Lecture 8a

Question 1

When does mitosis and meiosis happen for plants and animals?

Answer 1

Mitosis happens:
After fertilization
During growth & development
To replace dead or damaged cells: stem cells divide (stem cells in animals found throughout the body; plants have stem cells in limited areas)

Meiosis happens
only in gonads in animals &
in specialized structures in plants

Question 2

Cell division & chromosome number

Answer 2

Mitosis: chromosome number of daughter cells same as parent cell
Meiosis: chromosome number of daughter cells ½ the number same as parent cell

Question 3

2 categories of chromosomes: autosomes & sex chromosomes

Answer 3

In humans: autosomes: # 1 to 22 (chromosomes are numbered based on size, shape, genes present)
Sex chromosomes: 23rd chromosome: X or Y

Question 4

Karyotype

Answer 4

Karyotype: profile of a person’s chromosomes

Question 5

How many sets of chromosomes do gametes and body cells have?

Answer 5

Gametes have 1 set (1n) of chromosomes; body cells have 2 sets (2n) - diploid cells
Gametes
23 chromosomes (1n)
22 autosomes +
1 sex chromosome

Fertilized egg & Body cells
46 chromosomes (2n):
44 autosomes +
2 sex chromosomes

Question 6

What is a set of chromosomes?

Answer 6

Chromosomes come in matched sets known as homologous pairs.

The 46 chromosomes of a human cell are organized into 23 pairs, and the two members of each pair are said to be homologues of one another (with the slight exception of the X and Y chromosomes, see below).

Question 7

Alleles:

Answer 7

alternate versions of genes on homologous chromosomes

2 alleles:
1 says curly hair: GGGCATGCCAATT
1 says straight hair: ATGCATGCCAATT

Question 8

Homologous pair of chromosomes:

Answer 8

each with genes for the same characters. One inherited from mom, one inherited from dad.

Question 9

Gene:

Answer 9

: A segment of DNA at a specific locus on a specific chromosome. It contains the info for making an RNA: if mRNA, then it codes for a particular protein (ex D codes for lactase)

Question 10

A pair of alleles.

Answer 10

Alleles: alternate versions of the same gene pair. The alleles can code for the same version of the trait (both code for a long nose) or different versions (one codes for a long nose, the other for a short one)

Question 11

Sex chromosomes: 2 copies for each allele?…it depends

Answer 11

Females have 2 copies of all 800 genes on the X-chromosome.
775 in the X-specific region + 25 in the homologous region

Males have 2 copies of the 25 genes in the homologous region of the y-chromosome.
1 copy of the 775 genes in the X-specific region
1 copy of 55 genes in the
y-specific (differential) region
slide 17

Question 12

Fertilized egg & all somatic cells have …. set(s) of chromosomes

Answer 12

Fertilized egg & all somatic cells have 2 sets of chromosomes

23 chromosomes in egg (1-22 + X) +
23 chromosomes in sperm (1-22 + X or Y)

After fertilization you (zygote) have 46 chromosomes:
44 autosomes + 2 sex chromosomes

Question 13

What do stem cells do?

Answer 13

Stem cells in the gonads:
1. Stem cells that maintain the stem cell population go through the cell cycle that includes mitosis. 1 cell → 2 → 4 → …

2. In response to hormones, some of the stem cells go through the cycle that includes meiosis. These germ cells will become gametes: they are haploid cells that have left the cell cycle.

Stem cells in the rest of the body
1. Stem cells that maintain the stem cell population: go through the cell cycle that includes mitosis. 1 cell → 2 → 4 → …

2. Stem cells that receive a chemical signal that causes them to become a differentiated cell leave the cell cycle. → bone cells, neurons,…

Question 14

Cell cycle or not

Answer 14

Cells in cell cycle: stem cells
Interphase: G1,S,G2
Cell division (mitosis)
Cytokinesis
Back to interphase
If it remains a stem cell (no differentiation occurs), then it may go through mitosis & cytokinesis again

When cells become differentiated they leave the cell cycle
Cells are in Go
Performing their job (ex making hormones)
Make new organelles as needed

Question 15

For stem cells throughout the body & in the gonads: Cell cycle

Answer 15

interphase, mitosis, & cytokinesis

Question 16

Production of gametes cell cycle

Answer 16

Cell Cycle: interphase, meiosis, & cytokinesis (only in the gonads)

Question 17

Interphase

Answer 17

Interphase is exactly the same, whether cell will go through mitosis or meiosis

The cell is preparing for cell division
3 PARTS:
G1 (Gap 1): Most organelles are replicated.

S phase: copy all the chromosomes. Synthesize (make) DNA & the associated proteins

G2 (Gap 2): centrioles (needed in cell division) duplicated + make other proteins that will be needed

Question 18

Go

Answer 18

When a cell differentiates (ex becomes a muscle cell), it stops dividing, so it leaves the cell cycle.
It’s said to be in Go

Question 19

Interphase: S phase

Answer 19

S= synthesis phase

Chromosomes duplicated: each now consists of 2 identical sister chromatids
Chromosomes duplicated (aka replicated): each chromosome now consists of 2 identical sister chromatids, connected at their centromeres.

Connected at their centromeres

Question 20

Chromatid vs chromosome

Answer 20

1 replicated chromosome made up of 2 sister chromatids
Each chromatid made up of 1 double-stranded DNA molecule and its associated proteins

When 2 sister chromatids separate, each chromatid now called a chromosome: have now 2 unreplicated chromosomes.

Question 21

How are the sister chromatids held together?

Answer 21

Cohesion (a complex of many proteins)

Centromere:
Highly condensed region of DNA

At anaphase, an enzyme cleaves off much of the cohesion complex, allowing the sister chromatids to be separated