LIFE 120 Chapter 10: Meiosis and Sexual Life Cycles

In a male mammal, every cell that undergoes meiosis give rise to _______ sperm.

four One diploid parent cell gives rise to four haploid sex cells at the completion of the two meiotic divisions.

What is the result when a diploid cell undergoes meiosis?

four haploid cells The two cell divisions of meiosis, I and II, produce four haploid daughter cells, which are not genetically identical to the diploid parent cell.

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

liver cells Liver cells are somatic cells (body cells), and they contain the characteristic diploid chromosome number.

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

meiosis The two cell divisions of meiosis, I and II, produce four haploid daughter cells.

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.

The sexual cycle of the multicellular algal genus Fucus involves _________________.

mitosis, meiosis, and fertilization All multicellular organisms undergo mitosis, and all diploid, sexually reproducing organisms undergo meiosis and fertilization, which are complementary processes.

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

multicellular haploid stage (gametophyte), zygote, multicellular diploid stage (sporophyte), and spores In alternation of generations, zygotes give rise to multicellular, diploid sporophytes, and spores give rise to multicellular, haploid gametophytes.

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

multiplication of body cells that are genetically identical tot eh parent cell This is a function of mitosis in humans. It is mitosis that enables a multicellular adult to form from a fertilized egg and produces cells fro growth and tissue repair.

The synaptoemal complex _______________.

physically connects homologous chromosomes during prophase I The synaptonemal complex helps to line up homologous chromosomes gene by gene.

Synapsis occurs during _____________.

prophase I Synapsis is the pairing of homologous chromosomes during prophase I.

Crossing over occurs during ______________.

prophase I Crossing over resulting in genetic recombination occurs during this phase.

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

two haploid cells Each of these cells carries a haploid set of chromosomes, each consisting of two chromatids.

Which of the following occurs during anaphase II?

Sister chromatids separate and migrate toward opposite poles.

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

Synapsis of homologous pairs occurs. Synapsis of homologous chromosomes occurs at prophase I of meiosis I.

A karyotype is ____________________.

a display of all of an individual's chromosomes arranged in pairs Karyotypes, ordered displays of an individual's chromosomes, are useful in identifying chromosomal abnormalities.

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 union of haploid gametes at fertilization produces the zygote, or fertilized egg, which marks the beginning of the diploid phase of the life cycle.

Which, if any, of the following statements is true?

Haploid cells CANNOT divide by meiosis, diploid cells can divide by mitosis, diploid cells can divide by meiosis, and haploid cells can divide by mitosis. Diploid cells can divide by either mitosis or meiosis, but haploid cells can only divide by mitosis.

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 of obtaining a gamete in which all the chromosomes are paternal ones?

1/8 The chance of any one paternal chromosome ending up in a particular gamete is 1/2. so the chance that all three would be of paternal would be (1/2)^n, where n=3.

Ignoring crossover, how many kids 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.

How many pairs of autosomes do humans have?

22 Humans have 22 pairs of autosomes and one pair of sex chromosomes.

In humans, the haploid number of chromosomes is 23. Independent assortment has the possibility of producing ____________ different types of gametes.

2^23 For each gamete there are two possibilities for each chromosome (the paternal or the maternal chromosome), and there are 23 different chromosomes per gamete.

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

44 Haploid sex cells contain half as many chromosomes as diploid somatic cells.

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

5 Recall that meiosis is division of your gametes, which are haploid. Haploid sex cells contain half as many chromosomes as diploid somatic cells.

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. Asexual reproduction is cheaper than sexual reproduction but perpetuates the same combination of alleles in individuals over generations; thus, it does not provide the capacity for adaptation as do sexually reproducing organisms.

Which of the following occurs during anaphase I?

Homologs separate and migrate toward opposite poles, guided by the spindle apparatus.

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. Because each pair of homologous chromosomes is positioned independently in metaphase I, the first meiotic division results in the independent assortment of paternal and maternal chromosomes into daughter cells. In a case in which 2n=8, 16 combinations of chromosomes are possible for gametes.

Fertilization produces ___________________.

a diploid zygote Fertilization always involves the fusion of gametes and produces a diploid zygote.

Sister chromatids ________________.

are identical copies of each other formed during DNA synthesis Sister chromatids are identical and participate in both mitosis and meiosis.

A clone is the product of _______________________.

asexual reproduction and mitosis In asexual reproduction, an organism produces genetically identical progeny, or clones, by mitosis.

Regarding the role of cohesion protein in maintaining cohesion between sister chromatids, which of the following statements is FALSE? a. During meiosis I, cohesion holds sister chromatids together along their lengths as chiasmata form between homologs. b. During meiosis II, cohesion holds sister chromatids along their lengths as the second meiotic spindle forms. c. Cleavage of cohesions between sister chromatid arms at anaphase I allows homologs to separate. d. The first and second listed responses are false. e. The second and third responses are false.

b. During meiosis II, cohesion holds sister chromatids along their lengths as the second meiotic spindle forms. This statement is false. During meiosis II, cohesion holds the sister chromatids together at the centromeres prior to their separation at metaphase II.

Which of the following answers is NOT involved with or an outcome of crossing over? a. Chiasmata indicate where crossing over is occurring between homologs. b. The DNA in two non sister chromatids is broken by specific proteins at exact points. c. The random alignment of homologous pairs of chromosome at metaphase I d. formation of chromosomes containing paternal and maternal alleles e. All of the listed responded pertain to the process of crossing over.

c. The random alignment of homologous pairs of chromosome at metaphase I This process is not related to crossing over but is an outcome of independent assortment.

Regions of chromosomes where non sister chromatids cross over are called _____________.

chiasmata Chiasmata are regions where crossing over has occurred.

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 Unlike a gamete, a spore gives rise to a multicellular organism without fusing with another cell.

Which function makes meiosis lengthier and more complex than mitosis?

introducing genetic variation among the daughter cells; undergoing two rounds of cytokinesis; ensuring that each daughter cell gets a single, complete set of chromosomes; decreasing the chromosome number to haploid Meiosis involves two divisions that typically result in four daughter cells (instead of two). Each cell has half the number of chromosomes of the original parent cell and is, of course, not genetically identical to the parent cell.

The major contribution of sex to evolution is that _______________.

it increases genetic variation Sexual life cycles produce enormous genetic variation among offspring.

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

its cell have a single set of chromosomes Many fungi and some protists exist as haploid organisms, and plant and some algae also have a haploid stage (called a gametophyte) as part of the life cycle called alternation of generations. Also, human gametes (egg and sperm) are also haploid.

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

random fertilization, independent assortment, crossing over These three aspects of sexual reproduction increase genetic variation.

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 Although bdelloid rotifers are incapable of sexual reproduction, they can carry out a form of "horizontal gene transfer" in which they take up DNA from the environment and incorporate it into their genome. This adaptation demonstrates that asexually reproducing animals are not limited to mutation alone in generating genetic diversity in a population.

How many genes are present in the human genome?

tens of thousands Each chromosome has hundreds or thousands of genes; the entire human genome has on the order of 20,000 to 25,000 genes.

What is a locus?

the specific location of a gene along the length of a chromosome The location of a gene within the genome, including the identity of the particular chromosome that it maps to and its specific position on the chromosome, is called it locus.

Sexual and asexual reproduction are alike in that _________________.

they can both occur in multicellular organisms Examples of both sexual and asexual reproduction have been observed in multicellular organisms.

What is the function of meiosis?

to make cells with a haploid (half that of the parents) number of chromosomes The two cell divisions of meiosis, I and II, produce four haploid daughter cells, which are not genetically identical to the diploid parent cell.

Somatic cells in human contain _______________ set(s) of chromosomes and are therefore termed ______________.

two ... diploid Somatic cells (body cells) in interphase contain the characteristic diploid chromosome number. Recall that it is your sex cells (gametes) that are haploid.