Mastering Bio Chapter 13

How many double-helical DNA molecules will be present in the sperm and egg cells of dogs that are diploid animals that contain 78 replicated chromosomes in each cell that enters meiosis?

39

The domestic dog has a diploid number (2n) of 78; 76 of the chromosomes are autosomes and 2 are sex chromosomes (X and Y). A karyotype taken from a dog's mature egg cell would have how many chromosomes?

39

Somatic cells from an individual with Down syndrome (trisomy 21) have ______ copies of the genes on chromosome 20 and ______ copies of the genes on chromosome 21.

two, three

Which processes lead to most genetic variation in sexually reproducing organisms?

- random fertilization - independent assortment of chromosomes in meiosis - crossing over

Meiosis results in independent assortment of maternal and paternal chromosomes. If 2n = 6 for a given organism and there is no crossing over, what is the chance that a gamete produced by this diploid organism will receive only paternal chromosomes?

1/8

If a cell has 24 chromosomes, how many chromosomes would each of its four daughter cells have after meiosis?

12

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

When can nondisjunction occur? Choose the best answer.

All three answers are correct.

What is a nondisjunction?

An error in cell division that causes homologous chromosomes or sister chromatids to move to the same side of the dividing cell

During _____ sister chromatids separate.

Anaphase II

If you followed a woman's cells through meiosis, at what stage of meiosis would the amount of DNA in one of these cells be equal to the amount of DNA in one of her G1 phase (before DNA replication) kidney cells?

At the end of meiosis I

Which of these gametes contains one or more recombinant chromosomes?

B and C

Which of these gametes contain one or more recombinant chromosomes?

B, C, F, G

What are bivalents and where are they found in the process of meiosis?

Bivalents are formed by the pairing of the replicated homologous chromosomes that we can observe during prophase I and metaphase I of meiosis I.

Which of these cells is (are) haploid?

C and D

Which structure is directly correlated with the production of genetic variability in the daughter cells produced during meiosis?

Chiasma

The parent cell that enters meiosis is diploid, whereas the four daughter cells that result are haploid. Which statement correctly describes how cellular DNA content and ploidy levels change during meiosis I and meiosis II?

DNA content is halved in both meiosis I and meiosis II. Ploidy level changes from diploid to haploid in meiosis I, and remains haploid in meiosis II.

Crossing over prevents homologous chromosomes from separating during meiosis I.

False

Homologous chromosomes form pairs during both mitosis and meiosis.

False

The chromosomes are replicated

False

The total number of chromosomes is reduced by half during both mitosis and meiosis

False

True or false? A haploid organism has one pair of homologous chromosomes.

False

Which statement about the difference between homologous chromosomes and sister chromatids is correct?

Homologous chromosomes contain the same genes but often different alleles. Sister chromatids contain the same genes and the same alleles.

A key difference between mitosis and meiosis is

Homologs pair up and crossing over happens during meiosis I but does not happen in mitosis

Which of the following statements about meiosis and mitosis is true?

Meiosis II is similar to mitosis in that sister chromatids of each chromosome separate.

What is the composition of a tetrad at the beginning of prophase I?

One pair of homologous chromosomes

Synapsis occurs during _____.

Prophase I

Compare the two cells shown in this image. Which of the following statements is correct?

The number of chromosomes in both cells is the same, but the bottom cell contains twice the amount of DNA as the top cell.

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

Trisomy

As a result of crossing over, sister chromatids are no longer identical to each other.

True

Chiasma form during meiosis I but not during mitosis.

True

Crossing over occurs at the ends of chromosomes, rather than near the centromeres.

True

Each chromosome contains one long molecule of double-stranded DNA and proteins.

True

For crossing over to occur, homologous chromosomes must align precisely early in prophase I so that nonsister chromatids can exchange corresponding segments of DNA.

True

The bands on the chromosomes represent certain genes

True

The sister chromatids of replicated chromosomes separate during both mitosis and meiosis II.

True

There are five different lengths of chromosomes in this cell.

True

Which syndrome is characterized by the XO chromosome abnormality?

Turner syndrome

Homologous chromosomes migrate to opposite poles during _____.

anaphase I

What are homologous chromosomes?

chromosomes that are similar in their size, shape, and gene content

Meiosis II typically produces _____ cells, each of which is _____.

four, haploid

What is the ploidy of this cell model?

haploid

Meiotic nondisjunction could be a result of __________.

incorrect segregation of homologous chromosomes during meiosis I

Human gametes are produced by _____.

meiosis

Nondisjunction that leads to problems in offspring can occur in _____.

meiosis I and II

Homologous pairs of chromosomes are lined up independently of other such pairs during _____.

metaphase I

During _____ chromosomes align single file along the equator of a haploid cell.

metaphase II

What stage of cell division does this image show?

metaphase of mitosis

What is the ploidy of this cell model?

n=6

Crossing over, resulting in an increase in genetic variation, occurs between _____.

nonsister chromatids of homologous chromosomes

During _____ a spindle forms in a haploid cell.

prophase II

At the end of _____ and cytokinesis, haploid cells contain chromosomes that each consist of two sister chromatids.

telophase I

At the end of _____ and cytokinesis there are four haploid cells.

telophase II

What is an outcome of genetic recombination?

the new combination of maternal and paternal chromosome segments that results when homologs cross over

What is the ploidy of this cell model?

triploid

Meiosis I produces _____ cells, each of which is _____

two, haploid

Normal human gametes carry _____ chromosomes.

23

What is the ploidy of organisms that have two sets of chromosomes?

2n

What is the ploidy of this cell model?

2n=6

In human gamete production there is an average of _____ crossover events per chromosome pair.

2-3

A diploid organism whose somatic (nonsex) cells each contain 32 chromosomes produces gametes containing _____ chromosomes.

16

What information can not be obtained from an individual's karyotype?

The sequence of bases of a particular gene

If crossing over did not occur, which of the following statements about meiosis would be true? Select all that apply.

There would be less genetic variation among gametes.

This cell is 2n = 10

True

This cell is diploid

True