chromosomes & cell reproduction (chapters 6 & 7)
TRANSCRIPT
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Chromosomes & Cell Reproduction(Chapters 6 & 7)
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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
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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
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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
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C. DNA and Chromosomes
1. DNA = nucleic acid;
genetic information
(“the code”)
2. gene = segment of
DNA that codes
for a characteristic
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3. chromosome = DNA & proteins coiled into a single structure4. chromatids = two exact copies of a chromosome attached at the centromere ;
separate during cell division
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D. Each species has a unique # of chromosomes
1. see Table 6-1 page 121
2. Humans – 46 chromosomes
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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)
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Sex
chromosomes
Autosomes
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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)
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Zygote: egg & sperm join (fertilization) in sexual reproduction
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3. Karyotype = photo of chromosomes in a dividing cell
a) can reveal
chromosomal
disorders
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b) Types of chromosomal disorders:
1) non-disjunction – too many
chromosomes (fail to separate)
ex: Downs Syndrome = trisomy-21
(extra 21st chromosome)
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2) duplication – repeat3) deletion – missing4) inversion – backwards5) translocation – on a different
chromosome
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II. The CELL CYCLE
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Checkpoints
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Cancer• Uncontrolled division of cells
• 2 types of tumors (cell masses)– Benign:
• remains at original site• Can be removed surgically
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– Malignant • Cells spread to other locations (metastasis)• Treated with chemotherapy & radiation• New experimental treatments with gold
nanoparticles
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III. Mitosis
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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
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• 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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