Chromosomes & Cell Reproduction(Chapters 6 & 7)

I. Cell Division: produces new cells from parent cells & each new cell has a copy of the DNA

A. Why do cells divide?

1. growth and development

2. repair

3. reproduction

B. Types of Cell Division:

1. Binary Fission – occurs in prokaryotes (i.e. bacteria)

a) asexual reproduction: 1 parent cell

splits into 2 identical offspring

b) single, circular DNA

2. Mitosis – occurs in

eukaryotes

a) takes place in

somatic cells

(“body” cells;

not sperm/egg)

b) a copy of DNA (chromosomes) are

passed on to the

newly formed cells

C. DNA and Chromosomes

1. DNA = nucleic acid;

genetic information

(“the code”)

2. gene = segment of

DNA that codes

for a characteristic

3. chromosome = DNA & proteins coiled into a single structure4. chromatids = two exact copies of a chromosome attached at the centromere ;

separate during cell division

D. Each species has a unique # of chromosomes

1. see Table 6-1 page 121

2. Humans – 46 chromosomes

a) 23 homologous chromosome pairs

homologous chromosomes - similar

size, shape, and genes in same

location

one chromosome in each pair is

donated from each parent (23 from

mother & 23 from father)

44 autosomes (22 autosomal pairs)

and 1 pair of sex chromosomes

(XX = female and XY = male)

Sex

chromosomes

Autosomes

b) Somatic cells are diploid (2n) =

have both “sets” in a homologous pair

(humans: 2n = 46 chromosomes)

c) Gamete cells are haploid (n) =

have only 1 set; one of the chromosomes

from each pair (humans: n = 23)

Gametes: sperm (n= 23) & egg (n = 23)

Zygote: egg & sperm join (fertilization) in sexual reproduction

3. Karyotype = photo of chromosomes in a dividing cell

a) can reveal

chromosomal

disorders

b) Types of chromosomal disorders:

1) non-disjunction – too many

chromosomes (fail to separate)

ex: Downs Syndrome = trisomy-21

(extra 21st chromosome)

2) duplication – repeat3) deletion – missing4) inversion – backwards5) translocation – on a different

chromosome

II. The CELL CYCLE

Checkpoints

Cancer• Uncontrolled division of cells

• 2 types of tumors (cell masses)– Benign:

• remains at original site• Can be removed surgically

– Malignant • Cells spread to other locations (metastasis)• Treated with chemotherapy & radiation• New experimental treatments with gold

nanoparticles

III. Mitosis

IV. Meiosis

• A. Forms haploid cells (gametes) for sexual reproduction

• B. Cuts the # chromosomes in half– 1. Haploid (n) = 23 for humans– 2. Sexual reproduction requires fertilization

ovum (egg) & sperm fuse diploid (2n) zygote 23 + 23 = 46

• C. Two nuclear divisions after interphase (G1, S, G2)

• D. Mechanisms of genetic variation

–1. independent assortment – –2. crossing over – –3. random fertilization –

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