Cell Reproduction n Mitosis – asexual reproduction –1 cell produces 2 identical cells n Meiosis...

Cell Reproduction

Mitosis – asexual reproduction– 1 cell produces 2 identical cells

Meiosis – sexual reproduction– 1 parent cell produces 4 cells with ½ the

number of chromosomes as the parent

Why Cells Divide

Growth

Repair

Reproduction

When Cells Divide

Surface Area/Volume Ratio determines the maximum size of any cell.

Cells can’t get bigger, so they divide.

Terminology

Parent cells for new daughter cells

Chromosomes contain DNA & genes

Homologous Chromosomes (a pair)

Phases of Mitosis

Interphase

Chromosomes are uncoiled DNA replicates Centrioles replicate

INTERPHASE

DIVISION

Prophase

Chromosomes coil - appear double stranded

Nucleolus & nuclear membrane disappear

Centromere and chromatids are visible Centrioles form aster rays & spindle

fibers as they move to the poles

Metaphase

Double stranded chromosomes individually line up on the equator

Centromeres attach to a spindle fiber CENTROMERE

CHROMATIDCENTRIOLE

Anaphase

Chromosomes split & separate and are pulled to opposite poles of the cell by the spindle fibers

Telophase

Cytoplasm divides (cytokinesis) New nuclear membranes form

Cell Division and Reproduction

Sexual Reproduction– 2 parents needed.– Offspring are similar to, but not

identical to the parents.– Genetic variations contribute to

evolution of species.

Chromosome Number

Each species has a specific chromosome number.

Homologous chromosomes - 2 of a same pair. Have the same number and types of genes. One from egg, other from sperm.

Gametes - reproductive cells. Have half the chromosome number. They have only one chromosome of each pair.

Chromosome Number

Haploid - half chromosome number Sex cells (n)

Diploid - pairs of chromosomes Body cells (2n)

Meiosis - reduction division reduces chromosome number to haploid.

Phases of Meiosis

One DNA replication followed

by two cell divisions.

Interphase I

DNA replicated

Centrioles replicated

Prophase I

Chromosomes coil Centrioles move to poles Spindle fibers and asters form Nuclear membrane disappears Homologous chromosomes

synapse & crossing over occurs

Metaphase I

Homologous chromosomes line up at the equator in pairs

Crossing over occurs between homologs

Anaphase I

Homologous chromosomes separate and move to poles

Telophase I

Cytokinesis occurs forming 2 haploid cells

Cells contain double stranded chromosomes at this point

Interphase II

No DNA replication

Chromosomes uncoil

Centrioles replicate

Rest same as Mitosis

Prophase II - Chromosomes coil.

Metaphase II - Line up on equator.

Anaphase II - Split at centromere and move to opposite poles.

Telophase II - Cytokinesis results in 4 haploid cells.

Spermatogenesis

Sperm cell formation 4 equal sized gametes form

46D46

23D

23D

23

23

23

23

Oogenesis

Egg cell formation 1 large egg + 3 polar bodies (die)

46 46D

23D

23D

23

23

23

23

Mitosis vs. Meiosis

23

46

46

23D 23D

23 23 23 23

Meiosis

Mitosis

Diploid Cells

FertilizationHaploid

Cells

Gametes

Zygote

Genetic Variations

Sexual reproduction (fertilization)

Meiosis - independent assortment

Meiosis - crossing over

Random Mutations