Homework: 11-4 worksheets

Daughter cells are clones of each other And of the original parent

Interphase

Somatic cells:

Mitosis

Germ cells: Meiosis

Daughter cells are unique to each other And have half the DNA of the original parent

In humans, one set of chromosomes consists of 23 chromosomes. The haploid number (n) equals 23.

Photograph of chromosomes grouped in order of pairs

Interphase

Just like before Mitosis, Interphase includesGrowth, Protein Synthesis and DNA Replication.

M e i o s i s I

Interphase

M e i o s i s I I

M e i o s i s I

Prophase I

Telophase I

Anaphase I

Metaphase I

Prophase II

Telophase II

Anaphase II

Metaphase II

M e i o s i s I I

Meiosis Overview:Start: Diploid germ cell with homologous chromosomes (2n=46)

Replicate DNA: still diploid, now 2 identical copies of DNA

Meiosis I: homologous chromosomes separate, now haploid (n=23), sister chromatids attached

Meiosis II: haploid (n=23), sister chromatids separate

2nd Meiotic division

(haploid)

1st Meiotic division (haploid)

After DNA Replication

(diploid)

(diploid male germ cell)

Finished Sperm

cells (haploid)

2nd Meiotic Division (haploid)

After DNA Replication

(diploid)

(diploid female germ

cell)1st Meiotic Division (haploid)

first polar body

(haploid)

three polar bodies

(haploid)

Independent assortment › Each gamete you produce contains one of

roughly 8 million possible combinations of chromosomes inherited from your mother and father.

Random fertilization› The random fusion of a single sperm with a

single ovum during fertilization will produce a zygote with any of about 64 trillion (8 million × 8 million) combinations of chromosomes!

Factor these in with Crossing Over

1 2 3

Independent assortment: Chromosomes line up during metaphase I independently of each other.

…the resulting gametes have a different assortment of chromosomes

Two types of gametes

Mitosis MeiosisWhat is produced? More Cells New Organism

Cell Similarity Identical Cells Similar Cells

Cell Type Somatic ‘body’ Cells

Gametes- sex cells

Egg, Sperm

# of Divisions 1 Division 2 Divisions

Diploid/Haploid Cells

2 Diploid Cells 4 Haploid Cells

Chromosome # 46 chromosomes/cell

23 Chromosomes/cell

N ? 2N- 2 copies N- 1 copy

In Mitosis Cell division makes

two clones of the parent cell

For growth, healing and asexual reproduction

Maintains the same number of chromosomes

In Meiosis Cell division makes

four unique daughter cells

With half of the DNA of the parent cell

To make sperm cells and egg cells (gametes)

Reduces the number of chromosomes by half

Spindles do not attach properly during metaphase, and chromosomes or chromatids do not separate.

Results in too many or not enough chromosomes in gametes

Klinefelter’s Syndrome: XXY

Turner’s Syndrome: X

Down’s Syndrome: Trisomy 21

Deletion When part of the chromosome breaks off

Duplication When part of the chromosome repeats itself

Inversion When two parts of a chromosome flip

Translocation when one part of a chromosome breaks off, then reattaches in the wrong place

Cri du Chat Syndrome: Deletion from Chromosome 5

Emanuel Syndrome: Translocation of 11 and 22

Chromosome 15q Duplication Syndrome: Diagnosed with Autism

Meiosis occurs to form gametes for sexual reproduction

It involves forming 4 haploid daughter cells

Because of Crossing over, Independent Assortment and Random Fertilization, it increases genetic variability

Nondisjunction can result in the incorrect number of chromosomes.

Somatic cells Gametes Haploid (n) Diploid (2n) Homologous chromosomes Tetrad Crossing over