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 structure 4. 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 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 – repeat 3) deletion – missing 4) inversion – backwards 5) 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 = 46

C.Two nuclear divisions after interphase (G1, S, G2) D.Mechanisms of genetic variation –1.independent assortment – –2.crossing over – –3.random fertilization –