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2n = 46, how many tetrads are in this cell
23: a tetrad is a PAIR of chromosomes, and there are 2 sets of each for a total of 46 chromosomes
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after 1st round of mitosis and into meiosis at metaphase II, how many chromatids are present from a starting of 2n = 10
5 chromatids are now present due to the separating of homologous chromosomes during meiosis I
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Cell division purpose
- 1. development from a fertilized cell
- 2. growth
- 3. repair
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Prior to cell division
- DNA needs to be replicated
- Organelles have to be replicated
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centromere
center of chromosome
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sister chromatids
duplicate top or bottom bunny ear looking pairs of genes
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cell cycle control proteins
- 1. cyclins (mostly in M phase)
- 2. cyclin dependent kinases (CDKs)
- can combine to MPF allowing to pass into mitosis
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Cell control for mitosis in yeast
- Paul nurse discovered CDC 2, controls G2 --> M phase
- humans is CDK
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external signals & checkpoints for mitosis
growth factors: proteins stimulate division
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Internal signals for growth
- 1. density dependent inhibition (if dense, will stop growth)
- 2. anchorage dependency (need something as a base)
- TUMORS do not follow either of these
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Pangenesis
particles in the blood determine your place (royal blood)
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Leeuwenhoek idea
believed Sperm contained an actual little baby
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Blending Theory
Recognized there was a MIX of 2 parents…like PAINT
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Lamarck
Theory of inheritance of acquired characteristics (ie: giraffe necks)
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Mendel
- studied peas (self fertilizing & pure breeding)
- cross polinated different plants and looked at traits
- particulate inheritance: particles are passed down from generations
- saw the following:
- NO blending of char.
- males & females contribute equally
- Aquired traits NOT inherited (anti Lamarck)
- each parent contributes
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Incomplete Dominance
- 3:1 -> 1:2:1
- ie red, pink, white (pheno reflects geno ratio)
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Codominance
- heterozygotes show pheno of BOTH homozygotes
- ie blood groups AB (except O, which is complete dominance, A or B overpower O, but A does not overpower B)
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Lethal Allele
- 3:1 -> 2:1
- ie: spina bifida in humans, the dominant allele is deadly (ie: AA = dead)
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Pleiotropic
mutations w/multiple effects
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Semilethal
- Only SOME individuals of a certain genotype die
- ie: drosophilia which lacks ADH, only die IF encounter alcohol in its lifetime
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Epistasis
- Allele of one gene eliminates the ability to recognize a phenotype from another gene
- ie either a recessive (aa) does not allow any phenotype to form, doesn't matter what B is for example. Could also be dominant (A_) does not allow phenotype to form, regardless of any other genes.
- Recessive Epistasis = 9:3:3:1 -> 9:3:4
- Dominant Epistasis = 9:3:3:1 -> 12:3:1
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Complementary Genes
- 9:3:3:1 -> 9:7
- REFER to handout
- mutations in different genes give the same phenotype
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Duplicate Genes
- 9:3:3:1 -> 15:1
- 2 genes can provide normal fxn, BUT only if BOTH are recessive can a change occur
- ie chlorophyll can't be made if aabb (so white), otherwise if A_ or B_ will be green
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Penetrance
% of individuals that show the PHENOTYPE associated w/the genotype
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Expressivity
- Degree that a GENOTYPE is exhibited in the phenotype
- ie mutant which turns things red, the % red = penetrance, but if some are MORE red vs others, this is expressivity
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Linkage
different genes on same chrom do NOT show independent assortment
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