Chapter 10 Carr
If a diploid cell has 12 chromosome pairs, how many different combinations of chromosomes are possible in gametes after meiosis
212
A gamete from a human male contains
22 autosomes and either an X or a Y chromosome.
A human egg contains
22 autosomes and one X chromosome.
How many chromosomes are in a human gamete
23
In a human cell that is haploid, how many chromosomes are there? How many are autosomes, and how many are sex chromosomes
23 chromosomes: 22 autosomes and 1 sex chromosome
Imagine that a species has eight chromosomes (four homologous pairs). If some event occurred that prevented meiosis from occurring after replication, how many chromosomes would this species have after two generations
32
A cell contains eight chromosomes at the end of prophase I. How many chromosomes will be in each daughter cell at the end of prophase II
4
Which of the following occur during telophase I
Cytokinesis produces two cells that will each
What is one of the cellular differences between human eggs and sperm
Eggs have 200,000 times In a human zygote, where did most of the cytoplasm come from: oocyte
t/f The number of chromosomes present in a human cell at anaphase of mitosis and anaphase of meiosis II is the same
FALSE
What is the result of independent assortment during meiosis
Genetically diverse gametes are produced.
________ is the process in which a single diploid cell divides to produce haploid reproductive cells
Meiosis
From an evolutionary perspective, why is sexual reproduction advantageous over asexual reproduction
Sexual reproduction produces greater genetic diversity than asexual reproduction.
t/f In recombination (crossing over), DNA is exchanged between homologous, non-sister chromatids
TRUE
t/f The X and Y chromosomes are not homologous, but in the meiosis of sperm formation, they pair and separate in anaphase I as though they were homologous
TRUE
How are the products of meiosis and the products of mitosis different
The products of meiosis are gametes.
When a cutting from a plant sprouts roots and yields a new, independent plant, what process has occurred
asexual reproduction
Bacteria (prokaryotes) divide by ________ reproduction, and eukaryotes reproduce by ________ reproduction
asexual; both asexual and sexual
Which of the following processes contributes least to genetic diversity
duplication of DNA
The products of meiosis are
four haploid cells.
A plant branch that regenerates roots and develops into another plant is
genetically identical to the plant from which the branch was taken.
Cells that are ________ possess a single set of chromosomes
haploid
Meiosis II is essentially the same as mitosis except that the outcome produces cells that are
haploid.
In metaphase I ________ are aligned along the metaphase plate, and in metaphase II ________ are aligned along the metaphase plate
homologous chromosomes; pairs of sister chromatids
At what two stages in the human life cycle are diploid cells found
in adult humans and as the zygote
What process produces genetic diversity through random distribution of chromosomes
independent assortment
A difference between spermatogenesis and oogenesis is
meiosis produces four sperm but only one egg.
Random alignment of maternal and paternal homologous chromosomes results in independent assortment
metaphase I
Pairs of sister chromatids line up at the equator, with each one facing opposite poles
metaphase II
Spermatogonia are called stem cells because they develop into two different types of cells. What are they
more spermatogonia and primary spermatocytes
What factors produce genetic diversity in bacteria
mutation and gene transfer
In the process of crossing over
non-sister chromatids of homologous chromosomes exchange genetic material.
In mitosis, cells duplicate their chromosomes once and divide once. In meiosis, cells duplicate their chromosomes ________ and divide ________
once; twice
What is an autosome
one of the non-sex chromosomes
In gamete formation, the starting cells in females are the ________, and the starting cells in males are ________
oogonia; spermatogonia
The primary purpose of meiosis is to ________ the number of chromosomes; meiosis also generates ________ in the resulting cells
reduce or halve; genetic variation
Homologous chromosomes pair up to form a structure called a
tetrad.
What is the flagellum in sperm for
to serve as a structure for the physical propulsion of the sperm
The fertilization of an egg by a sperm produces a cell called a/an
zygote.
If a cell has a haploid number of 5, during mitosis there will be ________ chromosomes at metaphase, ________ chromosomes at anaphase, and ________ chromosomes per daughter cell at telophase
10; 20; 10
A 2n cell from an organism has 40 chromosomes. How many chromosomes would be in a haploid gamete from this organism
20
If a eukaryotic cell has 20 chromosomes and it undergoes meiosis, how many cells will result, and how many chromosomes will they contain
4 cells, each with 10 chromosomes
The haploid number of an organism is 20. A somatic cell from this organism has ________ chromosomes, and its gametes have ________ chromosomes
40; 20
If a 2n cell has three chromosome pairs, how many different combinations of chromosomes are possible in gametes after meiosis
8
Which of the following is true about both sperm and egg production
All resulting gametes are haploid.
Explain why a life cycle that includes meiosis must also include fertilization. What is the advantage of such a life cycle
Because meiosis halves chromosome numbers, there must also be a process (fertilization) that doubles chromosome numbers. Both meiosis and fertilization are sources of variation in populations.
Different species can sometimes interbreed to produce hybrid offspring. For example, the breeding of a horse with a donkey produces a mule. However, these hybrids are usually sterile. A horse will produce gametes with 32 chromosomes, and a donkey will produce gametes with 31 chromosomes, resulting in a mule with 63 chromosomes. Using your understanding of meiosis, propose a reason why mules are sterile
Because the cells have an odd number of chromosomes, one of them will not be able to pair up with a homolog during meiosis. This prevents the proper formation of viable gametes.
T/f At the end of meiosis I, each of the sister chromatids is considered a full-fledged chromosome
FALSE
t/f If an egg is fertilized by a sperm carrying an X chromosome, the resulting child might be either a boy or a girl, depending on the sex chromosome carried by the egg
FALSE
t/f The number of chromosomes present in a cell in metaphase I and metaphase II is the same
FALSE
From the list below, which choice represents a correct difference between sperm production and egg production
Four mature sperm are produced from one cell; one large egg is produced from one cell.
________ have both male and female reproductive parts
Hermaphrodites
Which of the following occurs during anaphase I
Homologous chromosomes are separated.
Imagine you start a population of 1 million bacteria from a single bacterial cell. Now imagine that a population this large is started from a male and female housefly. How would these two populations differ
Individuals of the housefly population would differ genetically from each other much more than would cells of the bacterial population.
What is the result of recombination (crossing over) during meiosis
It creates chromosomes that are a new combination of paternal and maternal material.
In a human female, what happens to the collection of oocytes in the ovaries once puberty begins
One oocyte per month matures and completes meiosis I.
What would the consequence be if spermatogonia were not stem cells
Only a limited quantity of sperm could be produced by males, and then no more could be produced.
Describe the process of meiosis and ova formation in a human female; start with prenatal life, and end with fertilization
Oogonia are produced before birth, up to the seventh month of embryonic life. Some become primary oocytes, begin meiosis, but arrest in meiosis I until puberty. Approximately one oocyte per month matures in the ovary, progressing to meiosis II. Meiosis II is completed after fertilization.
What event occurs in both anaphase of mitosis and anaphase II of meiosis II
Sister chromatids separate.
Describe how sperm and egg cells are different from somatic cells in number of chromosomes (in humans), the cell division processes they undergo and the process that generates them, and the process they undergo to generate a zygote
Sperm and egg cells have 23 chromosomes in humans; somatic cells have 46 chromosomes. Sperm and egg cells are the products of meiosis, but they do not undergo any cell division themselves. Instead, sperm and eggs fuse in fertilization to produce a zygote.
What features of spermatogonia allow males to produce sperm throughout most of their lives? What would happen if the spermatogonia, instead of producing more spermatogonia, divided and produced four gametes
Spermatogonia are diploid stem cells that divide by mitosis to create more diploid spermatogonia. This keeps a reserve of cells that can continue to give rise to more spermatogonia and also to primary spermatocytes to produce sperm. If spermatogonia divided into haploid gametes directly, the reserve of stem cells would be depleted.
t/f In humans, the sperm contributes the chromosome that determines whether the child will be a boy or a girl
TRUE
In meiosis, X and Y chromosomes will pair as homologous chromosomes, but they will recombine only in a few limited regions, at the ends. Explain why recombination is limited in the situation
The X and Y chromosomes contain different genes. In most places, they do not have identical regions to exchange:
Suppose a researcher claims to be able to make a hybrid animal that is a cross between a human and a rhesus monkey. The normal diploid number for humans is 46, and the normal diploid number for rhesus monkeys is 48. Based on normal meiosis, how many chromosomes would the human gamete have, and how many chromosomes would the rhesus monkey have? Given these numbers, how many chromosomes would you expect the hybrid embryo to contain
The human gamete would have 23 chromosomes, and the rhesus monkey gamete would have 24 chromosomes. The hybrid embryo would contain 47 chromosomes.
If crossing over occurs as shown in the figure above, which of the following is true
The result of crossing over is four genetically different chromatids.
If the chromosome number were not halved when gametes are produced, what would be the result of fertilization
The zygote would have double the number of chromosomes as the parents.
Errors in meiosis can be one mechanism of evolution. A change in the number of chromosomes can lead to the production of new species. Some plant species may have originated from errors during cell division, which led to them having more than two sets of chromosomes, a condition called polyploidy. Hypothesize what kind of error during meiosis might occur to cause a normally diploid plant to generate tetraploid offspring, in which the offspring have four sets of chromosomes
There may be a failure of chromosomes to separate during meiosis, producing diploid gametes. If the plant self-fertilizes and a diploid sperm combines with a diploid egg, then a tetraploid zygote would be produced.
What is the fate of sperm that are never released
They are destroyed by the body's immune system.
The cells at the end of meiosis I are not ready to function as gametes. Why not
They are haploid, but the chromosomes are still in duplicated form.
You have homologous pairs of chromosomes in each of your cells. In what way are these pairs of chromosomes identical
They have genes for the same traits.
What is the advantage of ova production resulting in one egg and three polar bodies
This allows the egg to receive most of the cytoplasm.
In birds, the female carries an unmatched pair of chromosomes (denoted WZ), corresponding roughly to the XY chromosomes in mammalian males, and male birds carry a matched set of chromosomes (denoted WW), corresponding to the pair of XX chromosomes in mammalian females. Therefore, in birds the ________ chromosome determines the sex of the offspring, and it is gametes from the ________ parent that determine sex
Z; female
When does an oocyte complete meiosis II
after fertilization
Homologous chromosomes separate
anaphase I
Sister chromatids separate
anaphase II
Once produced, a zygote will divide by ________ to develop into a whole organism
mitosis
In the process of egg production, one cell produced during meiosis will become the egg, and the other three will become
polar bodies.
In humans, which cells undergo meiosis
primary oocytes and spermatocytes
Crossing over occurs during which stage of meiosis
prophase I
Recombination occurs
prophase I
