Chapter 13 Biology

For what purpose(s) might a karyotype be prepared?

1. for prenatal screening, to determine if a fetus has the correct number of chromosomes 2. to determine whether a fetus is male or female 3. to detect the possible presence of chromosomal abnormalities such as deletions, inversions, or translocations

In a diploid set of chromosomes, one member of each pair of homologous chromosomes is derived from the father (paternal), and the other comes from the mother (maternal). If 2n = 6, what is the probability that a particular gamete will contain only paternal chromosomes?

1/8 (2n=6, n=3, 2^n=2^3=8)

Ignoring crossover events, how many kinds of gametes can be produced by an organism with a diploid number of 8?

16 (The number of combinations possible when chromosomes assort independently into gametes during meiosis is 2^n, where n is the haploid number of chromosomes.)

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

2-3

How many pairs of autosomes do humans have?

22

What number and types of chromosomes are found in a human gametic cell?

22 autosomes and 1 sex chromosome

If the DNA content of a diploid cell in the G1 phase of the cell cycle is x, then the DNA content of the same cell at metaphase of meiosis I would be

2x

An organism has a haploid chromosome number n = 4. How many tetrads will form during meiosis?

4 (Because of the synapsis of homologous chromosomes, the number of tetrads in meiosis I will be the same as the haploid number of chromosomes.)

The egg (ovum) of a rabbit contains 22 chromosomes. How many chromosomes are in the somatic (body) cells of a rabbit?

44

How many chromosomes does a human somatic cell have?

46

In a diploid cell containing 10 chromosomes, meiosis results in the formation of daughter cells containing __________ chromosomes.

5

Which of the following statements is most accurate?

All of the listed responses are correct. -Diploid cells can divide by mitosis. -Diploid cells can divide by meiosis. -Haploid cells can divide by mitosis. -Haploid cells cannot divide by meiosis.

Which function makes meiosis lengthier and more complex than mitosis?

All of the listed responses are correct. -Introducing genetic variation among the daughter cells -Decreasing the chromosome number to haploid -Ensuring that each daughter cell gets a single, complete set of chromosomes -Undergoing two rounds of cytokinesis

Which of the following is part of the life cycle called alternation of generations?

All of the listed responses are correct. -Spores -Zygote -Multicellular haploid stage (gametophyte) -Multicellular diploid stage (sporophyte)

Which of the following statements reflects an advantage that sexual reproduction likely provides over asexual reproduction?

Although energetically more costly than asexual reproduction, sexual reproduction leads to different combinations of alleles that could provide adaptability in a changing environment.

Which of the following results when homologous chromosomes cross over in meiosis?

Corresponding segments of non-sister chromatids are exchanged.

Which of the following statements describes one characteristic of each chromosome in a cell during the entire process of meiosis I?

Each chromosome consists of two sister chromatids joined by a centromere.

Which of the following statements is true of a species that has a chromosome number of 2n = 16?

Each diploid cell has eight homologous pairs of chromosomes.

List other possible combinations of these alleles in this individual's gametes.

FFHH ("freckles" and "black hair") + ffhh ("no freckles" and "blond hair")

What is the typical result when a diploid cell has completed meiosis?

Four haploid cells

Which of the following occurs in meiosis but not mitosis?

Homologous chromosomes separate

Which of the following occurs during anaphase I?

Homologs separate and migrate toward opposite poles.

For the following question, match the key event of meiosis with the stages listed below. I.Prophase I II.Metaphase I III.Anaphase I IV.Telophase I V.Prophase II VI.Metaphase II VII.Anaphase II VIII.Telophase II Homologous chromosomes are aligned at the middle of the spindle.

II.Metaphase I

Which of the following statements about reproduction is correct?

In sexual reproduction, individuals transmit half of their nuclear genes to each of their offspring.

Which of the following answers is neither involved with crossing over nor an outcome of crossing over?

Independent assortment results from the random alignment of homologous pairs of chromosomes at metaphase I.

A particular organism has 46 chromosomes in its karyotype. Which of the following statements is correct regarding this organism?

It produces gametes with 23 chromosomes.

Which of the following results in cells that contain half the parental chromosome number?

Meiosis

Which of the following is a function of mitosis in humans?

Multiplication of body cells

Which of the following contributes to genetic variation in sexually reproducing species?

Random fertilization, independent assortment, crossing over

How does natural selection apply to sexual reproduction as opposed to asexual reproduction?

Sexual reproduction results in new gene combinations, some of which will have increased reproductive fitness.

Which of the following occurs during anaphase II?

Sister chromatids separate and migrate toward opposite poles.

Two different species of protists living in a tide pool. Species A reproduces both sexually and asexually, and Species B reproduce only asexually. The pool gradually becomes infested with disease-causing viruses. Which species are more likely to survive in the changing environment?

Species A only

Which event occurs only during prophase I of the first meiotic division?

Synapsis of homologous pairs occurs.

How do cells at the completion of meiosis compare with cells that are in prophase of meiosis I?

The cells have half the number of chromosomes and one-fourth the amount of DNA.

What is a locus?

The precise location of a gene on a chromosome

Assume that an organism exists in which crossing over does not occur, but that all other processes associated with meiosis occur normally. Consider how the absence of crossing over would affect the outcome of meiosis. 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.

The diploid number of chromosomes in a certain animal is 8 (2n = 8). How do the four pairs of homologous chromosomes align and separate during meiosis?

They align and assort independently to form any of 16 different combinations.

Which of the following statements about homologous chromosomes is correct?

They have genes for the same traits at the same loci.

What is the function of meiosis?

To make cells with a haploid (half that of the parents) number of chromosomes

The diagram represents just a few of the chromosomes of a meiotic cell in a certain person. Assume that the freckles gene is located at the locus marked FF, and the hair-color gene is located at the locus marked HH, both on the long chromosome. The individual from whom this cell was taken has inherited different alleles for each gene ("freckles" and "black hair" from one parent, and "no freckles" and "blond hair" from the other). Predict allele combinations in the gametes resulting from this meiotic event. (It will help if you draw out the rest of meiosis and label the alleles by name.)

Two cells will be obtained after meiosis I. The first cell will be FfHH and will get the "freckles" and "black hair" + "no freckles" and "black hair" alleles, and the second will be Ffhh and will get the "no freckles" and "blond hair" + "freckles" and "blond hair" alleles.

The Cavendish banana, the world's most popular fruit, is currently threatened by extinction due to a fungus. This banana variety is "triploid" (3n3n, with three sets of chromosomes) and can only reproduce through cloning by cultivators. Given what you know about meiosis, choose how the banana's triploid number accounts for its inability to form normal gametes.

With three sets of chromosomes, there is no way for the sets to be separated equally to gametes during meiosis, and so seeds cannot form.

Fertilization produces __________.

a diploid zygote

A karyotype is __________.

a photograph of all the chromosomes in a single cell from an individual

A human cell containing 22 autosomes and a Y chromosome is

a sperm

During this process, crossing over and independent assortment of chromosomes result in many gametes with novel combinations of ___________.

alleles

Which of the following processes will most likely produce a human zygote with 45 chromosomes?

an error during anaphase II while the sperm was produced

During which of the following phases of meiosis do homologous chromosomes separate?

anaphase I

Sister chromatids __________.

are identical copies of each other formed through DNA synthesis

Nearly all life cycles have both haploid and diploid phases. Usually, the transition from haploid to diploid takes place __________.

at fertilization, when gametes fuse

The offspring inherits genes from ____________ and exhibits traits in new combinations.

both parents

Regions of chromosomes where nonsister chromatids cross over are called __________.

chiasmata

Cytokinesis is the __________.

division of the cytoplasm to create two cells

Heritable variation is required for which of the following?

evolution

A life cycle in which the only multicellular form is haploid is most typical of __________.

fungi

Spores and gametes are different in that __________.

gametes can fuse to form a zygote, but spores can develop into independent organisms without first forming a zygote

Any pair of _________ (e.g. egg and sperm), each containing chromosomes from __________, can fuse during fertilization to make a ___________ cell.

gametes; one parent; diploid

Meiosis in each parent generates _________ gametes with a ___________ set of chromosomes.

haploid; single

Which of the following pairs of processes make the greatest contribution to genetic diversity between generations of a diploid insect?

independent assortment and random fertilization

The major contribution of sex to evolution is that __________.

it provides a method to increase genetic variation

When we say that an organism is haploid, we mean that __________.

its cells have a single set of chromosomes

Humans have 46 chromosomes. This number of chromosomes will be found in __________.

liver cells

In a human karyotype, chromosomes are arranged in 23 pairs. If one of the autosomal pairs is examined, which of the following characteristics will the two chromosomes of the pair have in common?

loci and staining pattern

Homologous chromosomes move toward opposite poles of a dividing cell during

meiosis I

The two homologs of a pair move toward opposite poles of a dividing cell during

meiosis I

In sexually reproducing species, the chromosome number remains stable over time because __________ and __________ always alternate.

meiosis; fertilization (Meiosis reduces the number of chromosomes by half, and fertilization restores the number to the diploid state.)

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

metaphase I

Asexual reproduction occurs during which of the following processes?

mitosis

The sexual cycle of the diploid, multicellular algal genus Fucus involves __________.

mitosis, meiosis, and fertilization

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

nonsister chromatids of homologous chromosomes

The synaptonemal complex __________.

physically connects homologous chromosomes during prophase I

Crossing over occurs during __________.

prophase I

Synapsis occurs during __________.

prophase I of meiosis (Synapsis is the pairing of homologous chromosomes during prophase I.)

Although __________ is nearly universal among animals, bdelloid rotifers __________.

sexual reproduction; reproduce asexually but can increase genetic variation present in a population by means of the uptake of DNA from other rotifers

Meiosis II is similar to mitosis in that

sister chromatids separate during anaphase.

How many genes are present in the human genome?

tens of thousands

Which of the following phrases defines the term genome?

the complete set of an organism's genes and other DNA sequences

Independent assortment of chromosomes is a result of which of the following processes?

the random way each pair of homologous chromosomes lines up at the metaphase plate during meiosis I

Sexual and asexual reproduction are alike in that __________.

they can both occur in multicellular organisms

This random fertilization further augments the number of different possible combinations of ___________ that can be obtained.

traits

Somatic cells of roundworms have four individual chromosomes per cell. How many chromosomes would you expect to find in an ovum from a roundworm?

two

At the end of telophase I of meiosis and the first cytokinesis, there are __________.

two haploid cells

Somatic cells in humans contain __________ set(s) of chromosomes and are therefore termed __________.

two; diploid

Question 5:If we continued to follow the cell lineage from question 4, then the DNA content of a single cell at metaphase of meiosis II would be

x