Lesson 9 - Cell Division and Genetics (1-42)

Question 1

Genes

Answer 1

genes code for a specific trait (units of heredity). Segements of DNA

Many genes on one chromosome, a specific locus point on the chromosome

Centresome (middle) and sister chromatids on chromosome

Question 2

Human chromosomes

Answer 2

Somatic cell
46 chromosomes (diploid), two sets of 23, one from each parent

Gametes (sperm and egg cells)
haploids, 1 set of 23 chromosomes, result of meiosis

Question 3

Cell division

Answer 3

Process in which cells reproduce themselves using cell cycle

Some cells divide repeatedly, use stem cells (skin, blood and cheek cells)

Some cells stay alive but don’t divide, active and can repair (muscle and nerve) called cell G0 cells that stay in G1

Other cells divide infrequently (bone)

Question 4

Chromosomes

Answer 4

Replicated in S phase, to prepare for cell division. DNA is replicated and chromosomes condense

Each duplicated chromosome has two sister chromatids (92 total)

Question 5

Cell divison by Mitosis

Answer 5

for eukaryotic cells

Interphase
-chromosomes dulipcate
-cells parts are made
-G1 S and G2 phase

mitosis
- chromatids split
-2 equal cells
-Prophase, Prometaphase, Metaphase, Anaphase, Telophase and Cytokinesis

92 chromatid
46 chromosomes
23 sets

Question 6

Interphase

Answer 6

G1 phase - cell grows, multiple organelles and is active

S phase - cell synthesizes DNA

G2 phase- cell grows, centrioles replicate

Question 7

Prophase

Answer 7

-Chromatin condenses into chromosomes
- Nuclear wall degenerates
-centrosomes starts to move apart (opposite ends)

Question 8

Prometaphase

Answer 8

Intermediate step
- Nuclear envelope disappears
-spindles from chromatids to chromosomes
- Kinetochore proteins appear

Question 9

Metaphase

Answer 9

-centromeres of chromosomes line up at the metaphase plate (midline)
-Mitotic spindles start to form

Question 10

Anaphase “out of here”

Answer 10

-centromeres of chromosomes split
-sister chromatids move toward opposite poles of the cell

Question 11

Kinetochore microtubules

Answer 11

Part of anaphase

Kinetochore microtubules move chromatids toward opposite ends of the cell

Nonkinetechore microtubules
Overlap and push against each other, elongating the cell

Question 12

Telophase

Answer 12

-Mitotic spindle dissolve
-Chromosomes become chromatin
-New nuclear membrane forms
-reverse of prophase

Question 13

Cytokinesis

Answer 13

Splitting of the cell

-divison of cytoplasm
-Occurs with telophase
- Cleavage furrow pinches cell in two (actin-myosin drawstring)

-After cytokinesis, new cells enter interphase

Question 14

The Cell Cycle Control System

Answer 14

Events of the cell cycle are directed by a
control system

-Specific checkpoints to avoid uncesscary division

G1 checkpoint- passed if nutrient sufficient, cell size big enough and DNA undamaged

G2 checkpoint (before mitosis)
- two regulatory proteins involved in cell cycle
-Cyclins and cyclin dependant kinases (cdks)
- Cyclins and cyclin dependant form MPF , a maturing promotor which triggers mitosis

Question 15

External factors

Answer 15

-External cell factors can also trigger cell division
Eg. Growth factor

Density-dependent Inhibition
- Crowded cells stop dividing

Anchorage dependence
- Cells must be attached to substratum to divide

Question 16

Cancer cells

Answer 16

No density-dependent inhibition
-dont care and keep dividing, overrides checkpoint

• form tumours

Question 17

Apoptosis vs Necrosis (cell death)

Answer 17

Apoptosis - “Programmed cell death”
Protective process
* E.g. with cell dysfunction
* May protect us from cancers

Necrosis - Cell death triggered by
inflammation

Question 18

Meiosis

Answer 18

• Sexual reproduction
• Produces a haploid set of chromosomes
  Eg. Eggs and sperm
• Chromosomes replicate once
  2 cell divisions (meiosis I and meiosis II)

Question 19

Meiosis I Meiosis II

Answer 19

Meiosis I- Reduces chromosomes from
diploid to haploid

Meiosis II - Produces four
haploid daughter cells

Question 20

Crossing over important

Answer 20

Exchanging DNA is prophase I

Increases Genetic variability

Produces chromosomes that carry genes from two different parents

Question 21

Interphase and Meiosis I

Answer 21

Interphase - chromosomes dulipcate

Prophase I - 6 total chromosomes, crossing over

Metaphase I - form at midline

Anaphase I - spitting chromosomes to appositive polres

Question 22

Telophase and Cytokinesis I and meiosis II

Answer 22

Telophase I and Cytokinesis I - straight to prophase after split

Prophase II - rid of nuclear membrane

Metaphase II - already haploid, midline

Anaphase II - split to opposite poles

Telophase II and Cytokinesis II - back to chromatid, three unique crossovers

Question 23

Mitosis vs Meiosis

Answer 23

prophase:

while both partake in chromosome replication. Meiosis has the crossing over leading to genetic variability

Metaphase:

In mitosis chromosomes (all 6) are lined up singularly the at metaplate while in meiosis they lined up in parts.

Anaphase and telophase:

In mitosis sister chromatids separate during anaphase to create daughter cells. While in meiosis in anaphase I, homologues separate and sister chromatids remain together creating haploids (telophase I). In Meosis II 4 daughter cells are created and sister chromatids separate in anaphase II.

Question 24

Independent Assortment

Answer 24

Each pair of chromosomes sort its maternal and parental homologues into daughter cells independently of the other pairs

Random assorting

Question 25

Genetic variability

Answer 25

So many combinations, 64 trillion

Independent assortment, random fertilization and crossing over

Question 26

Meiosis malfunction

Answer 26

Abnormal chromosome count
-the failure of homologous pairs to separate during meiosis I
- the failure of sister chromatids to separate during meiosis II

Leads to birth defects

most common is Down syndrome by trisomy 21 (extra copy)