MITOSIS: Brief Review Occurs in somatic cells Somatic cells are the body cells (non-sex cells) ...
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Transcript of MITOSIS: Brief Review Occurs in somatic cells Somatic cells are the body cells (non-sex cells) ...
![Page 1: MITOSIS: Brief Review Occurs in somatic cells Somatic cells are the body cells (non-sex cells) Purposes: replacement of damaged cells, growth of organism.](https://reader030.fdocuments.us/reader030/viewer/2022033106/56649dba5503460f94aaacfa/html5/thumbnails/1.jpg)
MITOSIS: Brief Review Occurs in somatic cells
Somatic cells are the body cells (non-sex cells)
Purposes: replacement of damaged cells, growth of organism
Daughter cells are identical to parent cell
Each division of parent cell produces two daughter cells
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Mitosis: Brief Review In mitosis, chromosome number of
offspring is the same as that of the parent
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Chromosome Number
Somatic cells are DIPLOID Each cell contains 2 copies of each
chromosome (one from each parent) Diploid = 2n
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Human Chromosomes
Each somatic cell contains 46 chromosomes 22 pairs of autosomes
AUTOSOMES = non-sex chromosomes 2 sex chromosomes
pair of X’s (female) An X and a Y (male)
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Reproduction of organisms
Allows for survival of a species Reproduction can be accomplished in
different ways, depending on the organism
Reproduction is regulated by external forces (environmental conditions) and internal forces (hormones) These forces are not mutually exclusive
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Asexual Reproduction
Results in a CLONE A clone is genetically identical to its
parent Advantage: only requires a single
parent Disadvantage: doesn’t allow for
genetic recombination
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Asexual Reproduction
Includes: Binary fission Fragmentation budding
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Budding Hydra
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Sexual Reproduction Allows for gene recombination
Important in survival of species “Survival of the fittest”
There needs to be a mechanism that allows for combination of genes but maintains the normal chromosome number Since 2 parents contribute chromosomes, the
reproductive cells must have half the usual # of chromosomes
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MEIOSIS
The process by which chromosome number is reduced by half.
Results in production of sperm and egg (gametes)
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Chromosome Number
Gametes (egg and sperm) are HAPLOID Each contains just one set of
chromosomes Haploid = n In humans, haploid number is 23
Remember: diploid number is 46
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HUMAN CHROMOSOMES
46 CHROMOSOMES IN SOMATIC CELLS: 22 homologous pairs plus 2 sex chromosomes
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Karyotype Arrangement of homologous pairs of
chromosomes Used in genetic counseling or to diagnose a
baby’s condition.
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HOMOLOGOUS CHROMOSOMES
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Homologous chromosomes
Are called HOMOLOGUES One is from male parent; one is from
female parent
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MEIOSIS
“reduction division” gametes have half the diploid number of chromosomes
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Fertilization
The combination of gametes (egg and sperm
Results in a ZYGOTE Restores the diploid number
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MEIOSIS
CONSISTS OF 2 SUCCESSIVE DIVISIONS: MEIOSIS I, MEIOSIS II
ALLOWS FOR EXCHANGE OF GENETIC MATERIAL
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Meiosis
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Meiosis
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Synapsis of Prophase I
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CHROMOSOMES
Once DNA has replicated, the chromosomes are composed of 2 sister chromatids, joined by a centromere
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TETRAD
A replicated pair of homologous chromosomes
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Crossing Over
Genetic information is exchanged between homologous chromo- somes. Chiasma (plural = chiasmata) is site of crossing over
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Crossing Over
Can you identify the chiasmata?
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Meiosis: Summary
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Meiosis: A summary
2 nuclear divisions resulting in 4 haploid cells
Random mixture of paternal and maternal genes This occurs by crossing over of
homologues Occurs in Prophase I
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Meiosis