Lesson 1

Cell cycle

Chromosomes

Mitosis phases

Organism Diploid chromosome # (2n) in body cells

Haploid chromosome # (n) in gametes

Human *(memorize) 46 23Goat 60 30Guinea pig 64 32Bat 44 22Squirrel 40 20Alligator 32 16Chicken 78 39King crab 208 104Fruit fly 8 4Pea 14 7Apple 34 17Potato 48 24Soybean 40 20Lettuce 18 9Rice 24 12Leopard Frog 26 13

Lesson 2

Meiosis phases

Metaphase I

Prophase I

Anaphase I

Telophase I

Prophase II

Telophase II

Anaphase II

Metaphase II

Cells can divide in two different ways…

MITOSIS MEIOSIS

11

Organism Diploid chromosome # (2n) in body cells

Haploid chromosome # (n) in gametes

Human *(memorize) 46 23Goat 60 30Guinea pig 64 32Bat 44 22Squirrel 40 20Alligator 32 16Chicken 78 39King crab 208 104Fruit fly 8 4Pea 14 7Apple 34 17Potato 48 24Soybean 40 20Lettuce 18 9Rice 24 12Leopard Frog 26 13

12

Meiosis I

Metaphase I Anaphase I

13

Meiosis II

Metaphase II

Anaphase II

14

Mitosis MeiosisIn what types of cells does

it occur?

What type of reproduction is

this process involved in?

How many divisions

occur?

Number of daughter cells

produced?

Chromosome number of

daughter cells produced?

Genetic comparison with

the original cell?

Does crossing over occur?

Comparison Chart

15Table 3.1

Comparison of Mitosis and Meiosis

16

Meiosis• Cell division that produces gametes with half

the number of chromosomes

• Occurs in special cells called germline cells

found in the gonads

• Maintains the chromosome number of a

species over generations via fertilization

• Ensures genetic variability via the processes

of independent assortment and crossing

over of chromosomes

17

Meiosis consists of two divisions

- Meiosis I = The reduction division

- Reduces the number of chromosomes

from 46 to 23

- Meiosis II = The equational division

- Produces four cells from the two

produced in Meiosis I

Note: Each division has the 4 phases (PMAT)

Prophase, Metaphase, Anaphase, Telophase

18

Meiosis

Figure

3.3

19

Figure

3.4

Meiosis I

20Figure

2.3

Prophase I

• Homologs pair-up

and undergo

crossing over

• Chromosomes

condense

• Spindle forms

• Nuclear

envelope/membrane

breaks down

21Figure

2.3

Crossing-over

Figure

3.5

• Paired chromosomes

(homologs) exchange

genetic information

resulting in genetic

variation in each

gamete produced

• Occurs during

synapsis in Prophase I

22Figure

2.3

Metaphase I

• Homologous pairs

align along the cell’s

equator

• Random alignment

pattern determines the

independent

assortment of

chromosomes in the

gametes

23Figure

2.3

Independent Assortment

Figure

3.6

24Figure

2.3

Anaphase I

• Homologs separate

and move to opposite

poles of the cell

• Sister chromatids

remain attached at

their centromeres

25Figure

2.3

Telophase I

• Nuclear envelope

reforms

• Spindle disappears

• Cytokinesis divides

the rest of the cell

into two

26Figure

2.3

Interkinesis

• A short interphase between the two

meiotic divisions

• Chromosomes unfold into very thin

threads

• Proteins are manufactured

• However, DNA is NOT replicated a

second time

27

Meiosis II (same as Mitosis)

Figure

3.4

28Figure

2.3

Prophase II Metaphase II

• Chromosomes

align along the

equator

• Chromosomes

condense and

become

visible again

• Spindles form

• Nuclear

envelope

degenerates

29Figure

2.3

Anaphase

II• Centromeres

divide

• Sister

chromatids

separate to

opposite cell

poles

Telophase

II• Nuclear

envelope

reforms

• Chromosom

es uncoil

• Spindle

disappears

30Figure

2.3

Results of Meiosis

• Four haploid cells

containing a single copy

of the genome (23

chromosomes each)

• Each cell is unique –

carries a different

assortment of genes and

chromosomes

Lesson 3

Gametogenesis

- spermatogenesis

- oogenesis

32Figure

2.3

Gametogenesis• The process in which cells undergo meiosis

to form gametes

33Figure 3.7Figure

3.7

Spermatogenesis

34Figure

2.3

Spermatogenesis• Occurs in the seminiferous tubules of the testes,

beginning at puberty continuing throughout the

man’s life

• A diploid spermatogonium divides by mitosis to

produce a stem cell and another cell that specializes

into a primary spermatocyte

• In meiosis I, the primary spermatocyte produces two

haploid secondary spermatocytes

• In meiosis II, each secondary spermatocyte

produces two haploid spermatids

• Spermatids then mature into tad-pole shaped

spermatozoa (4 sperm cells in total)

35Figure 3.7

Spermatogenesis

Figure

3.8

36

37

Sperm

Structure

Figure

3.9

• Acrosome contains

digestive enzymes

to help penetrate

egg

• Mitochondria

provide energy

• Tail provides

motility

38Figure 3.7

Oogenesis

Figure

3.11

39Figure

2.3

Oogenesis• Unlike spermatogenesis, oogenesis is a

discontinuous process

• Meiosis begins during fetal development of

female

• Oocytes pause development at prophase I

until puberty

• After puberty, meiosis I continues in one or

several oocytes each month but halts again

at metaphase II

• Meiosis is only completed if the ovum is

fertilized

40Figure

2.3

OogenesisA diploid oogonium divides by mitosis to

produce a stem cell and another cell that

specializes into a primary oocyte

In meiosis I, the primary oocyte divides

unequally forming a small polar body

and a large secondary oocyteIn meiosis II, the

secondary oocyte

divides to form

another polar body

and a mature haploid

ovum

41Figure 3.7Figure

3.12

Oogenesis