Topic 3.1: Cell Division- Mitosis and Meiosis

Question 1

Describe the cell cycle and explain the maor events that occur during each stage.

Answer 1

G1: The organelles are doubled in the cell, collects the materials to be used for DNA synthesis.

G0: The cells take a break from cell division preparation and resume their normal functions. If DNA is damaged in the cell, they will also enter the G0 phase and apoptosis will occur if the DNA is not reparable.

S: Replication of DNA occurs. One chromatid turns into two (sister chromatids).

G2: The cell synthesizes proteins for cell division.
M: Mitotic stage; the process in which mitosis or cytokinesis occur.

Question 2

Explain why apoptosis is a necessary process.

Answer 2

It removes unwanted tissue and abnormal cells.

Question 3

Define somatic cells

Answer 3

Body cell; excludes cells that undergo meiosis and become sperm or eggs.

Question 4

Define apoptosis

Answer 4

Programmed cell death; involves a cascade of specific cellular events leading to death and destruction of the cell.

Question 5

Define cell cycle.

Answer 5

An ordered sequence of events in eukaryotes that involves cell growth and nuclear division; consists of the stages G1, S, G2, and M.

Question 6

Define interphase

Answer 6

Stages of the cell cycle (G1, S, G2) during which growth and DNA synthesis occur when the nucleus is not actively dividing.

Question 7

Define chromatid

Answer 7

Following replication, a chromosome consists of a pair of sister chromatids, held together at the centromere; each chromatid is comprised of a single DNA helix.

Question 8

Define sister chromatids

Answer 8

One of two genetically identical chromosomal units that are the result of DNA replication and are attached to each other at the centromere.

Question 9

Define Mitosis

Answer 9

The stage of cellular reproduction in which nuclear division occurs; process in which a parent nucleus produces two daughter nuclei, each having the same number and kinds of chromosomes as the parent nucleus.

Question 10

Define cytokinesis

Answer 10

Division of the cytoplasm following mitosis or meiosis.

Question 11

Explain what factors would cause a cell to stop at each of the three cell cycle checkpoints

Answer 11

Cells stop at the G1 checkpoint if conditions are not favorable for cell division and/or there is DNA damage. Cells stop at the G2 checkpoint if the DNA has not finished replicating and/or there is DNA damage. Cells stop at the M checkpoint if the chromosomes are not lined up correctly at the metaphase plate.

Question 12

Summarize the importance of growth factors in regulating the cell cycle.

Answer 12

Growth factors are external signals that promote cell division of target cells.

Question 13

Distinguish between the action of oncogenes and mutated tumor suppressor genes.

Answer 13

Oncogenes encode proteins that continuously promote the cell cycle, leading to unregulated cell division. Tumor suppressor genes function to inhibit the cell cycle. If mutated, the proteins they express would not be active and the cell cycle would continue, possibly leading to cancer.

Question 14

Define growth factors

Answer 14

A hormone or chemical, secreted by one cell, that may stimulate or inhibit growth of another cell or cells.

Question 15

Define proto-oncogenes

Answer 15

Gene that promotes the cell cycle and prevents apoptosis; may become an oncogene through mutation.

Question 16

Define tumor suppressor genes

Answer 16

Gene that codes for a protein that ordinarily suppresses the cell cycle; inactivity due to a mutation can lead to a tumor.

Question 17

Define oncogenes

Answer 17

Cancer-causing gene formed by a mutation in a proto-oncogene; codes for proteins that stimulate the cell cycle and inhibit apoptosis.

Question 18

Distinguish between the number of chromatids each chromosome contains before and after replication

Answer 18

One chromatid before replication; two chromatids after.

Question 19

Summarize the events that are ocurring in each stage of mitosis.

Answer 19

Prophase: The centrosomes move away from eachother toward the opposite side of the nucleus, spindle fibers appear between the separating centrosomes, the nuclear envelope begins to fragment, the nucleolus begins to disappear, the chromatin condenses and chromosomes are visible.

Prometaphase: Kinetochores appear on either side of the centromere and they attach sister chromatids to the kinetochore spindle fibers. The kinetochore fibers attach the sisters to opposite poles of the spindle.

Metaphase: The spindle is fully formed and consists of poles, asters, and fibers. The chromosomes attached to the spindle fibers line up at the metaphase plate.

Anaphase: The sister chromatids separe and become daughter chromosomes and move to opposite poles of the spindle.

Telophase: The spindle disappears and the nuclear envelope reassembles. Each daughter nucleus contains the same number/kinds of chromosomes as the parental cell.

Question 20

Compare and contrast cytokinesis in plant and animal cells.

Answer 20

Both result in two daughter cells with identical genetic material. Animal cells form a cleavage furrow between the daughter nuclei, which is constricted by the action of a band of actin filaments. Plant cells build a new cell wall between the daughter cells by fusing together vesicles produced by the Golgi apparatus.

Question 21

Define chromatin

Answer 21

Network of DNA strands and associated proteins observed within a nucleus of a cell.

Question 22

Define diploid (2n)

Answer 22

Cell condition in which two of each type of chromosome are present

Question 23

Define haploid (n)

Answer 23

Cell condition in which only one of each type of chromosome is present.

Question 24

Define centromere

Answer 24

Constriction where sister chromatids of a chromosome are held together.

Question 25

Define spindle

Answer 25

Collection of microtubules that assist in the orderly distribution of chromosomes during cell division.

Question 26

Define prophase

Answer 26

First phase of mitosis; characterized by the condensation of the chromatin; chromosomes are visible, but scattered in the nucleus.

Question 27

Define prometaphase

Answer 27

Phase of cell division that occurs between prophase and metaphase and is characterized by attachment of the spindle fibers to the kinetochores of each sister chromatid.

Question 28

Define metaphase

Answer 28

Third phase of mitosis; chromosomes are aligned at the metaphase plate.

Question 29

Define anaphase

Answer 29

Fourth phase of mitosis; chromosomes move toward the poles of the spindle.

Question 30

Define telophase

Answer 30

Final phase of mitosis; daughter cells are located at each pole.

Question 31

Define cleavage furrow

Answer 31

Indentation in the plasma membrane of animal cells during cell division; formation marks the start of cytokinesis.

Question 32

Define cell plate

Answer 32

Structure across a dividing plant cell that signals the location of new plasma membranes and cell walls.

Question 33

Outline the major events that occur during meiosis I and II, focusing on the activities of the chromosomes

Answer 33

Meiosis I: Following DNA replication, each chromosome is duplicated. During meiosis I, the homologous chromosomes pair during synapsis and then separate. Meiosis II: During meiosis II, the centromeres divide and the sister chromatids separate, becoming daughter chromosomes that move into the daughter nuclei.

Question 34

Explain why there are two divisions in meiosis and why the DNA is not replicated between meiosis I an meiosis II

Answer 34

In order to divide the DNA content in half; because the DNA was already replicated before meiosis began.

Question 35

Explain how crossing-over and independent assortment introduce genetic variation.

Answer 35

During crossing-over, genetic material is exchanged between nonsister chromatids. This produces a different combination of genes. Independent assortment mixes the whole chromosomes donated by both parents. The end result of both processes is cells that do not have genetic material identical to either parent.

Question 36

Define meiosis

Answer 36

Type of nuclear division that reduces the chromosome number from 2n to n; daughter cells receive the haploid number of chromosomes in varied combinations; also called reduction division.

Question 37

Define homologous chromosomes

Answer 37

Member of a pair of chromosomes that are alike and come together in synapsis during prophase of the first meiotic division; a homologue.

Question 38

Define synapsis

Answer 38

Pairing of homologous chromosomes during meiosis I.

Question 39

Define gamete

Answer 39

Haploid sex cell; e.g., egg or sperm.

Question 40

Define fertilization

Answer 40

Fusion of sperm and egg nuclei, producing a zygote that develops into a new individual.

Question 41

Define crossing-over

Answer 41

Exchange of segments between nonsister chromatids of a bivalent during meiosis.

Question 42

Define independent assortment

Answer 42

Alleles of unlinked genes segregate independently of each other during meiosis so that the gametes can contain all possible combinations of alleles.

Question 43

Define interkinesis

Answer 43

Period of time between meiosis I and meiosis II during which no DNA replication takes place.

Question 44

Describe the differences in the activity of the homologous chromosomes in prophase and metaphase of meiosis I and mitosis.

Answer 44

Meiosis I Prophase I: Pairing of homologous chromosomes Metaphase I: Homologous duplicated chromosomes at metaphase plate Anaphase I: Homologous chromosomes separate Telophase I: Two haploid daughter cells Mitosis Prophase: No pairing chromosomes Metaphase: Duplicated chromosomes at metaphase plate Anaphase: Sister chromatids separate, becoming daughter chromosomes that move to the poles Telophase/ Cytokinesis: Two diploid daughter cells, identical to the parental cell.

Question 45

Compare and contrast the outputs of meiosis and mitosis with regard to the number of cells and the chromosome complement of each cell.

Answer 45

Meiosis II Prophase II: No pairing of chromosomes Metaphase II: Haploid number of duplicated chromosomes at metaphase plate Anaphase II: Sister chromatids separate, becoming daughter chromosomes that move to the poles Telophase II: Fur haploid daughter cells, not identical to parental cell Prophase: No pairing of chromosomes Metaphase: Duplicated chromosomes at metaphase plate Anaphase: Sister chromatids separate, becoming daughter chromosomes that move to the poles. Telophase/Cytokinesis: Tw diploid daughter cells, identical to the parental cell.

Question 46

Summarize the cells in the human body that are haploid and the role these cells play in the life cycle.

Answer 46

Sperm and egg cells are haploid. They function in sexual reproduction..

Question 47

Contrast the number of sperm produced from on primary spermatocyte with the number of eggs produced from on oocyte.

Answer 47

Four sperm; one egg.

Question 48

2. Apoptosis a) decreases the number of cells in the body b) is programmed cell death c) is controlled by enzymes in the cell d) all of the above

Answer 48

d) all of the above

Question 49

At which of the following checkpoints is the DNA checked for damage and, if damage is present, the cell is placed in G0 phase? a) M b)G1 c) G2 d) None of the above

Answer 49

b)G1

Question 50

This checkpoint determines if the DNA has been replicated properly prior to cell division. a) G1 b) S C) G2 d) M

Answer 50

C) G2

Question 51

Which of the following act as the brakes of the cell cycle and prevents cells from dividing too quickly? a) oncogenes b) proto-oncogenes c) cyclins d) tumor suppressor genes

Answer 51

d) tumor suppressor genes

Question 52

Which of the following terms is describes incorrectly? a) prometaphase-the kinetochores become attached to spindle fibers b) anaphase- daughter chromosomes migrate toward spindle poles c) prophase- the chromosomes condense and the nuclear enelope disintegrates d) metaphase- the chromosome are aligned at the metaphase plate e) telophase- a resting phase between cell division cycles

Answer 52

e) telophase- a resting phase between cell division cycles

Question 53

If a parent cell has a diploid of 24 chromosomes before mitosis, how many chromosomes with the daughter cell have? a) 12 b) 24 c) 30 d) 36 e) 64

Answer 53

b) 24

Question 54

Cytokinesis in animal cells involves the formation of a/an a) oncogene b) cell plate c) cleavage furrow d) sister chromatid

Answer 54

c) cleavage furrow

Question 55

If a parent cell has 22 chromosome, the daugter cells following meiosis II will have a) 22 b) 44 c) 11 d) all of the above

Answer 55

c) 11

Question 56

Crossing-over occurs between a) sister chromatids of the same chromosome b) chromatids of nonhomologous chromosomes c) nonsister chromatids of a homologous pair d) non of the above

Answer 56

c) nonsister chromatids of a homologous pair

Question 57

Which of these helps provide genetic diversity? a) independent alignment during metaphase I b) crossing-over during prophase I c) random fusion of sperm and egg nuclei during fertilization d) all of the above

Answer 57

d) all of the above

Question 58

The pairing of homologous chromosomes occurs during which of the following? a) mitosis b) meiosis I c) meiosis II d) all of the above

Answer 58

b) meiosis I

Question 59

Sister chromatids separate during anaphase of which of the following a) mitosis b) meiosis I c) meiosis II d) Both a and c

Answer 59

d) Both a and c

Question 60

Polar bodies are produced during a) DNA replication b) mitosis c) spermatogenesis d) oogenesis e) none of the above

Answer 60

d) oogenesis

Question 61

Following fertilization, the somatic cells of humans divide by a) apoptosis b) meiosis c) mitosis d) DNA replication

Answer 61

d) DNA replication

Question 62

BPA is a chemical compound that has historically been used in the manufacture of plastic products. However, cells often mistake BPA compounds for hormones that accelerate the cell cycle. Because of this, BPA is associated with an increased risk of certain cancers. a) How might BPA interact with the cell cycle of its checkpoints? b) Why do you think very small concentrations of BPA might have a large effect on the cell

Answer 62

a) BPA could increase or decrease the production of cyclins, which would affect cell cycle progress through the checkpoints b) Because BPA acts like a hormone, its effects are amplified within the cell

Question 63

Describe the characteristics of a pedigree for an autosomal dominant and an autosomal recessive trait.

Answer 63

Autosomal dominant: - Affected children will usually have an affected parent - Heterozygotes (Aa) are affected. - Two affected parents can produce an unaffected child - Two unaffected parents will not have affected children - Both males and females are affected with equal frequency Autosomal recessive: - Most affected children have unaffected parents - Heterozygotes (Aa) have an unaffected phenotype - Two affected parents will always have affected children - Closer relatives who reproduce are more likely to have affected children - Both males and females are affected with equal frequency

Question 64

Distinguish between autosomal recessive and autosomal dominant genetic disorders.

Answer 64

Autosomal recessive disorders result from the inheritance of two recessive alleles. The child is affected and is homozygous recessive, but neither parent is because they are heterozygous. In autosomal dominant disorders, both parents are affected but the child can be unaffected.

Question 65

Define pedigree

Answer 65

Chart of genetic relationship of family individuals across generations.

Question 66

Interpret the genotype of the heterozygote if the inheritance pattern for a genetic disorder is shown to be incompletely dominant.

Answer 66

With incomplete dominance, the heterozygote exhibits a phenotype that is intermediate between the homozygous recessive and the homozygous dominant.

Question 67

Determine the genotype of the child, the mother, and the possible genotypes of the father for a child with type O blood who is born to a mother with type A blood.

Answer 67

The mother has to be heterozygous for type A blood, and the second allele for type O blood would have come from the father. He could have been heterozygous for type A, type B, or type O blood.

Question 68

Define incomplete dominance

Answer 68

Inheritance pattern in which an offspring has an intermediate phenotype, as when a red-flowered plant and a white-flowered plant produce pink-flowered offspring.

Question 69

Define codominance

Answer 69

Inheritance pattern in which both alleles of a gene are equally expressed in a heterozygote.

Question 70

Define familial hypercholesterolemia

Answer 70

Genetic disorder that causes an accumulation of cholesterol in the blood due to defects in the LDL receptors on the cell surface.

Question 71

Define multiple alleles

Answer 71

Inheritance pattern in which there are more than two alleles for a particular trait; each individual has only two of all possible alleles.

Question 72

Define polygenic inheritance

Answer 72

Pattern of inheritance in which a trait is controlled by several allelic pairs.

Question 73

Summarize the environmental factors that may influence polygenic traits such as height and skin color

Answer 73

Environmental factors include nutritional status, diet, temperature, and exposure to sunlight.

Question 74

Discuss how studies using identical twins may help determine how much f a phenotype is based on genetics and how much is environmental.

Answer 74

Identical twins have identical genomes and have developed from identical oocytes containing the same cytoplasmic composition. However, the expression of their genes is influenced by environmental inputs. Variation between identical twins is attributed to the inputs from the environment on their development.

Question 75

7. Which of the following does not have an autosomal recessive pattern of inheritance? a) cystic fibrosis b) Huntington disease c) phenylketonuria d) sickle-cell disease e) none of the above

Answer 75

c) phenylketonuria

Question 76

Which of the following does not describe the pedigree analysis of an autosomal dominant disorder? a) heterozygotes are affected b) two affected parents will always have affected children c) affected children usually have an affected parent d) two unaffected parents will not have affected children

Answer 76

b) two affected parents will always have affected children

Question 77

If a child has type O blood and the mother is type A, then which of the following might be the blood type of the child's father? a) A only b) A or O c) B only d) A, B, or O e) O only

Answer 77

a) A only

Question 78

A trait in which the heterozygotes have a phenotype that is intermediate between the dominant and recessive phenotypes is an indication of a) codominace b) pleiotropy c) a sex-linked trait d) incomplete dominance e) none of the above

Answer 78

d) incomplete dominance

Question 79

In the analysis of a genetic disorder, you notice that the phenotypic distribution follows a bell-shaped curve, and that multiple genes are probably involved. This suggests what pattern of inheritance? a) autosomal dominant b) autosomal recessive c) incomplete dominance d) polygenic inheritance e) none of the above

Answer 79

d) polygenic inheritance

Question 80

Which of the following does not have an environmental factor that affects the distribution of the phenotype? a) phenylketonuria b) skin color c) height d) Marfan syndrome

Answer 80

d) Marfan syndrome

Question 81

You are working with the fruit fly Drosophila and want to determine whether a newly found characteristic is dominant or recessive. Design and experiment that will help you determine the dominance of the trait.