Mitosis and Meiosis

[Pages:3]Mitosis and Meiosis

? Mitosis produces two

identical cells ? Stages of mitosis ? Alignment and

separation of chromosomes ? Cytokinesis

? Meiosis produces

genetically variable, haploid, cells ? Sexual life cycle ? Mechanics of meiosis

15 October 2012

Mitosis

[Prometaphase]

Overview of Mitosis

G2 of Interphase

Chromatin (duplicated)

Prophase

Early mitotic spindle

Centromere

Prometaphase

Overview of Mitosis

Metaphase

Metaphase plate

Anaphase

Telophase and Cytokinesis

Cleavage furrow

DNA replication during Interphase

Chromosome, consisting of two sister chromatids

Prophase: Chromosomes begin to condense. Spindle starts to form

Prometaphase Nuclear envelope breaks down. Chromosomes attach to

3

spindle

Spindle

Centrosome at one spindle pole

Metaphase: Chromosomes align in center of cell

Daughter chromosomes

Anaphase: Sister chromatids separate

Telophase: Complete set of chromosomes at each pole

4

Spindle fibers shorten at the kinetochore

Mark

5

Kinetochore

Microtubule

Chromosome movement

Motor protein

Chromosome

Kinetochore Tubulin subunits

6

1

Cytokinesis

Animal cells divide by

constriction

Plant cells build a partition

Cleavage furrow

100 !m

Contractile ring of microfilaments

Vesicles forming

1 !m

cell plate

7

How do the cytoplasmic organelles divide?

? Mitochondria (and chloroplasts) are present in multiple copies, and randomly segregate into the two daughter cells.

? Membrane bound organelles (e.g. ER) fragment along with the nuclear membrane and are reconstructed in the daughter cells

8

The human life cycle

Key

Haploid (n) Diploid (2n)

Gametes are the Haploid gametes (n = 23) Ovum (n) only haploid cells

Meiosis only occurs during gamete formation

MEIOSIS Ovary

Sperm Cell (n)

FERTILIZATION

Testis

Diploid zygote (2n = 46)

Mitosis

Figure 13.5

Multicellular diploid adults (2n = 46)

? Mitosis produces an exact copy of the parent cell.

? Used for growth and asexual reproduction.

? Meiosis produces reduced (haploid) gametes, which are genetically unique.

? Necessary only for sexual reproduction.

Meiosis 1

INTERPHASE

MEIOSIS I: Separates homologous chromosomes

PROPHASE I

METAPHASE I

ANAPHASE I

Sister chromatids

Chiasmata Spindle

Sister chromatids remain attached

Tetrad

Chromosomes duplicate

Figure 13.8

Homologous chromosomes (red and blue) pair and exchange segments; 2n = 6 in this example

Homologous

chromosomes

separate Tertads line up

Pairs of homologous chromosomes split up

Meiosis 2

TELOPHASE I AND CYTOKINESIS

MEIOSIS II: Separates sister chromatids

PROPHASE II

METAPHASE II

ANAPHASE II

TELOPHASE II AND CYTOKINESIS

Cleavage furrow

chromosomes are still double

Figure 13.8

Sister chromatids separate

Haploid daughter cells forming

2

Mitosis vs Meiosis

Not paired

diploid

Homologs pair in meiosis 1

haploid

Sister chromatids separate in meiosis 2

Mitosis vs. Meiosis

? Mitosis

? Conserves the number of chromosome sets

? Daughter cells genetically identical to their parent cell and to each other

? Meiosis

? Reduces the number of chromosome sets from two to one

? Daughter cells genetically distinct from parent cell and from each other

3

 ................
................

In order to avoid copyright disputes, this page is only a partial summary.

Google Online Preview   Download