Unit 4 - Cell Cycle and Communication

Question 1

List 3 differences between asexual reproduction and sexual reproduction

Answer 1

Sexual reproduction begins from two parents while asexual reproduction begins from a single individual.

In sexual reproduction, both parents contribute genes to the offspring in the form of the fusion of gametes during fertilization. Asexual reproduction does not have a fusion of gametes since the single parent passes copies of all its genes to the offspring

Sexual reproduction results in more genetic variation in the offspring, as their genomes are different from each other and the parents. Asexual reproduction results in genetically identical offspring because they arise from mitosis and have the exact copies of the parent’s genes. Asexual offspring are called clones.

Question 2

What are gametes? (definition, function, chrromosomes)

Answer 2

Reproductive cells that transmit genes from one generation to the next; haploid (n = 23 chromosomes)

Contain 22 autosomes and one sex chromosome (X in females, X or Y in males)

EX: sperm and ova (eggs)

Question 3

What is a locus?

Answer 3

The location of a gene on a chromosome

Question 4

What is a somatic cell?

Answer 4

All cells in the body that are not gametes; diploid (2n = 46 chromosomes)

Contain 46 autosomes

Question 5

What is a karyotype? What are the similarities in homologous chromosomes?

Answer 5

Picture of an organism’s complete set of chromosomes, arranged in pairs of homologous chromosomes or homologs.

One homologous chromosome was inherited from your mother and one from your father. Both chromosomes in a pair carry genes at the same loci that control the same inherited characteristics (EX: eye color) but may have different alleles (EX: blue eyes vs brown eyes). Both are similar in length + centromere position and have the same staining pattern

Question 6

Sex chromosomes (X and Y)

Answer 6

Human females have a homologous pair of chromosomes, XX, but human males have one X chromosome and one Y chromosome (XY).

Question 7

Autosome

Answer 7

Nonsex chromosomes (all other 22 pairs)

Question 8

How do meiosis and fertilization contribute to the life cycles of sexually reproducing organisms?

Answer 8

Meiosis halves the number of chromosome sets from two (2n) to one (n), and then fertilization combines two gametes to double it from one (n) to two (2n), thus restoring the diploid number to form a zygote, or a fertilized egg, that eventually grows into an organism with diploid somatic cells. Fertilization and meiosis alternate in the life cycles of sexually reproducing organisms.

Question 9

List 4 differences between meiosis and mitosis

Answer 9

Mitosis occurs in somatic (body) cells while meiosis occurs in gametes (sex cells)

Mitosis produces 2 diploid daughter cells (46 chromosomes) that are genetically identical to the parent and to each other. Meiosis produces 4 haploid daughter cells (23 chromosomes, one from each homologous pair) that genetically vary from one another and the parent

The # of divisions in mitosis is 1 while the # of divisions in meiosis is 2. However, they both experience DNA replication only once

The purpose of mitotic division is to grow and repair identical cells and also for asexual reproduction while the purpose of meiosis is to create unique gametes for fertilization

Question 10

What do 2n and n each represent?

Answer 10

Diploid number (2n) = # of chromosomes

Haploid number (n) = # of homologous pairs

Question 11

List 3 unique events that occur during meiosis I but do not occur in mitosis.

Answer 11

1. Synapsis and crossing over between homologous chromosomes, which creates genetically varied daughter cells [prophase I]
2. Alignment of homologous pairs (tetrads) at the metaphase plate. In mitosis, individual chromosomes line up, but in meiosis I, pairs of homologous chromosomes line up. This results in independent assortment (two ways in which the maternal pair and the paternal pair can line up), which increases genetic variation [metaphase I]
3. Separation of homologous chromosomes. In mitosis, the sister chromatids separate while in meiosis I the pairs separate so that the sister chromatids remain attached [anaphase I]

Question 12

List 3 ways in which meiosis creates genetic variation.

Answer 12

1. Independent Assortment of Chromosomes

Random orientation of homologous pairs occurs at the metaphase plate in metaphase I. There is a 50% chance that a given daughter cell gets the maternal chromosome pair and a 50% chance it gets the paternal chromosome pair. Each pair is positioned independently of the other pair which means they are sorted independently.

2. Crossing Over

During prophase I, genetic material is exchanged between homologous chromosomes (nonsister chromatids) which produces recombinant chromosomes that carry genes from both parents. All the chromatids that make up the tetrad are different due to crossing over. On top of that, at metaphase II, chromosomes can be oriented in two different ways because their sister chromatids are no longer identical. This creates even more genetic possibilities in the daughter cells

3. Random Fertilization

Due to the previous two mechanisms, each gamete is already unique. There are even more possible combinations from the fusion of a male gamete (a sperm cell) with a female gamete (an egg) to produce a diploid zygote

Question 13

Formula for # of possibilities of daughter cells?

Answer 13

2^n with n being the haploid number

Question 14

How does negative feedback help maintain homeostasis?

Answer 14

In a negative feedback loop, feedback serves to reduce an excessive response and keep a variable within the normal range. Examples of processes controlled by negative feedback include body temperature regulation (sweating when you’re hot to lower your body temp) and control of blood glucose.

Question 15

How does positive feedback affect homeostasis?

Answer 15

In a positive feedback loop, feedback serves to intensify a response until an endpoint is reached. Examples of processes controlled by positive feedback in the human body include blood clotting and childbirth

Question 16

Centromere

Answer 16

The region where two sister chromatids are most closely attached to each other

Question 17

What are the 3 stages of interphase?

Answer 17

1. G1 phase - cell grows by producing proteins + cytoplasmic organelles such as mitochondria
2. S phase - replication of DNA and centromeres
3. G2 phase - more growth, preparation for mitosis

Question 18

Definition of mitosis

Answer 18

Division of one nucleus into two genetically identical nuclei

Question 19

Centrosome

Answer 19

Where the assembly of microtubules for the mitotic spindle begins in animals

Question 20

Name the stages of mitosis in order

Answer 20

Prophase
Prometaphase
Metaphase
Anaphase
Telophase

Question 21

Prophase

Answer 21

chromatin fibers condense into discrete chromosomes viewable under a light microscope

mitotic spindle begins to form (centrosomes, microtubules, asters)

centrosomes move away from each other toward the poles of the cell, propelled by lengthening microtubules between them

Question 22

Prometaphase

Answer 22

nuclear envelope fragments

kinetochore microtubules (which are attached to the centromere of each chromosome on each side) jerk them back and forth

non-kinetochore microtubules interact with those from the opposite pole of the spindle, elongating/shortening the cell

Question 23

Metaphase

Answer 23

centrosomes are at opposite poles of the cell

chromosomes line up at the metaphase plate

Question 24

Anaphase

Answer 24

cohesin proteins holding the sister chromatids together at the centromere are cleaved –> two sister chromatids separate –> each becomes its own chromosome

the daughter chromosomes begin moving toward opposite ends of the cell as their kinetochore microtubules shorten

non-kinetochore microtubules lengthen, elongating the cell

Question 25

Telophase

Answer 25

two daughter nuclei form in the cell

two nuclear envelopes arise from the fragments of the parent cell

chromosomes become less condensed and loosen up into chromatin fiber

the mitotic spindle is disbanded

Question 26

Nondisjunction

Answer 26

Occurs when the members of a pair of homologous chromosomes don’t separate properly during meiosis I or sister chromatids don’t separate properly during meiosis II/mitosis. One daughter cell gets two and one gets none

Spindle fibers don’t attach

Question 27

Definition of cytokinesis

Answer 27

Division of the cytoplasm into two identical daughter cells

Question 28

Cytokinesis in animal cells

Answer 28

1. Formation of a cleavage furrow - a shallow groove in the cell surface in the middle
2. A contractile ring of actin microfilaments with the protein myosin pinches the cell in two like a drawstring - process is called cleavage
3. Two separate daughter cells arise

Question 29

Cytokinesis in plant cells

Answer 29

1. Vesicles from the Golgi Apparatus carry materials to form a cell plate between daughter cells
2. After it finishes growing, it fuses with the plasma membrane
3. Two separate daughter cells arise

Question 30

Binary fission

Answer 30

Division of prokaryotes (bacteria) and the asexual reproduction of unicellular eukaryotes

1. The single circular chromosome replicates and the cell elongates
2. Once the cell has reached twice its size, the plasma membrane pinches inward and divides the cell into two separate daughter cells

Question 31

Which phase do nerve cells and muscle cells spend the most time in?

Answer 31

G0 phase where they do not undergo mitosis/cell division

Question 32

Growth factor

Answer 32

A protein released by certain cells that stimulates other target cells to divide

Question 33

Why can only diploid cells undergo meiosis?

Answer 33

Only diploid cells can undergo mitosis because haploid cells have a single set of chromosomes (n = 23) that can’t be further reduced

Question 34

Prophase I

Answer 34

Centrosome movement, spindle formation, chromosome condensation, and nuclear envelope breakdown occur just like in prophase of mitosis

Each chromosome pairs with its homolog, aligned gene by gene, and crossing over occurs

Question 35

Chiasmata

Answer 35

These are X shaped regions each homologous pair has where crossovers have occurred (where the different colors meet)

Hold homologous chromosomes together until anaphase I

Question 36

Metaphase I

Answer 36

Pairs of homologous chromosomes line up at the metaphase plate, with one facing each pole

Question 37

Anaphase I

Answer 37

Kinetochore microtubules pull the homologous chromosomes apart while the sister chromatids remain attached together at the centromere (essentially separate the maternal chromosome and the paternal chromosome)

homologous chromosomes move toward opposite poles

Question 38

Telophase I and Cytokinesis

Answer 38

Each half of the cell has a haploid set of chromosomes (n) with chromatids that contain regions of non-sister chromatid DNA

Cytokinesis forms 2 haploid daughter cells

No chromosome duplication occurs between meiosis I and meiosis II

Question 39

Metaphase II

Answer 39

Homologous chromosomes line up at the metaphase plate just like in mitosis

because of crossing over, the two sister chromatids of each chromosome are not genetically identical, which creates genetic variation in offspring

Question 40

Anaphase II

Answer 40

Cohesin proteins holding the sister chromatids together at the centromere are cleaved –> two sister chromatids separate –> each becomes its own chromosome

the daughter chromosomes begin moving toward opposite ends of the cell as their kinetochore microtubules shorten

non-kinetochore microtubules lengthen, elongating the cell

Question 41

Telophase II and Cytokinesis

Answer 41

Two nuclei form, chromosomes decondense, cytoplasm divides

4 haploid daughter cells are produced from 1 parent cells; they are all genetically distinct from each other and from the parent

Question 42

How does synapsis/crossing over occur?

Answer 42

Synapsis is the joining of homologous chromosomes along their length. This newly formed structure is called a tetrad and it aligns the chromosomes gene by gene

In crossing over, the DNA from one homolog (or parent) is cut and exchanged with an exact corresponding portion of DNA from the other homolog (or parent). The points of attachment where crossovers occurred are crisscrossed regions called chiasmata, which hold the homologs together until anaphase I

Question 43

G1 checkpoint

Answer 43

Go ahead checkpoint

If a cell gets a signal to divide (signaling molecules called growth factors), then it will bypass the check point and divide

If not, the cell will enter a nondividing state (G0 phase)

Question 44

G2 checkpoint

Answer 44

This will determine if the cell has enough size and organelles, that the DNA has been replicated (completely & correctly). The cell is now ready to divide

Question 45

M checkpoint

Answer 45

Occurs near the end of metaphase stage of mitosis

Determines that all the spindle microtubules are attached to the sister chromatids to prime for their separation

Question 46

Describe the process in eukaryotes that ensures that the number of chromosomes will not double from
parent to offspring when gametes fuse during fertilization.

Answer 46

Homologous pairs of chromosomes separate in meiosis I which results in haploid (n) gametes, each receiving only one member of each chromosome pair.