2nd exam chp 4

A mutation in a gene often results in a reduction of the product of that gene. The term for this type of mutation is ________.

Loss of function or null (in the case of complete loss)

Which mutations are generally dominant since one copy in a diploid organism is sufficient to alter the normal phenotype?

gain of function

Assume that a mutation occurs in the gene responsible for the production of hexosaminidase A, such that only about 50% of the enzyme activity is found in the heterozygote compared with a homozygous normal individual. If heterozygotes are phenotypically normal, we would say that the mutant allele is ________ to its normal allele.

recessive

What is the most prevalent form of an allele called?

wild type

T or F: A neutral mutation leads to no discernable phenotype.

T

Typically, when one wishes to represent a gene, the symbol used is ________.

in italics

With incomplete dominance, a likely ratio resulting from a monohybrid cross would be ________.

1:2:1

Assume that a dihybrid cross (AaBb × AaBb) is made in which the gene loci are autosomal, independently assorting, and incompletely dominant. What phenotypic ratio would you expect from such a cross?

1:2:1:2:4:2:1:2:1

Assume that a cross is made between two organisms that are both heterozygous for a gene that shows incomplete dominance. What phenotypic and genotypic ratios are expected in the offspring?

phenotypic 1:2:1; genotypic 1:2:1

Assume that a dihybrid cross is made in which the genes' loci are autosomal, independently assorting, and incompletely dominant. How many different phenotypes are expected in the offspring?

9

A ________ ratio indicates incomplete dominance.

1:2:1

The trait of medium-sized leaves in iris is determined by the genetic condition PP′. Plants with large leaves are PP, whereas plants with small leaves are P′P′. A cross is made between two plants each with medium-sized leaves. What is the term for this allelic relationship?

incomplete dominance

The trait of medium-sized leaves in iris is determined by the genetic condition PP′. Plants with large leaves are PP, whereas plants with small leaves are P′P′. A cross is made between two plants each with medium-sized leaves. If they produce 80 seedlings, what would be the expected phenotypes, and in what numbers would they be expected?

20 (large leaves), 40 (medium leaves), 20 (small leaves)

The trait for medium-sized leaves in iris is determined by the genetic condition PP′. Plants with large leaves are PP, whereas plants with small leaves are P′P′. The trait for red flowers is controlled by the genes RR, pink by RR′, and white by R′R′. A cross is made between two plants each with medium-sized leaves and pink flowers. If they produce 320 seedlings, what would be the expected phenotypes, and in what numbers would they be expected? Assume no linkage

20 large, red; 40 medium, red; 20 small, red; 40 large, pink; 80 medium, pink; 40 small, pink; 20 large, white; 40 medium, white; 20 small, white

T or F

Even in a seemingly clear-cut example of complete dominance, at the protein or enzyme level, one can detect about half the activity or gene product.

Which of the following is an example of codominance?

in roan cattle, you can see a mix or both red and white furs

What is the blood type of individuals who cannot add the terminal sugar to the H substance?

O

A situation in which there are more than two alternative forms of a given gene would be called ________.

multiple alleles

In a mating between individuals with the genotypes IAi × ii, what percentage of the offspring are expected to have the O blood type?

50%

In a mating between individuals with the genotypes IAIB × ii, what percentage of the offspring are expected to have the O blood type?

0%

With ________, there will be more than two genetic alternatives for a given locus.

multiple alleles

The ABO blood group locus in humans provides an example of ________.

multiple alleles

What would be a typical phenotypic monohybrid ratio in which a lethal allele is involved?

2:1

Achondroplasia is a form of human dwarfism. If two individuals with achondroplasia have children with the following ratio, 2 dwarf to 1 wild type, what is the means of inheritance of this phenotype?

dominant lethal

An allele of RNA polymerase in Drosophila demonstrates a recessive lethal inheritance pattern. Which of the following is true?

Homozygous recessive offspring will never be seen

A snapdragon plant has red, pink, or white flowers, inherited in an incomplete dominance pattern. It can come in tall or dwarf (homozygous recessive) varieties. What is the ratio expected if you cross a pink tall (heterozygous) plant with a pink short plant?

1 red tall : 1 red short : 2 pink tall : 2 pink short : 1 white tall : 1 white short

Rabbits can come in an allelic series where brown > himilayan > chinchilla > albino, where > means dominant over. They also can come in long (recessive) and short fur. You wish to obtain rabbit babies that are albino with long fur. Which of the following crosses would you do?

chinchilla heterozygous with albino with short fur (heterozygous) × brown heterozygous with albino with long fur

What term is used to express the idea that several genes exert influence over the same characteristic?

gene interaction

A condition in which one gene pair masks the expression of a nonallelic gene pair is called ________.

epistasis

Typical ratios resulting from epistatic interactions in dihybrid crosses would be ________.

9:3:4, 9:7

A mutant gene that produces brown eyes (bw) is located on chromosome #2 of Drosophila melanogaster, whereas a mutant gene producing bright red eyes, scarlet (st), is located on chromosome #3. Phenotypically, wild-type flies (with dull red eyes), whose mothers had brown eyes and whose fathers had scarlet eyes, were mated. The 800 offspring possessed the following phenotypes: wild type (dull red), white, scarlet (bright red), and brown. Most of the 800 offspring had wild-type eyes, whereas those with white eyes were the least frequent. From the information presented above, how many white-eyed flies would you expect in the F2 generation?

50

In the mouse, gene A allows pigmentation to be deposited in the individual coat hairs; its allele a prevents such deposition of pigment, resulting in an albino. Gene B gives agouti (wildtype fur); its allele b gives black fur. What would the expected ratio of the progeny be in a cross of a doubly heterozygous agouti mouse mated with a doubly homozygous recessive white mouse?

1 (agouti) :1 (black) : 2 (albino)

T or F: Epistasis would not be expected to occur in a biochemical pathway.

F

The following F2 results occur from a typical dihybrid cross: If a double heterozygote (AaBb) is crossed with a fully recessive organism (aabb), what phenotypic ratio is expected in the offspring?

1 purple : 3 white

Many of the color varieties of summer squash are determined by several interacting loci: AA or Aa gives white, aaBB or aaBb gives yellow, and aabb produces green. Assume that two fully heterozygous plants are crossed. Give the phenotypes (with frequencies) of the offspring

12 white : 3 yellow : 1 green

Which of the following ratio is not likely to occur in crosses (F2) when one is dealing with two interacting, epistatic gene pairs?

3:1

Assume that a dihybrid F2 ratio, resulting from epistasis, was 9:3:4. If a double heterozygote was crossed with the fully recessive type, what phenotypic ratio is expected among the offspring?

1:1:2

Assume that a dihybrid F2 ratio, resulting from epistasis, was 15:1. If a double heterozygote was crossed with the fully recessive type, what phenotypic ratio is expected among the offspring?

3:1

Comb shape in chickens represents one of the classic examples of gene interaction. Two gene pairs interact to influence the shape of the comb. The genes for rose comb (R) and pea comb (P) together produce walnut comb. The fully homozygous recessive condition (rrpp) produces the single comb. Assume that a rose-comb chicken is crossed with a walnut-comb chicken and the following offspring are produced: 17 walnut, 16 rose, 7 pea, and 6 single. What are the probable genotypes of the parents?

Rrpp × RrPp

Many of the color varieties of summer squash are determined by several interacting loci: AA or Aa gives white, aaBB or aaBb gives yellow, and aabb produces green. Crosses among heterozygotes give a 12:3:1 ratio. What type of gene interaction would account for these results?

epistasis

A particular cross gives a modified dihybrid ratio of 9:7. What phenotypic ratio would you expect in a testcross of the fully heterozygous F1 crossed with the fully recessive type?

1:3

When two squash plants with disc-shaped fruit are crossed, depending on the genotype of the parents, disc, sphere, and long fruits may be seen in the offspring. This is an example of ________.

two gene interaction with novel phenotypes

What is a heterogenous trait?

a trait in which many genes can potentially be mutated to lead to the same phenotype

Alleles that are masked by an epistatic locus are said to be ________ to the genes at that locus

hypostatic

Multiple mutations that are found to be present in a single gene are said to belong to the same ________ group.

complementation

Which of the following crosses would indicate that the mutants were in the same complementation group? (pattern)

pink eye fly × pink eye fly -> pink eye fl

What is the term for a gene mutation that leads to a myriad of disparate effects?

pleiotropy

With which of the following would hemizygosity most likely be associated?

X-linked inheritance

Because of the mechanism of sex determination, males of many species can be neither homozygous nor heterozygous. Such males are said to be ________

hemizygous

The white-eyed gene in Drosophila is recessive and sex-linked. Assume that a white-eyed female is mated to a wild-type male. What would be the phenotypes of the offspring?

females wild type, males white eyed

Two forms of hemophilia are determined by genes on the X chromosome in humans. Assume that a phenotypically normal woman whose father had hemophilia is married to a normal man. What is the probability that their first son will have hemophilia?

1/2

Two forms of hemophilia are determined by genes on the X chromosome in humans. Assume that a phenotypically normal woman whose father had hemophilia is married to a normal man. What is the probability that their first daughter will have hemophilia?

zero

The deficiency of the enzyme glucose-6-phosphate dehydrogenase (G6PD) is inherited as a recessive gene on the X chromosome in humans. A phenotypically normal woman (whose father had G6PD) is married to a normal man. What fraction of their sons would be expected to have G6PD?

1/2

If an X-linked disorder is lethal to the affected individual prior to the age at which one reaches reproductive maturation, the lethality will be expressed only in males. Why is this so?

The only sources of the lethal allele in the population are heterozygous females who are "carriers" and do not express the disorder

The genes for zeste eyes and forked bristles are located on the X chromosome in Drosophila melanogaster. Both genes are recessive. A cross is made between a zeste-eyed female and a forked-bristled male. If 200 offspring from this cross were obtained, what is the expected offspring's phenotype and sex?

100 wild female; 100 zeste male

T or F: Males are more liable to express recessive alleles as they are hemizygous.

T

What is a significant difference between X-linked and sex-influenced inheritances?

In X-linked inheritance, the gene in question is on the X chromosome; in sex-influenced inheritance, the gene is autosomal.

Name three modes of inheritance that are influenced by the sex of individuals.

X-linked, sex-influenced, sex-limited

Which of the following is an example of sex-limited inheritance?

beard formation in humans

A ________ is one whose expression is influenced by some environmental condition.

conditional mutant

T or F: Genomic anticipation refers to observations that a genetic disorder occurs at an earlier age in successive generations, whereas genetic imprinting occurs when gene expression varies depending on parental origin.

T

The accompanying figure is a pedigree of a fairly common human hereditary trait in which the boxes represent males and the circles represent females. Shading symbolizes the abnormal phenotype.

recessive, autosomal

A cross was made between homozygous wild-type female Drosophila and yellow-bodied male Drosophila. All of the resulting offspring were phenotypically wild type. Offspring of the F2 generation had the following phenotypes:

recessive, X linked