BIOL1009- Topic 14+15

The chromosome theory of inheritance states that _____.

genes occupy specific positions on chromosomes homologous chromosomes segregate from each other during meiosis chromosomes assort independently during meiosis

If a plant variety is true-breeding for a dominant trait, then _____.

if the plant were allowed to self-pollinate, all of the progeny would have the dominant trait

During meiosis, homologous chromosomes sometimes "stick together" and do not separate properly. This phenomenon is known as _____.

nondisjunction

A linkage map _____.

orders genes on a chromosome based on recombination frequencies

Which of the following describes the sequence of events that occurs during DNA replication of a double-stranded DNA molecule?

separation of the DNA strands at DNA replication origins, unwinding of the DNA double helix, synthesis of RNA primers, synthesis of DNA, ligation of DNA fragments

Physically, what are different alleles?

Different alleles are different DNA sequences found at the same locus (location) on homologous chromosomes.

Human blood groups are governed by three alleles, A, B, and O. A and B are codominant and O is recessive to both. Which of the following matings cannot produce a child with blood type O? The letters refer to blood types (phenotypes).

O x AB

The ends of linear chromosomes are known as

Telomeres

Pea flowers may be purple (P) or white (p). Pea seeds may be round (R) or wrinkled (r). What proportion of the offspring from the cross PpRr x PpRr will have white flowers and wrinkled seeds?

1/16

Michelle and Keith are apparently normal, but their daughter was born with alkaptonuria, an inherited metabolic disorder. If alkaptonuria is like most other human hereditary disorders, the probability of their next child being born with alkaptonuria is _____.

1/4

The pedigree below is for a family, some of whose members exhibit the dominant trait, W. Affected individuals are indicated by a dark square or circle. What is the probability that individual III-1 is Ww?

100%

Hemophilia is a sex-linked disorder. The daughter of a father with hemophilia and a carrier mother has a _____ probability of having hemophilia.

50%

The pedigree below is for a family, some of whose members exhibit the dominant trait, W. Affected individuals are indicated by a dark square or circle. What is the likelihood that the progeny of IV-3 and IV-4 will have the trait?

50%

When crossing an organism that is homozygous recessive for a single trait with a heterozygote, what is the chance of producing an offspring with the homozygous recessive phenotype?

50%

Radish flowers may be red, purple, or white. A cross between a red-flowered plant and a white-flowered plant yields all-purple offspring. The part of the radish we eat may be oval or long, with long being the dominant characteristic. If true-breeding red long radishes are crossed with true-breeding white oval radishes, which of the following phenotypic ratios would be expected in the F2 generation?

6:3:3:2:1:1

What do we mean when we use the terms monohybrid cross and dihybrid cross?

A dihybrid cross involves organisms that are heterozygous for two characters and a monohybrid cross involves only one.

Why are individuals with an extra chromosome 21, which causes Down syndrome, more numerous than individuals with an extra chromosome 3 or chromosome 16?

Extra copies of the other chromosomes are probably fatal to the developing embryo.

A man who can roll his tongue and a woman who cannot roll her tongue have a son who can roll his tongue (R = can roll tongue; r = can't roll tongue). The son is curious about whether his father is homozygous or heterozygous for the tongue-rolling trait. Which of the following facts would allow him to know?

His father's mother cannot roll her tongue.

Why are there concerns about using increased telomerase activity to slow down the aging process?

One concern is that increasing telomerase activity could increase cancer rates.

What is meant by the description "antiparallel" regarding the strands that make up DNA?

The 5' to 3' direction of one strand runs counter to the 5' to 3' direction of the other strand.

Which of the following statements is true of linkage?

The closer two genes are on a chromosome, the lower the probability that a crossover will occur between them.

A red-eyed female fly was crossed with a white-eyed male fly. All the F1 offspring had red eyes. Two of these red-eyed F1 generation flies were crossed to each other. The F2 generation included both red- and white-eyed flies. Remarkably, all the white-eyed flies were male. What was the explanation for this result?

The gene involved is on the X chromosome.

Cystic fibrosis, which is usually lethal before the age of reproduction, is a homozygous recessive trait. Why do cases continue to arise, even though people with the disease rarely live to reproduce?

The harmful allele "hides" within heterozygous individuals, and one-fourth of the offspring of two heterozygotes would be afflicted.

In humans, which chromosome combinations normally determine whether an individual is biologically female or male?

XX individuals are biologically female, XY individuals are biologically male

An individual who is heterozygous at a given genetic locus for a recessively inherited disorder is known as a

carrier

The reaction used to join together nucleotides to form a nucleotide chain is known as a

dehydration reaction

Genotype:

describes the genes (or alleles of genes) carried by a particular individual.

Which of the following types of RNA molecules have polyA tails?

eukaryotic mRNA molecules

The recombination frequency between two gene loci is ____

greater as the distance between the two loci increases

If an organism has two identical alleles of a particular gene, the organism is

homozygous for that gene

Males are more often affected by sex-linked traits than females because

males only have one copy of the X chromosome.

"X inactivation" refers to

the inactivation of most of the genes on one X chromosome in genetic females

In certain plants, tall is dominant to short. If a heterozygous plant is crossed with a homozygous tall plant, what is the probability that the offspring will be short?

0

In the cross AaBbCc × AaBbCc, what is the probability of producing the genotype AABBCC?

1/64

Two true-breeding stocks of pea plants are crossed. One parent has red, axial flowers and the other has white, terminal flowers; all F1 individuals have red, axial flowers. The genes for flower color and location assort independently. If 1,000 F2 offspring resulted from the cross, approximately how many of them would you expect to have red, terminal flowers?

190

In a certain plant, the alleles A, B, and C are completely dominant to the alleles a, b, and c. A plant with the genotype AABbcc will have the same phenotype as a plant with the genotype _____.

AaBBcc

Recombination between linked genes comes about for what reason?

Crossovers between these genes result in chromosomal exchange.

Which of the following enzymes removes the RNA nucleotides from the primer and adds equivalent DNA nucleotides to the 3' end of DNA fragments resulting from DNA replication of one of the two DNA strands?

DNA polymerase 1

Sturtevant provided genetic evidence for the existence of four pairs of chromosomes in Drosophila in which of these ways?

Drosophila genes cluster into four distinct groups of linked genes.

In a nucleosome, the DNA is wrapped around

Histones

Red-green color blindness is a sex-linked recessive trait in humans. Two people with normal color vision have a color-blind son. What are the genotypes of the parents?

XCXc and XCY

Which of the following will happen to your chromosomes as you become older?

Your chromosomes will become shorter.

When a person has Down syndrome, he or she has an extra chromosome 21. Therefore, Down syndrome is a kind of _____ and results from _____.

aneuploidy ... nondisjunction of chromosome 21 during meiosis I

The progeny of a cross between two individuals of the "parental generation" are known as

the F1 generation.

If two genes are linked, _____.

they are on the same chromosome

In cats, black fur color is caused by an X-linked allele; the other allele at this locus causes orange color. The heterozygote is tortoiseshell. What kinds of offspring would you expect from the cross of a black female and an orange male?

tortoiseshell females; black males

If a heterozygous plant is allowed to self-pollinate, what proportion of the offspring will also be heterozygous?

1/2

Given the parents AABBCc × AabbCc, assume simple dominance for each trait and independent assortment. What proportion of the progeny will be expected to phenotypically resemble the first parent?

3/4

An Okazaki fragment has which of the following arrangements?

5' RNA nucleotides, DNA nucleotides 3'

Between which two genes would you expect the highest frequency of recombination A-W= 5 W-E= 3 E-G= 12 A-G= 20

A and G

The process by which DNA molecules are copied so that when cells divide each cell can have a complete copy of the DNA is known as

DNA Replication

Queen Victoria was a carrier of a recessive sex-linked allele for hemophilia. Which of the following possibilities could explain the presence of the hemophilia allele in her genotype?

Either her mother was a carrier or her father had hemophilia.

A woman is red-green color-blind. What can we conclude, if anything, about her father?

He is red-green color-blind.

X-linked genes differ from Y-linked genes in which of the following ways?

Sons and daughters have equal probabilities in inheriting a recessive allele of an X-linked gene from their mother, but only sons can inherit rare Y-linked genetic disorders from their father.

Why do some scientists feel that telomerase might be used to slow the aging process?

Telomere extension in mice and worms has reversed some signs of aging.

How would one explain a testcross involving F1 dihybrid flies in which more parental-type offspring than recombinant-type offspring are produced?

The two genes are closely linked on the same chromosome.

What does a frequency of recombination of 50% indicate?

The two genes are likely to be located on different chromosomes.

Alternative versions of a gene are known as

alleles

In a series of mapping experiments, the recombination frequencies for four different linked genes of Drosophila were determined as shown in the figure below. What is the order of these genes on a chromosome map?

b-rb-cn-vg

Homologous pairs of chromosomes often _____.

contain different alleles

Radish flowers may be red, purple, or white. A cross between a red-flowered plant and a white-flowered plant yields all-purple offspring. The part of the radish we eat may be oval or long, with long being the dominant characteristic. The flower color trait in radishes is an example of which of the following?

incomplete dominance

If the phenotype of a heterozygote is intermediate between the phenotypes of individuals homozygous for either allele, the alleles carried by that heterozygote must be what type of alleles?

incompletely dominant alleles

Increasing the affinity of RNA polymerase for the promoter of a particular gene will

increase the rate at which that gene is transcribed.

An allele whose phenotypic effect is not observed in a heterozygote is a

recessive allele

Wild type refers to _____.

the most common phenotype thought to be found in the natural population

Why did Mendel continue some of his experiments to the F2 or F3 generation?

to observe whether or not a recessive trait would reappear

Mendel accounted for the observation that traits which had disappeared in the F1 generation reappeared in the F2 generation by proposing that

traits can be dominant or recessive, and the recessive traits were obscured by the dominant ones in the F1.

Black fur in mice (B) is dominant to brown fur (b). Short tails (T) are dominant to long tails (t). What fraction of the progeny of crosses BbTt× BBtt will be expected to have black fur and long tails?

½

An individual with the genotype AABbCcDD can make how many different kinds of gametes?

4

Human blood groups are governed by three alleles, A, B, and O. A and B are codominant and O is recessive to both. If a woman with type O blood is expecting a child. Her husband is type A. Both the woman's father and her husband's father had type B blood. What is the probability that the child will have type O blood?

50%

What is the difference between "genotype" and "phenotype"?

Genotype refers to which genes, or which alleles of a particular gene, are carried by an individual. Phenotype refers to the traits exhibited by an individual.

The two strands of a double-stranded DNA molecule are held together by

Hydrogen bonds.

Map units on a linkage map cannot be relied upon to calculate physical distances on a chromosome for which of the following reasons?

The frequency of crossing over varies along the length of the chromosome.

A genetic defect in humans results in the absence of sweat glands in the skin. Some men have this defect all over their bodies, but in women it is usually expressed in a peculiar way: A woman with this defect typically has small patches of skin with sweat glands and other patches without sweat glands. In women, the pattern of sweat-gland distribution can best be explained by _____.

X chromosome inactivation

When a ribosome reaches the end of the coding region of an mRNA molecule, so that a stop codon is in the A site of the ribosome,

a release factor binds the stop codon at the A site and the polypeptide is freed from the tRNA in the P site

Assume tall (T) is completely dominant to dwarf (t) in a certain species of plant. If a homozygous dominant individual is crossed with a homozygous dwarf, the offspring will _____.

all be tall

A "Barr body" is

an inactive X chromosome

The elongation of the leading strand during DNA synthesis

depends on the action of DNA polymerase.

Drosophila (fruit flies) usually have long wings, but mutations in the BTgene can result in bent wings and mutations in the VG gene can result in vestigial wings. If flies that are heterozygous for both the bent wing gene and the vestigial wing gene are mated, what is the probability of offspring with bent wings only? Note that the mutant alleles of both genes are recessive.

3/16

Two true-breeding stocks of pea plants are crossed. One parent has red, axial flowers and the other has white, terminal flowers; all F1 individuals have red, axial flowers. The genes for flower color and location assort independently. Among the F2 offspring, what is the probability of plants with white axial flowers?

3/16

Why did the F1 offspring of Mendel's classic pea cross always look like one of the two parental varieties?

One phenotype was completely dominant over another.

What was the most significant conclusion that Gregor Mendel drew from his experiments with pea plants?

Traits are inherited in discrete units, and are not the results of "blending."

In a particular plant, leaf color is controlled by gene locus D. Plants with at least one allele D have dark green leaves, and plants with the homozygous recessive dd genotype have light green leaves. A true-breeding dark-leaved plant is crossed with a light-leaved one, and the F1 offspring is allowed to self-pollinate. The predicted outcome of the F2 is diagrammed in the Punnett square shown in the figure below, where 1, 2, 3, and 4 represent the genotypes corresponding to each box within the square. Which of the plants will be true-breeding?

1 and 4 only

An AABbccDdEeFFindividual is crossed with an individual with the genotype AaBBCCDdEeff. What is the probability that their offspring will have the genotype AaBBCcddEEFf?

1/64

If each parent can produce 100 genetically distinct gametes, how many genetically distinct offspring can two parents produce?

10,000

Cinnabar eyes is a sex-linked recessive characteristic in fruit flies. If a female having cinnabar eyes is crossed with a wild-type male, what percentage of the F1 males will have cinnabar eyes?

100%

In a particular plant, leaf color is controlled by gene locus D. Plants with at least one allele D have dark green leaves, and plants with the homozygous recessive dd genotype have light green leaves. A true-breeding dark-leaved plant is crossed with a light-leaved one, and the F1 offspring is allowed to self-pollinate. The predicted outcome of the F2 is diagrammed in the Punnett square shown in the figure below, where 1, 2, 3, and 4 represent the genotypes corresponding to each box within the square. Which of the boxes marked 1-4 correspond to plants with a heterozygous genotype?

2 and 3

How many unique gametes could be produced through independent assortment by an individual with the genotype AaBbCCDdEE?

8

Human blood groups are governed by three alleles, A, B, and O. A and B are codominant and O is recessive to both. A man who has type B blood and a woman who has type A blood could have children of which of the following phenotypes?

A, B, AB, or O

A = big apples ;R = red apples; a = small apples; r = yellow apples. You have one tree that produces big yellow apples and another tree that produces small red apples. When the two are crossed, you find that half of the new trees produce big red apples and half produce big yellow apples. What are the genotypes of the parents?

AArr and aaRr

If an experimenter moves the repressor gene (lac I) for the lac operon, along with its promoter, to a position some several thousand base pairs away from its normal position in the lac operon, which will you expect to occur?

The lac operon will function normally.

Pea plants are tall if they have the genotype TT or Tt, and they are short if they have genotype tt. A tall plant is mated with a short plant. Which outcome below would indicate that the tall parent plant was heterozygous?

The ratio of tall offspring to short offspring is 1:1.

Duchenne muscular dystrophy is caused by a sex-linked recessive allele. Its victims are almost invariably boys, who usually die before the age of 20. Why is this disorder almost never seen in girls?

To express an X-linked recessive allele, a female must have two copies of the allele.

Drosophila (fruit flies) usually have long wings, but mutations in the BTgene can result in bent wings and mutations in the VG gene can result in vestigial wings. If a homozygous bent wing fly is mated with a homozygous vestigial wing fly, which of the following offspring would you expect? Note that flies that have one wild-type allele and one mutant allele of the BTgene are represented by +bt, and flies that have one wild-type allele and one mutant allele of the VG gene are represented by +vg.

all +bt +vg heterozygotes

If you cross a plant that is homozygous for the recessive allele of a trait with a plant that is homozygous for the dominant allele of the same trait, the F1 generation will differ from the F2 in that _____.

all of the F1 will show the dominant phenotype, but only three-fourths of the F2 will

The fact that plants can be cloned from many different types of cells demonstrates that

differentiated cells retain all the genes of the zygote.

If an organism has two different alleles of a particular gene, the organism is

heterozygous for that gene

If a plant variety is true-breeding for a dominant trait, then _____

if the plant were allowed to self-pollinate, all of the progeny would have the dominant trait

Because the frequency of crossing over is not uniform along the length of a chromosome, _____.

map units do not necessarily correlate to physical distances along the chromosome

Radish flowers may be red, purple, or white. A cross between a red-flowered plant and a white-flowered plant yields all-purple offspring. The part of the radish we eat may be oval or long, with long being the dominant characteristic. If true-breeding red long radishes are crossed with true-breeding white oval radishes, the F1 will be expected to be which of the following?

purple and long

It is far more common to find human genetic disease caused by _____ alleles than by _____ alleles because _____.

recessive ... dominant ... harmful recessive alleles can survive in the heterozygote without any selection pressure against them

Which of the following would result in genetic variation by way of new combinations of alleles?

the exchange of alleles between homologous chromosomes during meiosis I independent alignment of homologous chromosomes during meiosis I random fertilization increasing the number of possible allele combinations in an individual