What is the chief evolutionary advantage of sexual reproduction over asexual reproduction?
It produces genetic variation among offspring
✓
It allows a population to grow faster
It removes the need to find a mate
It produces offspring identical to the parent
Correct Answer
It produces genetic variation among offspring
By combining genes from two parents and shuffling them during meiosis, sexual reproduction produces genetically varied offspring, which helps a population adapt to changing conditions. It allows a population to grow faster is wrong because asexual populations can grow faster. It removes the need to find a mate describes asexual reproduction. It produces offspring identical to the parent also describes asexual reproduction.
Category: Sexual Reproduction
Question 2
The Red Queen hypothesis explains the persistence of sexual reproduction by pointing to which factor?
The energy saved by not searching for mates
Coevolution with predators, prey, parasites and hosts
✓
The faster growth of all-female populations
The protection of genes from new mutations
Correct Answer
Coevolution with predators, prey, parasites and hosts
The Red Queen hypothesis holds that species must keep adapting just to keep up with the other species they interact with, and the variation from sexual reproduction makes that possible. The energy saved by not searching for mates is an advantage of asexual reproduction. The faster growth of all-female populations is also an advantage of asexual reproduction. The protection of genes from new mutations is not what sex does; it shuffles mutations into new combinations.
Category: Sexual Reproduction
Question 3
In a diploid-dominant life cycle like that of humans, which cells are the only haploid cells?
Spores
Somatic cells
Gametes
✓
Zygotes
Correct Answer
Gametes
In diploid-dominant life cycles, found in nearly all animals, the body is diploid and only the eggs and sperm are haploid. Spores are haploid cells of fungi, plants and some algae, not of humans. Somatic cells are the diploid body cells. Zygotes are diploid cells formed when an egg and a sperm fuse.
Category: Life Cycles
Question 4
Which of these groups typically has a haploid-dominant life cycle, in which the zygote is the only diploid stage?
Mammals
Flowering plants
Insects
Fungi
✓
Correct Answer
Fungi
In a haploid-dominant life cycle the multicellular body is haploid, and the diploid zygote immediately undergoes meiosis to make haploid spores; fungi and some algae follow this pattern. Mammals are diploid-dominant. Flowering plants have alternation of generations. Insects, like other animals, are diploid-dominant.
Category: Life Cycles
Question 5
In plants with alternation of generations, what process does the haploid multicellular gametophyte use to make eggs and sperm?
Mitosis
✓
Meiosis
Binary fission
Crossing over
Correct Answer
Mitosis
Because the gametophyte is already haploid, it makes eggs and sperm by mitosis, which keeps the chromosome number the same. Meiosis happens in the sporophyte, where it makes haploid spores. Binary fission is how prokaryotes divide. Crossing over is an event within meiosis, not a way of making cells.
Category: Life Cycles
Question 6
In alternation of generations, which multicellular stage produces haploid spores by meiosis?
Gametophyte
Sporophyte
✓
Zygote
Gamete
Correct Answer
Sporophyte
The diploid sporophyte grows from the zygote by mitosis, and some of its cells undergo meiosis to form haploid spores that grow into gametophytes. The gametophyte is haploid and makes gametes by mitosis. The zygote is a single diploid cell, not a multicellular stage. A gamete is a single haploid cell that fuses at fertilization.
Category: Life Cycles
Question 7
During which phase of meiosis does crossing over between homologous chromosomes take place?
Metaphase I
Anaphase II
Prophase I
✓
Prophase II
Correct Answer
Prophase I
Crossing over happens in prophase I, while homologous chromosomes are tightly paired. Metaphase I is when the paired homologs line up at the center of the cell. Anaphase II is when sister chromatids separate. Prophase II involves chromosomes that are no longer paired with their homologs, so no crossing over occurs.
Category: Meiosis I
Question 8
What is the term for the tight, gene-by-gene pairing of homologous chromosomes early in the first meiotic division?
Cytokinesis
Interkinesis
Nondisjunction
Synapsis
✓
Correct Answer
Synapsis
Synapsis is the close pairing of homologous chromosomes, aligned so their matching genes sit side by side, which sets up crossing over. Cytokinesis is the division of the cytoplasm. Interkinesis is the brief pause some species show between the two meiotic divisions. Nondisjunction is the failure of chromosomes to separate correctly.
Category: Meiosis I
Question 9
The visible points where non-sister chromatids of paired homologs have exchanged segments are called what?
Chiasmata
✓
Centromeres
Kinetochores
Centrosomes
Correct Answer
Chiasmata
Chiasmata (singular chiasma) mark the sites of crossing over and hold homologs together until anaphase I. Centromeres are the regions that join sister chromatids. Kinetochores are protein structures where spindle microtubules attach. Centrosomes are organelles that organize the spindle in animal cells.
Category: Meiosis I
Question 10
A cell has 3 pairs of homologous chromosomes. Ignoring crossing over, how many different chromosome combinations can independent assortment place in the resulting cells?
6
8
✓
9
3
Correct Answer
8
Each homologous pair lines up independently, so the number of combinations is 2 raised to the number of pairs: 2 x 2 x 2 = 8. The value 6 comes from multiplying 2 by 3 instead of raising 2 to the third power. The value 9 comes from squaring 3. The value 3 is just the number of pairs.
Category: Meiosis I
Question 11
At the end of the first meiotic division, each daughter cell is haploid, but each of its chromosomes still consists of what?
A single chromatid
Four chromatids
Two sister chromatids
✓
A pair of homologs
Correct Answer
Two sister chromatids
Meiosis I separates homologous chromosomes, but sister chromatids stay joined at the centromere until meiosis II, so each chromosome is still duplicated. A single chromatid describes chromosomes only after meiosis II. Four chromatids describes a tetrad during prophase I. A pair of homologs is what was separated in meiosis I.
Category: Meiosis I
Question 12
Which division of meiosis is called the reduction division because it cuts the number of chromosome sets from two to one?
Meiosis II
Interkinesis
Telophase II
Meiosis I
✓
Correct Answer
Meiosis I
Meiosis I separates homologous chromosomes, so each daughter cell receives one set instead of two. Meiosis II separates sister chromatids and does not change the number of sets. Interkinesis is a pause between divisions, not a division. Telophase II is a stage at the end of meiosis II.
Category: Meiosis II
Question 13
Meiosis II most closely resembles which process?
Mitosis of a haploid cell
✓
Mitosis of a diploid cell
Binary fission of a bacterium
Fusion of an egg and a sperm
Correct Answer
Mitosis of a haploid cell
In meiosis II, the sister chromatids of each chromosome separate, just as in mitosis, but the cells dividing contain only one set of chromosomes. Mitosis of a diploid cell is wrong because cells entering meiosis II are already haploid. Binary fission of a bacterium is prokaryotic cell division. Fusion of an egg and a sperm is fertilization.
Category: Meiosis II
Question 14
A diploid cell completes meiosis, including cytokinesis. What does it produce?
Two diploid cells
Four haploid cells
✓
Four diploid cells
Two haploid cells
Correct Answer
Four haploid cells
Meiosis involves one round of DNA replication followed by two divisions, giving four cells that each have one set of chromosomes. Two diploid cells is the result of mitosis in a diploid cell. Four diploid cells would require no reduction in chromosome sets. Two haploid cells is the result after meiosis I only.
Category: Meiosis Versus Mitosis
Question 15
Which event is unique to meiosis?
Replication of DNA in S phase
Separation of sister chromatids
Formation of tetrads
✓
Breakdown of the nuclear envelope
Correct Answer
Formation of tetrads
Homologous chromosomes pair to form tetrads only in prophase I of meiosis, which allows crossing over. Replication of DNA in S phase precedes both mitosis and meiosis. Separation of sister chromatids happens in mitosis and in meiosis II. Breakdown of the nuclear envelope happens in both processes.
Category: Meiosis Versus Mitosis
Question 16
What is the term for the failure of homologous chromosomes or sister chromatids to separate properly during meiosis?
Translocation
Inversion
Polyploidy
Nondisjunction
✓
Correct Answer
Nondisjunction
Nondisjunction leaves one gamete with an extra copy of a chromosome and another with a missing copy. Translocation is the movement of a chromosome segment to a nonhomologous chromosome. Inversion is a segment that flips and reinserts. Polyploidy is having extra complete sets of chromosomes.
Category: Chromosome Errors
Question 17
Down syndrome results from which chromosomal condition?
Trisomy 21
✓
Monosomy 21
Trisomy 18
Deletion on chromosome 5
Correct Answer
Trisomy 21
Down syndrome is caused by a third copy of chromosome 21, the most common trisomy among live-born humans. Monosomy 21 would mean a missing copy, not an extra one. Trisomy 18 is a different, more severe condition. A deletion on chromosome 5 causes cri-du-chat syndrome.
Category: Chromosome Errors
Question 18
A person with the sex chromosomes XXY has which condition?
Turner syndrome
Klinefelter syndrome
✓
Down syndrome
Cri-du-chat syndrome
Correct Answer
Klinefelter syndrome
Klinefelter syndrome affects males with an extra X chromosome (XXY) and can cause small testes, breast enlargement and reduced body hair. Turner syndrome affects females with a single X chromosome. Down syndrome involves an extra chromosome 21, an autosome. Cri-du-chat syndrome results from a deletion on chromosome 5.
Category: Sex Chromosomes
Question 19
What is the condensed, inactivated X chromosome in the cell of a female mammal called?
Chiasma
Kinetochore
Barr body
✓
Centromere
Correct Answer
Barr body
Early in female embryonic development, one X chromosome in each cell condenses into a Barr body and its genes are silenced, so females and males have similar doses of X-linked genes. A chiasma is a site of crossing over. A kinetochore is where spindle microtubules attach to a chromosome. A centromere is the region joining sister chromatids.
Category: Sex Chromosomes
Question 20
In which chromosomal rearrangement does a segment break off one chromosome and attach to a nonhomologous chromosome?
Inversion
Duplication
Deletion
Translocation
✓
Correct Answer
Translocation
A translocation moves a chromosome segment to a nonhomologous chromosome, and some translocations are linked to certain cancers. An inversion flips a segment within the same chromosome. A duplication repeats a segment. A deletion removes a segment.
Category: Chromosome Errors