An unaffected individual can pass on the dominant allele without showing the trait.

• An affected individual must have an affected parent.

In a family where one parent has Huntington’s disease (genotype Hh) and the other parent is unaffected (genotype hh), what is the probability that their child will inherit Huntington’s disease?

• A) 25%

• B) 50%

• C) 75%

• D) 100%

• 50%

What is the key feature of autosomal dominant inheritance?

• A) The trait appears only in males.

• B) Two copies of the allele are needed to express the trait.

• C) Affected individuals must have at least one affected parent.

• D) Only individuals with two dominant alleles will express the trait.

• Affected individuals must have at least one affected parent.

T/F: In autosomal dominant inheritance, two affected individuals can have an unaffected child.

true

T/F: In autosomal dominant inheritance, both males and females are equally likely to inherit the disorder.

true

Example of autosomal dominant disease?

Huntington’s disease

Which of the following is TRUE for autosomal recessive traits?

• A) Affected individuals must have one affected parent.

• B) Two copies of the recessive allele are required for an individual to be affected.

• C) Both males and females are affected in different proportions.

• D) An unaffected individual cannot pass on the recessive allele.

• Two copies of the recessive allele are required for an individual to be affected.

In a family with a child who has albinism (genotype aa), which of the following is most likely about the parents?

• A) Both parents are heterozygous carriers (Aa).

• B) One parent is heterozygous, and the other is homozygous dominant (AA).

• C) Both parents are homozygous dominant (AA).

• D) Both parents have albinism (aa).

• Both parents are heterozygous carriers (Aa).

If two individuals who are both carriers for albinism (genotype Aa) have children, what is the probability that their child will have albinism (aa)?

• A) 0%

• B) 25%

• C) 50%

• D 75%

• 25%

Which of the following is MOST likely to result in a higher incidence of autosomal recessive disorders in a population?

• A) High mutation rate of the gene causing the disorder.

• B) Large numbers of unaffected individuals.

• C) Close relatives marrying each other (consanguinity).

• D) Large number of heterozygous carriers.

• Close relatives marrying each other (consanguinity).

T/F: In autosomal recessive inheritance, a child with albinism will have parents who are both unaffected.

true

T/F: Albinism, as an autosomal recessive trait, affects males and females equally.

true

If an individual is not affected by an autosomal recessive disorder and has one parent who is a carrier (Aa) and one parent who is unaffected (AA), what is the probability that this individual is a carrier (Aa)?

A) 1/2
B) 1/3
C) 2/3
D) 1

2/3

When calculating the probability of an individual being a carrier for an autosomal recessive disease, and the individual is known to be unaffected, how many possibilities should be considered in the Punnett square?

• A) 2 possibilities: carrier or unaffected.

• B) 3 possibilities: unaffected, carrier, and affected.

• C) 4 possibilities: AA, Aa, Aa, aa.

• D) 5 possibilities: unaffected, carrier, affected, and two additional possibilities.

• 2 possibilities: carrier or unaffected.

If an individual is known to be unaffected by a recessive genetic disorder, and both parents are carriers (Aa), what is the probability that this individual is a carrier?

• A) 1/4

• B) 1/3

• C) 2/3

• D) 1/2

• 2/3

In incomplete dominance, the heterozygous offspring phenotype is:

• A) Identical to one of the parents.

• B) A mixture or blend of both parental phenotypes.

• C) Completely different from both parents.

• D) The same as the dominant parent.

• A mixture or blend of both parental phenotypes.

Which of the following is an example of incomplete dominance?

• A) Red flowers × white flowers producing red flowers.

• B) Tall plants × short plants producing plants of intermediate height.

• C) Black fur × white fur producing black fur.

• D) Purple flowers × purple flowers producing purple flowers.

Tall plants × short plants producing plants of intermediate height.

In a monohybrid cross between two organisms with incomplete dominance for flower color (red, white, and pink), what is the expected phenotypic ratio in the F2 generation?

• A) 1:1

• B) 3:1

• C) 1:2:1

• D) 2:1

• 1:2:1

Which pattern would most likely indicate an X-linked dominant disorder?

• A. Only males are affected

• B. Fathers transmit the disorder only to their daughters

• C. Affected males can have unaffected daughters

• D. Affected females never pass on the trait

• Fathers transmit the disorder only to their daughters

In co-dominance, the heterozygous offspring phenotype is:

• A) A blend of the two parental phenotypes.

• B) Identical to one of the parents.

• C) A combination where both parental traits appear simultaneously.

• D) Completely different from both parents.

• A combination where both parental traits appear simultaneously.

Which of the following is an example of co-dominance?

• A) Red flower × white flower producing pink flowers.

• B) Blood type AB in humans.

• C) Tall plants × short plants producing intermediate height.

• D) Huntington’s disease inheritance.

• Blood type AB in humans

If an individual with genotype IAIB for the ABO blood group system mates with an individual with genotype IAIA, what are the possible blood types of their children?

• A) Only type A.

• B) Type A and type B.

• C) Type A and type AB.

• D) Type AB only.

• Type A and type AB.

In a flower species showing co-dominance, crossing a red-flowered plant (RR) with a white-flowered plant (WW) results in offspring with red and white spotted flowers. What is the genotype of the offspring?

• A) RW

• B) RR

• C) WW

• D) WR (same as RW, but standard notation is RW)

• RW

Ratio of codominance inheritance

1:2:1

T/F: In additive gene interactions, heterozygous alleles can create a new phenotype that is different from both homozygous parents.

true

If two plants heterozygous for two additive seed color genes (AaBb × AaBb) are crossed, what is the expected genotypic ratio of the offspring?

• A) 1:2:1

• B) 9:3:3:1

• C) 3:1

• D) 1:1:1:1

• 9:3:3:1

In the agouti gene example, why is the observed phenotypic ratio 2 yellow : 1 grey instead of the expected 3:1?

• A) The yellow allele is recessive.

• B) The homozygous yellow (AyAy) genotype is lethal.

• C) The grey phenotype is dominant.

• D) There was an error in counting the offspring.

• The homozygous yellow (AyAy) genotype is lethal.

In the agouti gene case, the dominant Ay allele causes yellow fur color but also:

• A) Has no other effects.

• B) Causes increased survival of mice.

• C) Leads to lethality when homozygous.

• D) Is recessive to grey color.

• Leads to lethality when homozygous.

Explain why pleiotropy might cause unexpected phenotypic ratios in genetic crosses, using the agouti gene as an example.

Pleiotropy occurs when a gene influences multiple traits. In the agouti gene example, the dominant Ay allele causes yellow fur but is lethal when homozygous. Because homozygous AyAy mice do not survive, the typical Mendelian 3:1 ratio for a dominant trait is altered to 2:1 in living offspring.

In recessive epistasis, one gene can override the expression of another gene. In the case of labrador retrievers, the gene that overrides the other is the:

• A) B gene

• B) E gene

• C) A gene

• D) C gene

• E gene

In a dihybrid cross between two labrador retrievers, what phenotypic ratio is observed in the F2 generation, due to recessive epistasis?

• A) 9:3:3:1

• B) 9:4:3

• C) 1:2:1

• D) 3:1

• 9:4:3

Why does the F2 generation of labrador retrievers with recessive epistasis display a 9:4:3 ratio instead of the expected 9:3:3:1?

• A) The dominant allele of the B gene is not expressed.

• B) The homozygous recessive ee genotype overrides the B gene expression.

• C) The gene E is dominant over gene B.

• D) There is incomplete dominance between genes E and B

• The homozygous recessive ee genotype overrides the B gene expression.

In the labrador retriever example, what is the genotype for a yellow lab?

• A) B_E_

• B) bbE_

• C) B_B_

• D) ee

• ee

In recessive epistasis, the epistatic gene must be homozygous recessive to override the other gene.

true

In labrador retrievers, the E gene is epistatic, meaning that when the genotype is ee, it will prevent the expression of the B gene, leading to a yellow lab phenotype.

true

If a dog has a genotype of ee, the phenotype will be __________, even if it carries the B or b alleles.

yellow

If a labrador retriever has the genotype Ee and bb, what will its fur color be?

• A) Black

• B) Brown

• C) White

• D) Yellow

• Brown

11. In labrador retrievers, the E gene is required to produce __________, the pigment responsible for black coloration.

Eumelanin

The B gene is responsible for the __________ of Eumelanin in the fur.

deposition

A dog with the genotype Bb and Ee will have __________ fur if the genes are both functional.

black

How do the E and B genes interact to determine the fur color of labrador retrievers, and how does recessive epistasis play a role in this interaction?

The E gene is essential for producing Eumelanin, and the B gene is responsible for depositing it in the fur. If a dog has at least one E allele and a dominant B allele, it will be black. If the B allele is homozygous recessive (bb), the dog will have brown fur due to reduced deposition of Eumelanin. However, if the dog has two recessive e alleles (ee), it cannot produce Eumelanin at all, so the dog will be white, regardless of the B allele. This is an example of recessive epistasis, where the ee genotype masks the expression of the B gene.

In squash fruit, if the genotype is B_, what color will the squash be, regardless of the alleles at the second gene locus?

• A) Yellow

• B) Green

• C) White

• D) Orange

• White

In the squash fruit example, which gene is considered epistatic?

• A) Gene A

• B) Gene B

• C) Gene C

• D) Gene D

• Gene B

In the squash fruit example, what is the phenotypic ratio observed in the F2 generation?

• A) 9:3:3:1

• B) 9:7

• C) 12:3:1

• D) 3:1

• 12:3:1

If a squash has the genotype bb and A_, what color will the fruit be?

• A) White

• B) Green

• C) Yellow

• D) Orange

• Yellow

If a squash has the genotype bb and aa, it will appear green because there is no dominant allele to mask the green phenotype.

true

Explain why squash fruits with the genotype B_ will always be white, regardless of the genotype at the A gene locus.

The B allele is epistatic, meaning it overrides the effects of the A allele. If the squash has at least one dominant B allele (B_), the fruit will appear white, regardless of whether it has the A allele for yellow or the a allele for green.

In the squash fruit example, what is the role of gene A?

• A) It blocks pigment deposition.

• B) It converts green pigment into yellow pigment.

• C) It produces yellow pigment.

• D) It determines the squash's shape.

• It converts green pigment into yellow pigment.

What is the function of the B gene in the squash fruit example?

• A) It controls pigment production.

• B) It blocks pigment deposition, causing the squash to appear white.

• C) It produces the green pigment.

• D) It converts green pigment into yellow pigment.

• It blocks pigment deposition, causing the squash to appear white.

In the squash fruit example, if a squash has the genotype aa and bb, what color will the fruit be?

• A) White

• B) Green

• C) Yellow

• D) Red

green

What is locus heterogeneity?

• A) The phenomenon where a single gene mutation causes multiple phenotypes.

• B) The phenomenon where mutations in two or more genes result in the same phenotype.

• C) The phenomenon where one gene can compensate for a mutation in another gene.

• D) The phenomenon where mutations in different genes result in completely different phenotypes.

• The phenomenon where mutations in two or more genes result in the same phenotype.

n the context of the sweet pea flower example, mutations in either gene A or gene B result in the same phenotype (white flowers). This is an example of:

• A) Epistasis

• B) Locus Heterogeneity

• C) Dominant Inheritance

• D) Codominance

• Locus Heterogeneity

What does a complementation test determine?

• A) Whether two mutations affect the same gene or different genes.

• B) The exact location of a gene on a chromosome.

• C) The dominant or recessive nature of a trait.

• D) Whether a mutation will lead to a dominant phenotype.

Whether two mutations affect the same gene or different genes.

What is the expected outcome of a complementation test if two mutant strains with the same phenotype are crossed and the progeny are all wild type?

• A) The mutations are in the same gene.

• B) The mutations are in different genes.

• C) The mutations have no effect.

• D) The progeny will exhibit incomplete dominance.

• The mutations are in different genes.

If two mutant strains with the same phenotype are crossed and all progeny show the mutant phenotype, what does this suggest about the mutations?

• A) The mutations are in the same gene.

• B) The mutations are in different genes.

• C) The mutations complement each other.

• D) The mutation is recessive.

• The mutations are in the same gene.

Locus heterogeneity occurs when mutations in different genes result in the same phenotype.

true

In the context of human deafness, what does it mean when two deaf parents have hearing children?

• A) The deafness is caused by mutations in the same gene.

• B) The deafness is caused by mutations in different genes.

• C) The mutations are all dominant.

• D) Deafness is linked to the X chromosome.

• The deafness is caused by mutations in different genes.

If two deaf individuals have children who can hear, what genetic phenomenon is occurring?

• A) Non-complementation

• B) Epistasis

• C) Complementation

• D) Codominance

• Complementation

What are the parental genotypes if two deaf individuals with mutations in different genes have children who can hear?

• A) AA bb x aa BB

• B) aa BB x AA BB

• C) aa x aa

• D) Aa Bb x Aa Bb

AA bb x aa BB

In the case where two deaf parents have children who cannot hear, what can be concluded about the cause of the deafness?

• A) Deafness is due to mutations in different genes.

• B) Deafness is due to mutations in the same gene.

• C) The mutation is dominant.

• D) The mutation is X-linked.

• Deafness is due to mutations in the same gene.

What is the term used to describe the fraction of individuals with a specific genotype who express the associated phenotype?

• A) Expressivity

• B) Penetrance

• C) Incomplete Dominance

• D) Codominance

• Penetrance

Which of the following describes a situation where individuals with the same genotype show different degrees of severity of a phenotype?

• A) Penetrance

• B) Expressivity

• C) Gene Modifiers

• D) Epistasis

• Expressivity

f a disease allele causes a specific disease in some individuals but not in others who share the same genotype, this is an example of:

• A) Incomplete Penetrance

• B) Variable Expressivity

• C) Locus Heterogeneity

• D) Epistasis

• Incomplete Penetrance

Which of the following is a factor that can influence the expressivity of a phenotype?

• A) The presence of a dominant allele

• B) Environmental factors and modifier genes

• C) The mutation type (insertion vs. deletion)

• D) The location of the gene on the chromosome

• Environmental factors and modifier genes