chapter 3

Question 1

Mitosis

Answer 1

Divides somatic cells, producing two daughter cells

Question 2

Chromosome

Question 3

Sister Chromatids

Answer 3

The two versions of each chromosome made during the S phase of mitosis

Question 4

Haploid

Answer 4

Single copies of chromosomes (n)

Question 5

Diploid

Answer 5

Two copies of chromosomes (2n)

Question 6

Centromere

Answer 6

Holds the two sister chromatids together

Question 7

Kinetochore

Answer 7

A disc-shaped structure where spindle fibres attach to pull sister chromatids apart

Question 8

Chromosome condensation

Answer 8

Chromosomes condense so that you can see them with the naked eye to prepare to divide

Question 9

Mitotic Cell Cycle

Answer 9

1. G1 phase
2. S phase - DNA synthesis
3. G2 - preparing for M phase
4. Prophase - chromosomes condense and centrosomes move toward opposite poles
5. Prometaphase - nuclear envelope dissolves and centrosomes invade the nucleus
6. metaphase - chromosomes align with sister chromatids facing opposite poles
7. Anaphase - the sister chromatids move to opposite poles (where nondisjunction can happen)
8. Telophase - nuclear membranes reform, chromosomes uncoil, spindlefibres disappear, and cytokinesis

There are checkpoints throughout the cycle

Question 10

Cell cycle checkpoints

Answer 10

Failure leads to apoptosis. At the end of G1, end of S, during G2, and during anaphase

Question 11

Meiosis

Answer 11

The method by which gametes are formed that makes 4 haploid cells out of 1 diploid cell

Question 12

Stages of meiosis

Answer 12

MEIOSIS I
1. Prophase I (crossing over)
2. Metaphase I
3. Anaphase I
4. Telophase I
2 haploid cells

MEIOSIS II
1. Prophase II
2. Metaphase II
3. Anaphase II
4. Telophase II
4 hapoid cells

Question 13

Equational division

Answer 13

Equivalent chromosome number (diploid to diploid or haploid to haploid)

Question 14

Reductional division

Answer 14

Reduction of chromosome number from diploid to haploid in meiosis I

Question 15

What is nondisjunction?

Answer 15

Anomalous chromosome numbers caused by improper segregation during meiosis

Question 16

What are some examples of aneuploidy?

Answer 16

• Down syndrome (trisomy 21) - least severe autosomal trisomy
• Edwards syndrome X (trisomy 18) - severe intellectual disability, decreased muscle tone, low-set ears internal organ defects
• Patae syntrome (trisomy 13) - severe intellectial disability and other problems (90% die 1st year of life)

Question 17

Oogonia

Answer 17

Pecursor cells that get turned into oocytes

Question 18

Primary oocyte

Answer 18

Diploid immature egg cell arrested in prophase I, and remains that way until puberty, when it begins to be stimulated by hormones to complete meiosis I and form a secondary oocyte

Question 19

secondary oocyte

Answer 19

Immature haploid egg cell arrested in metaphase II, and awaits fertilization, after which it will complete meiosis II. If not fertilized, it degenerates

Question 20

Polar body

Answer 20

Two produced from oogenesis. small, nonfunctional cell that has the other set of chromosomes from meiosis and is programmed for apoptosis

Question 21

Mature ovum

Answer 21

FInal haploid product of female gametogenesis that has completed oogenesis

Question 22

Reciprocal cross

Answer 22

two separate crosses for the same trait where the sexes of the parents are reversed, and allows us to examine the effect of sex on phenotypes

Question 23

Characteristics of X-linked recessive conditions

Answer 23

• more males than females will have the recessive phenotype
• generation skipping

Question 24

Characteristics of X-linked dominant disorders

Answer 24

• all carriers of the mutant allele also express the trait
• a father cannot pass the trait to his son

Question 25

Y-linked inheritance

Answer 25

exclusive male-to-male transmission

Question 26

Nondisjunction in meiosis I

Answer 26

the four cells have either two Xs or none

Question 27

Nondisjunction in meiosis II

Answer 27

Two cells with one X each, one cell with two Xs, and one cell with none

Question 28

Dosage compensation in mammals

Answer 28

- In placental mammals, one X is inactivated at random - formation of a barr body inside the cell that has an RNA molecule cover the inactivated chromosome - the long RNA molecule is coded for by the XIST gene - can lead to mosaicism

Question 29

Sex determination

Answer 29

can be environmental or genetic

Question 30

Genetic/chomosomal sex

Answer 30

based on what chromosomes an individual has; multiple types

Question 31

Phenotypic sex

Answer 31

based external appearance; many species have two sexes, some have one, some have more than two

Question 32

Gender identity

Answer 32

based on how someone feels or identifies

Question 33

Sex determination in *Drosophila*

Answer 33

males are the heterogametic (XY) sex. The X/Autosome ratio determines gender - females: X/A of 1 - males: X/A of 0.5 Females have have two X chromosomes and males have one X chromosomes

Question 34

Sex determination in mammals

Answer 34

Determined by the prescence or absence of the Y-linked gene *Sry*

Question 35

ZW sex determination

Answer 35

- female heterogamy (females are hemizygous) - birds, butterflies, moths, some reptiles, fish, and amphibians