Genetics chaoter 4 flashcards

Flashcards covering non-Mendelian inheritance, alleles, mutations, incomplete dominance, codominance, multiple alleles, lethal alleles, epistasis, pleiotropy, and X-linked inheritance.

What is an allele?

An alternative form of the same gene.

What is a wild-type allele?

The allele that occurs most frequently in a population.

Is the wild-type allele always dominant?

No. It may be dominant, but not always.

What is a mutant allele?

An allele containing modified genetic information that often produces an altered gene product.

What are the three types of functional changes caused by mutations?

Loss-of-function, gain-of-function, and neutral mutations.

What is a loss-of-function mutation?

A mutation that reduces or eliminates gene function.

What is a null allele?

An allele resulting from a complete loss of gene function.

What is a gain-of-function mutation?

A mutation that enhances or increases the function of the wild-type allele.

What type of inheritance does a gain-of-function mutation generally produce?

Dominant inheritance.

What is a neutral mutation?

A mutation that causes no change in phenotype.

What does an uppercase allele symbol usually represent?

A dominant allele.

What does a lowercase italic allele symbol usually represent?

A recessive allele.

In Drosophila notation, what does the "+" symbol represent?

The wild-type allele.

In Drosophila, what does e represent?

The recessive ebony mutant allele.

What is the genotype of a homozygous wild-type gray Drosophila?

e⁺/e⁺ or +/+.

What is the genotype of a heterozygous gray Drosophila?

e⁺/e or +/e.

What is the genotype of an ebony Drosophila?

e/e.

If e/e is ebony and e⁺/e is gray, what does this tell you about e?

e is recessive to e⁺.

Is the "+" symbol automatically the dominant allele?

No. "+" identifies the wild-type allele; dominance is determined separately.

What is incomplete dominance?

Neither allele is completely dominant, producing an intermediate heterozygous phenotype.

What is codominance?

Both alleles are fully and simultaneously expressed in the heterozygote.

Does codominance produce a blended phenotype?

No.

What is the difference between incomplete dominance and codominance?

Incomplete dominance produces an intermediate phenotype; codominance expresses both phenotypes together.

What is an example of codominance in humans?

The MN blood group.

What determines the MN blood type?

M and N glycoprotein antigens on red blood cells.

What phenotype does an MᴹMᴹ individual have?

M blood type.

What phenotype does an MᴺMᴺ individual have?

N blood type.

What phenotype does an MᴹMᴺ individual have?

MN blood type.

What happens when two MN individuals are crossed?

They can produce M, MN, and N offspring.

What is the expected genotypic ratio from two MN heterozygotes?

1 MᴹMᴹ : 2 MᴹMᴺ : 1 MᴺMᴺ.

What is the expected phenotypic ratio from two MN heterozygotes?

1 M : 2 MN : 1 N.

What is the F₂ phenotypic ratio for incomplete dominance?

1 parental phenotype : 2 intermediate : 1 other parental phenotype.

Why are the genotypic and phenotypic ratios the same in incomplete dominance?

Each genotype produces its own distinct phenotype.

If red snapdragons are crossed with white snapdragons and the F₁ offspring are pink, what inheritance pattern is shown?

Incomplete dominance.

If two pink snapdragons are crossed, what fraction of the offspring are expected to be pink?

$$\frac{1}{2}$$

If two pink snapdragons are crossed, what fraction are expected to be red?

$$\frac{1}{4}$$

If two pink snapdragons are crossed, what fraction are expected to be white?

$$\frac{1}{4}$$

If a heterozygote displays both parental traits simultaneously rather than an intermediate phenotype, what inheritance pattern is shown?

Codominance.

What are multiple alleles?

Three or more alleles of the same gene in a population.

What is an example of multiple alleles in humans?

The ABO blood group system.

What are the three alleles for the ABO blood group gene?

Iᴬ, Iᴮ, and i.

What does the Iᴬ allele produce?

The A antigen.

What does the Iᴮ allele produce?

The B antigen.

What does the i allele produce?

No antigen.

What is the relationship between Iᴬ and i?

Iᴬ is dominant to i.

What is the relationship between Iᴮ and i?

Iᴮ is dominant to i.

What is the relationship between Iᴬ and Iᴮ?

They are codominant.

What genotype produces type A blood?

IᴬIᴬ or Iᴬi.

What genotype produces type B blood?

IᴮIᴮ or Iᴮi.

What genotype produces type AB blood?

IᴬIᴮ.

What genotype produces type O blood?

ii.

Why can a person with IᴬIᴮ genotype have type AB blood?

Iᴬ and Iᴮ are codominant, so both antigens are expressed.

Why does ii produce type O blood?

The i allele produces no antigen, so an ii individual has neither A nor B antigen.

What blood type does an Iᴬi person have?

Type A.

What blood type does an Iᴮi person have?

Type B.

What blood type does an IᴬIᴮ person have?

Type AB only.

What blood type does an ii person have?

Type O only.

Why can multiple alleles only be studied at the population level?

One individual can have only two alleles of a gene, even though more than two exist in the population.

What two inheritance concepts are demonstrated by the ABO system?

Multiple alleles and codominance.

Can a type A person have genotype IᴬIᴬ or Iᴬi?

Yes.

Can a type B person have genotype IᴮIᴮ or Iᴮi?

Yes.

Can a type AB person have an i allele?

No; the AB genotype is IᴬIᴮ.

Can a type O person have an Iᴬ or Iᴮ allele?

No; type O is ii.

Can two type A parents have a type O child?

Yes, if both parents are Iᴬi.

Can two type B parents have a type O child?

Yes, if both parents are Iᴮi.

Can an AB parent have a type O child?

No. An AB parent has no i allele to pass.

If an AB person is crossed with an O person, what blood types can their children have?

Type A or type B.

If an A mother has a type O son, what must be true about the mother's genotype?

She must be Iᴬi.

If a type A mother has a type O son, what must be true about the father?

He must carry an i allele.

If a type A mother has a type O son, what blood types could the father have?

A, B, or O, as long as he carries i.

If a type A mother has a type O son, could the father be AB?

No, because an AB father has no i allele.

What is an essential gene?

A gene that is absolutely required for survival.

What is a lethal allele?

An allele that has the potential to cause death.

What causes lethal alleles?

Mutations in essential genes.

What is a recessive lethal allele?

An allele that causes death when homozygous but can be tolerated in a heterozygote.

Why can a heterozygote survive with a recessive lethal allele?

One wild-type allele provides enough function for survival.

What happens to an individual homozygous for a recessive lethal allele?

It does not survive.

What is a dominant lethal allele?

An allele where one copy is sufficient to cause death.

What is the typical surviving offspring ratio from a cross of two heterozygotes carrying a recessive lethal allele?

2 with the trait : 1 without the trait.

What inheritance pattern is demonstrated by Huntington disease?

Autosomal dominant inheritance.

Can a heterozygous individual have Huntington disease?

Yes.

Why can Huntington disease be considered a dominant lethal condition?

One copy of the allele can eventually result in death.

When does Huntington disease typically become apparent according to the PowerPoint?

In adulthood.

What are major characteristics of Huntington disease?

Progressive nervous-system degeneration, dementia, and early death.

Why does a recessive lethal cross often produce a 2:1 ratio among surviving offspring?

The expected homozygous lethal class dies, leaving a 2:1 ratio among survivors.

What genotype is missing from the surviving offspring in a recessive lethal cross?

The homozygous lethal genotype.

If a cross theoretically produces 1/4 AA, 1/2 Aa, and 1/4 aa, but aa dies, what ratio is expected among survivors?

1 AA : 2 Aa.

If two short-tailed mice produce offspring in a 2 short : 1 long ratio, what should you suspect?

A recessive lethal allele.

How can an allele be dominant for one characteristic but recessive for another?

An allele can produce a dominant visible phenotype while being recessive for lethality.

Why can a dominant lethal allele persist in a population?

If its effects do not appear until adulthood, an individual may reproduce before the lethal phenotype appears.

Why would a dominant lethal allele appearing before reproduction tend to be eliminated more quickly?

Affected individuals would be less likely to reproduce.

What is gene interaction?

When several genes influence a particular characteristic.

Why can multiple genes influence one phenotype?

Their gene products work together in cellular processes that contribute to the phenotype.

What is epistasis?

When one gene masks or modifies the expression of another gene.

What is the Bombay phenotype?

A homozygous recessive condition in which a FUT1 mutation masks the expression of ABO alleles.

What gene is involved in the Bombay phenotype?

FUT1.

What happens when FUT1 is mutated in the Bombay phenotype?

The mutation masks the expression of the Iᴬ and Iᴮ alleles.

What type of genetic interaction does the Bombay phenotype demonstrate?

Epistasis.

Which gene is being masked by FUT1 in the Bombay phenotype?

The ABO gene.

What condition is required for the A and B antigens to be expressed?

At least one wild-type FUT1 allele must be present.