The Basics of Molecular Genetics

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rica_ross
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227274
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The Basics of Molecular Genetics
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2013-07-16 15:07:18
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Biology GRE
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Bioloy GRE
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  1. Mendel
    Developed the basics of genetics
  2. Diploid
    • Organisms have two copies of each chromosome
    • One from mom and one from dad
    • Two alleles for each gene
  3. Alleles
    Different forms of a gene
  4. Genotype
    • Type of genes an organism has
    • Type of alleles
    • EX: GG Gg gg
  5. Phenotype
    Physical features of a gene
  6. Homozygous
    Two copies of the same allele are present
  7. Heterozygous
    One copy of the dominant allele and one copy of the recessive allele
  8. Dominance
    Only one allele that is dominant is needed to produce the dominant phenotype
  9. Law of Segregation
    • Each trait has two alleles so one came from each parent
    • A parent can pass on only one allele to offspring, but not both
  10. Independent Assortment
    • If you are Ww for a certain trait, and Zz for another trait a parent can give a sperm W/w/Z/z
    • Doesn't have to be both dominant or recessive, they are not linked
    • Basically, just because an offspring get a particular allele for one trait doesn't mean it will also receive a particular allele for another trait
  11. Linked Genes
    • Linked genes do not independantly assort
    • the close the linked genes the less likely that the offspring will have a combination of parental phenotypes
    • The offspring are more likely to express parent phenotypes exactly
    • The frequency of mixed phenotypes can be used to map the distance of genes on one chromosome
  12. Pedigrees
    • Square= M
    • Circle=F
    • Shaded figures show a phenotype
    • Those who carry it but do not show it are half shaded
  13. Autosomal and Sex Chromosomes
    • 1-22 Body 23-Sex
    • Sex chromosomes are almost always carried on the X because Y carries limited chromosomes
  14. Autosomal Dominant
    • Male and females equally have chance of trait
    • Does not skip generations
    • Male to male, female to female transmission
    • Trait present if corresponding gene is present (Dominant)
  15. Autosomal Recessive
    • Males and females equally show trait
    • Traits often skip generations
    • Only homozygous individuals have the trait
    • Trait often appears in siblings without appearing in parents
    • If a parent has the trait, the offspring who do not have it are heterozygous carriers of a trait
  16. X-Linked Dominat
    • All daughters of a male who has the trait will also have the trait
    • There is no male to male transmission
    • A female who has the trait may or may not pass the trait on to her son or daughter (will pass on if mother has two affected x's)
  17. K-Linked recessive
    • Trait is far more common in females
    • All daughters of a male who has the trait are heterozygous carriers (assuming their mother did not also pass on the allele)
    • No male to male transmission
    • Mothers of male who have the trait are either homozygous carriers or homozygous and express that trait themselves
  18. Inheritance Keys
    • Males cannot be carriers of X linked traits (Only only x chromosome so they have it or they don't)
    • cannot be a carrier of a dominant trait
    • Dominant alleles are not more popular than recessive
    • Dominant and recessive alleles do not interact
  19. Reccessive alleles
    when transcribed produce defective proteins that cannot perform the given function
  20. Incomplete Dominance
    • Single dominant allele (subject is heteozygous) does not code for enough of a certain protein for the trait
    • Therefore, it does not produce a full phenotype
    • Visualizing resulting phenotype is a blending, however, the alleles do not interact so its really just 50% of the expressing trait
  21. Codominance
    • When two different alleles are present and code for enough proteins so that two different normal proteins are produced (no defective, recessive)
    • The two dominant alleles produce a new phenotype for heterozygous subjects
    • Ex: Blood type
    • Alleles : Ia, Ib, i
    • Iai - Type A
    • Ibi - Type B
    • IaIb - Type AB
    • ii - Type O
  22. Penetrance
    The extend to which a given genes expresses itself in an individual or population
  23. Polygene
    • Ex: Skin color
    • The degree to which a subject expresses the trait depends on the ratio of dominant to recessive alleles one has. 
    • Continuous across a broad spectrum and coded for by multiple genes
  24. Epistasis
    • Occurs when a second gene determines if the first trait is expressed or not
    • Ex: Alleles for trait one B-Blk fur b- Brown
    • Alleles for trait one expression C-Expression c- no expresion
    • BBCc Blk fur shows
    • BBcc - Black but appears colorless
    • bbCc - Brown Fur shows
    • bbcc- Brown but appears colorless
  25. Mitochondrial Inheritance
    • One cellular organelles are derived entirely from the egg/mother (the sperm has no organelles)
    • Therefore, all genes in organelles are from the mother, and diseases based on mitochondrial DNA are passed 100% of the time, and never from the father
  26. Genomic Imprinting
    • Certain alleles seem to be encoded differently depending on which parent alleles they came from
    • Ex: If a recessive gene with disease is passed from mother to offspring is expressed but not if passed from the father.
  27. Triple Repeat Extension
    • Some genes contain end regions with CAG repeats
    • Enzymes for coding can make a mistake and increase the number of repeats
    • These can not show up for generations, because repeats are building up over time, but have not reached the threshold of expression (Genetic anticipation)
    • Ex: Huntingtons
  28. Genetic Anticipation
    Trait builds over generations

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