Biology Mitosis

Pairing of homologous chromosomes is followed by _________, the exchange of genetic material between nonsister chromatids of homologous chromosomes.

crossing over

Mitosis is followed by cytokinesis, when the _________ splits to form two separate daughter cells.

cytoplasm

Once meiosis I is completed, cells are _______

haploid

If a diploid dog cell enters meiosis, how many chromosomes and chromatids will be present in each daughter cell at the end of meiosis II?

39 chromosomes and 39 chromatids

In which mitotic phase are the sister chromatids separated and pulled to opposite poles?

anaphase

Normal human gametes carry _____ chromosomes.

23

During prophase, microtubules grow out from the centrosomes, initiating formation of the?

mitotic spindle

In organisms that reproduce sexually, the processes of DNA replication, the precise pairing of homologs during crossing over, chromosome alignment and separation in meiosis I and II, and fertilization ensure that traits pass from one generation to the next. Unlike with asexual reproduction, offspring of sexual reproduction are genetically different from each other and from both of their parents. Mechanisms that contribute to genetic variation include:

1. errors (mutations) that occur during DNA replication 2. the production of recombinant chromosomes due to crossing over 3. the independent assortment of homologous chromosomes in meiosis I 4. the separation of sister chromatids (which are no longer identical due to crossing over) in meiosis II 5. the random fusion of male and female gametes during fertilization

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

12. Meiosis is a reduction division that reduces the number of chromosomes passed on to daughter cells by one-half.

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

16 is half of 32

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

2-3. These crossover events increase the genetic variation among gametes.

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

2n. An organism that has two sets of chromosomes has a ploidy of 2n.

Which of these individuals is a homozygous genotype? Gg Aa AA aG AG

AA When both of the alleles of a given gene pair are the same, the individual is homozygous for that gene.

Every few years a giant axe chops off the head of every person who is over 6 feet tall. How will this affect the human population?

Alleles that promote "tallness" will decrease in frequency. A reduction in "tallness" alleles is the change expected as a result of this type of selection.

Meiosis I produces _____ cells, each of which is _____.

At the end of meiosis I there are two haploid cells.

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

At the end of meiosis II there are typically 4 haploid cells.

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

At the end of telophase I and cytokinesis, there are two haploid cells with chromosomes that consist of two sister chromatids each.

How is plant cell cytokinesis different from animal cell cytokinesis?

Plant cells deposit vesicles containing cell-wall building blocks on the metaphase plate; animal cells form a cleavage furrow

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

Chiasma. The chiasma is an X-shaped structure formed from the crossing over of homologous chromosomes, which can then exchange segments at the crossover sites.

During which substage of mitosis do sister chromatids break apart and start moving to opposite poles of the cell?

Chromatids are pulled to opposite poles of the cell during anaphase, the fourth substage of mitosis.

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. During anaphase of both meiosis I and meiosis II, the DNA content (number of copies of chromosomes) in a cell is halved. However, the ploidy level changes only when the number of unique chromosome sets in the cell changes. This occurs only in meiosis I (where separation of homologous chromosomes decreases the ploidy level from 2n to n and produces daughter cells with a single chromosome set).

True or false? Mitosis takes place during M phase, which is the longest phase of the cell cycle.

False, Mitosis does indeed take place during M phase, but M phase is the shortest phase of the cell cycle.

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

False. A haploid organism only has one set of chromosomes, so it has no homologous chromosomes.

Which of the following statements about meiosis and mitosis is true? A. In meiosis II and mitosis, a diploid cell divides. B. In mitosis and meiosis I, homologous chromosomes move independently of each other. C. Each daughter cell produced during meiosis and mitosis is genetically identical to the parent cell. D. Meiosis II is similar to mitosis in that sister chromatids of each chromosome separate.

Meiosis II is similar to mitosis in that sister chromatids of each chromosome separate. Both meiosis II and mitosis are cell divisions involving the separation of sister chromatids.

Human gametes are produced by _____.

Meiosis produces haploid gametes from a diploid parental cell.

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

Metaphase II is essentially the same as mitotic metaphase except that the cell is haploid.

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

One pair of homologous chromosomes. One chromosome in a tetrad is paternally inherited, while the other is maternally inherited. Each chromosome consists of two chromatids.

Which term describes two recently replicated DNA strands that are joined together just before cell division?

Sister chromatids are the two strands of a recently replicated chromosome that will be split apart during cell division.

To which part of the centromere do mitotic spindle fibers attach during prometaphase?

The kinetochore is the region of the centromere on the sister chromatid to which the mitotic spindle attaches.

Centromeres divide and sister chromatids become full-fledged chromosomes during _____.

anaphase

Which stage of mitosis is characterized by the disintegration of mitotic spindles and the formation of two new nuclear membranes?

The mitotic spindles disintegrate and a nuclear envelope begins to form around each set of chromosomes during telophase, the last substage of mitosis.

Which event does not take place before the start of mitosis? A. The parent cell grows. B. The nuclear envelope disintegrates. C. Organelles proliferate. D. DNA is replicated.

The nuclear envelope disintegrates.

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

The sequence of bases of a particular gene. Karyotypes only give information about the chromosomes in an individual.

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.

During prophase a homologous pair of chromosomes consists of _____.

Two (2) chromosomes and Four (4) Chromatids

Prophase

cohesions join sister chromatids of duplicated chromosome, tubulins assemble into spindle microtubules

Homologous chromosomes migrate to opposite poles during _____.

anaphase I During anaphase I sister chromatids remain attached at their centromeres, and homologous chromosomes move to opposite poles.

During _____ sister chromatids separate.

anaphase II

An advantage of sexual reproduction is hypothesized to be ___________.

avoiding the transmission of harmful alleles to offspring

Anaphase begins when the two ________ of each chromosome come apart, separating the sister chromatids. Once separate, each sister chromatid is considered a full-fledged daughter chromosome. Motor proteins of the kinetochores "walk" the daughter chromosomes along the spindle microtubules toward opposite poles, and the microtubules shorten. At the same time, the spindle microtubules not attached to chromosomes _______, pushing the two poles farther apart and elongating the cell.

centromeres, lengthen

The cytoplasm of a cell in late interphase contains two _________, each of which may contain a pair of _______.

centrosomes, centrioles

In the nucleus of a cell in late interphase, the chromosomes have been replicated during S phase, but are still dispersed in the form of _______. One or more ______ are present.

chromatin, nucleoli

During prophase, the nucleoli disappear and chromatin fibers coil up to become discrete ____________. Each chromosome consists of two identical sister chromatids, joined at the _______.

chromosomes, centromere

In animal cells, cytokinesis begins with the formation of a ________ furrow. At the site of the furrow, a ring of microfilaments contracts, much like the pulling of drawstrings. The cell is pinched in two, creating two identical daughter cells.

cleavage

anaphase

cohesions break down, kinetochores move toward poles of cell

During telophase, the nonkineochore microtubules _________

disassemble

All the genes in a population are that population's _____.

gene pool. All the alleles of all the genes of a population make up a gene pool.

The ease with which humans travel across the globe is likely to increase _____.

gene flow. When people travel or migrate, they take their alleles with them.

metaphase

kinetochores are motionless in relation to poles of cell

Modern travel along with migration reduces the probability of _____ having an effect on the evolution of humans.

genetic drift. Modern travel and migration decreases the chances of there being a small, isolated population.

Nucleoli are present during _____.

interphase

During prometaphase, the nuclear envelope breaks into fragments. Some of the spindle fibers reach the chromosomes and attach to _____________, structures made of proteins and specific sections of DNA at the centromeres. ________________ microtubules overlap with those coming from the opposite pole.

kinetochores, Nonkinetochore

During prophase, the microtubules of the mitotic spindle ________

lengthen

During anaphase, the nonkinetochore microtubules ______ and move past each other, and the kinetochore microtubules _______.

lengthen, shorten

During which stage of mitosis are chromosomes lined up in the center of the cell?

metaphase

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

metaphase I

prometaphase

microtubules attach to kinetochores

Cell division consists of two processes: ________ and ________

mitosis, and cytokinesis

At metaphase, the ____________ is fully formed, and the microtubules attached to kinetochores move the _______ to the metaphase plate, an imaginary plane equidistant from the poles.

mitotic spindle, chromosomes

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

nonsister chromatids of homologous chromosomes. This process produces chromosomes containing genes inherited from both parents.

During telophase, ________________ form around the identical sets of chromosomes at the two poles of the cell. The chromosomes uncoil and nucleoli appear in the two new nuclei. Meanwhile, cytokinesis begins, splitting the __________ and separating the two daughter cells.

nuclear envelopes, cytoplasm

Spindle fibers attach to kinetochores during _____.

prometaphase

Chromosomes become visible during _____.

prophase

Crossing over occurs during ________ when homologous chromosomes loosely pair up along their lengths. Crossing over occurs only between nonsister chromatids within a homologous pair of chromosomes, not between the sister chromatids of a replicated chromosome. Only segments near the ends of the chromatids, not segments nearest the centromeres, can exchange DNA.

prophase I

Synapsis occurs during _____.

prophase I

Meiosis I, consists of what stages?

prophase I, metaphase I, anaphase I, and telophase I (followed by cytokinesis)

During _____ a spindle forms in a haploid cell.

prophase II

Meiosis II, consists of what stages?

prophase II, metaphase II, anaphase II, and telophase II (followed by cytokinesis)

telophase

spindle microtubules disassemble

Cytokinesis often, but not always, accompanies _____.

telophase

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

telophase II

Genetic drift is a process based on _____.

the role of chance. Genetic drift requires a small sample size.

A mutation occurs when _____.

there is a change in the DNA sequence of a gene

Meiosis is mechanistically similar to mitosis in many ways, although it involves ____ sequential nuclear and cellular divisions.

two

In plant cells, cytokinesis begins when vesicles containing cell-wall material collect in the middle of the cell. The vesicles fuse, forming a large sac called the cell plate. The cell plate grows outward until its membrane fuses with the plasma membrane, separating the two daughter cells. The cell plate's contents join the parental cell wall. The result is?

two daughter cells, each bounded by its own continuous plasma membrane and cell wall.