Ch. 15 Quiz (Bio) Exam 5

Mutant tetraploid plants _____.

are unable to interbreed with a diploid plant -This is why polyploidy is a mechanisms of plant speciation.

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

males are hemizygous for the X chromosome.

Genomic imprinting is generally due to the addition of methyl (-CH3) groups to C nucleotides in order to silence a given gene. If this depends on the sex of the parent who transmits the gene, which of the following must be true?

methylation must be reversible in ovarian testicular cells.

What is the source of the extra chromosome 21 in an individual with Down syndrome?

nondisjunction or translocation in either parent

A white-eyed female Drosophila is crossed with a red-eyed male Drosophila. Which statement below correctly describes the results?

none of the females will have white eyes. all of the females will have red eyes because they will inherit the dominant red-eye allele from their male parent.

Monosomy

one chromosome is missing, so the cell has only one copy of a particular chromosome. in humans, most monosomies are lethal. However, a female can survive with just one X chromosome, but she will have Turner syndrome.

Which of these terms applies to an organism with extra sets of chromosomes?

polyploid -polyploid individuals have more than two complete sets of chromosomes.

What name is given to the most common phenotype in a natural population?

wild type -the most common phenotype is the wild type

A particular diploid plant species has 48 chromosomes, or two sets. A mutation occurs and gametes with 48 chromosomes are produced. If self-fertilization occurs, the zygote will have _____ set(s) of chromosomes.

4 -If self-fertilization occurs, and two gametes (each having 48 chromosomes) unite, the zygote will have 96 chromosomes ( or 4 sets)

Of the following human aneuploidies, which is the one that generally has the most severe impact on the health of the individual?

47, +21

Humans are diploid and have 46 chromosomes (or two sets). How many sets of chromosomes are found in each human gamete?

1 -Meiosis cuts the number of chromosomal sets in half.

Humans are diploid and have 46 chromosomes. How many chromosomes are found in each human gamete?

23 -23 is one half of 46

Down Syndrome

A chromosomal disorder resulting from trisomy of chromosome 21. The syndrome is characterized by mental retardation, a high risk for heart problems and leukemia, and a degenerative brain disorder similar to Alzheimer's disease.

Trisomy

A condition in which a diploid cell or organism has an extra chromosome of one type, producing a chromosome number of 2n+1

Nondisjunction in Meiosis 1

A diploid cell that undergoes meiosis typically produces four haploid cells, which have precisely half the genetic material of the parent cell. The diploid cell has two complete sets of chromosomes, ad each of the haploid cells has a single complete set of chromosomes. Non disjunction refers to an error in cell division. In some cases homologous chromosomes do not separate from each other during cell division. In other cases, the problem occurs when sister chromatid do not separate from each other. Non disjunction can occur in mitosis or meiosis. If non disjunction occurs in meiosis 1, both chromosomes of a homologous pair migrate to the same pole, leaving one daughter cell without a chromosome. The cells go through meiosis 2 normally, producing four gametes with unusual numbers of chromosomes. Two gametes have one complete set of chromosomes plus one extra chromosome, indicated by n+1, the other two gametes lack a chromosome are designated n-1.

If a diploid cell undergoes meiosis and produces two gametes with n + 1 chromosomes and two gametes with n− 1 chromosomes, what type of error occurred?

A nondisjunction error occurred in meiosis I, in which both members of a homologous pair migrated to the same pole of the cell.

If a diploid cell undergoes meiosis and produces two gametes that are normal, and one with n − 1 chromosomes, and one with n + 1 chromosomes, what type of error occurred?

A nondisjunction error occurred in meiosis II, in which both sister chromatids of a chromosome migrated to the same pole of the cell.

What kind of cell results when a diploid and a haploid gamete fuse during fertilization?

A triploid cell. -A triploid cell has three sets of chromosomes: the two from the diploid gamete and the one from the haploid gamete.

A white-eyed female Drosophila is crossed with a red-eyed male Drosophila. Which statement below correctly describes the results?

An error in cell division that causes homologous chromosomes or sister chromatids to move to the same side of the dividing cell -Nondisjunction refers to the failure of pairs of chromosomes or sister chromatids to separate during meiosis or mitosis.

Which of the following results in a situation in which the chromosome number is either 2n+1 or 2n-1 ?

Aneuploidy An aneuploid individual has either too many or too few chromosomes, usually as a result of nondisjunction.

Recombination between linked genes comes about for what reason?

Crossovers between these genes result in chromosomal exchange.

_____ is the process by which haploid gametes form a diploid zygote.

Fertilization -the joining of haploid gametes produces a diploid zygote.

How are human mitochondria inherited?

From the mother only. -An individuals mitochondria are all derived from those found in the ovum.

Aneuploid

Having a chromosome number that is not an exact multiple of the normal diploid number, with either more or fewer than the normal number of chromosomes in the cell. Trisomy (having an extra chromosome) and monosomy (missing a chromosome) are examples.

Polyploid

Having more than two sets of chromosomes. Triploidy, in which an organism has three complete sets of chromosomes, is an example.

When can nondisjunction occur? Choose the best answer.

Nondisjunction errors can occur in meiosis I, when homologous chromosomes fail to separate, or in either mitosis or meiosis II, when sister chromatids fail to separate.

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.

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.

When Thomas Hunt Morgan crossed his red-eyed F1 generation flies 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

Which of the following is true of an X-linked gene, but not of a Y-linked gene?

The gene is present in both males and females.

In humans, what determines the sex of offspring and why?

The male gamete determines sex because each male gamete can contribute either an X or a Y chromosome. -In humans, the male produces both X- and Y-bearing sperm, whereas females only produce X-bearing eggs.

One possible result of chromosomal breakage is for a fragment to join a nonhomologous chromosome. What is this alteration called?

Translocation

Of the following chromosomal abnormalities, which type is most likely to be viable in humans?

Trisomy -Some trisomies are viable in humans, but they result in developmental abnormalities, such as Down syndrome (trisomy 21). Only humans with trisomies of the small chromosomes (13, 18, or 21) or the sex chromosomes survive past birth.

Which syndrome is characterized by the XO chromosome abnormality?

Turner Syndrome -Turner syndrome is characterized by a chromosome pattern of XO, or one X chromosome and no Y chromosome.

Mendel

When Mendel studied the inheritance of two characters in pea plants (such as seed color and seed shape), he found that alleles for different characters segregate independently. This means that genes are packaged into gametes in all possible allelic combinations, as long as each gamete has one allele for each gene. If genes are packaged into gametes in all possible combinations of alleles, then when you self-fertilize a plant heterozygous for two different traits (such as the YyRr plants in the example here), you see four different phenotypes in the F2 generation in a ratio of 9:3:3:1.

Part A - The inheritance of a skin condition in humans Consider the following family history: Bob has a genetic condition that affects his skin. Bob's wife, Eleanor, has normal skin. No one in Eleanor's family has ever had the skin condition. Bob and Eleanor have a large family. Of their eleven children, all six of their sons have normal skin, but all five of their daughters have the same skin condition as Bob. Based on Bob and Eleanor's family history, what inheritance pattern does the skin condition most likely follow?

X-linked dominant -If the skin condition is caused by an X-liked dominant allele, a father would pass the allele on to all of his daughters. In contrast, the father would not pass the allele on to any of his sons because the sons would receive the father's Y chromosomes, not his X chromosome.

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?

XNXn and XNY

diploid cell

a cell containing two sets of chromosomes, one set inherited from each parent.

SRY is best described in which of the following ways?

a gene region present on the Y chromosome that triggers male development

Turner Syndrome

a rare chromosomal disorder in females who have only one x chromosome. The syndrome is characterized by short stature, the lack of sexual development at puberty, and heart abnormalities.

What results if a fragment of a chromosome breaks off and then reattaches to the original chromosome at the same place but in the reverse direction?

an inversion

A nonreciprocal crossover causes which of the following products?

deletion and duplication

What phenomenon occurs when a particular allele will either be expressed or silenced, depending on whether it is inherited from a male or a female?

genomic imprinting -The sex of the parent transmitting a given chromosome can affect the chromosome's expression in the offspring.

triploid

having three sets of chromosome. In humans is lethal.

What can we observe in order to visualize Mendel's Law of Segregation?

homologous chromosomes separating during meiosis I -Homologous chromosomes each carry an allele or every gene. Those alleles may be the same or different, but they are segregated during meiosis 1 and distributed to each gamete.

In general, the frequency with which crossing over occurs between two linked genes depends on what?

how far apart they are on the chromosome -The farther apart two genes are, the greater the probability that a crossover will occur between them, and therefore the greater the recombination frequency.

Most polyploid plants arise as a result of _____.

hybridization -most polyploid plants are the results of the hybridization of two different parental species.

Nondisjunction Meiosis 2

if nondisjunction occurs in meiosis 2, both sister chromatids of a chromosome migrate to the same pole of the cell. Only one chromosome separates abnormally but this results in two abnormal cells. (n+1) (n-)