GENETICS IN A NUTSHELL

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GENETICS IN A NUTSHELL

• BY LINDA HEIDENRICH
• BIOLOGY

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THE BASICS

• Dominant represented by a large letter trait
  that is expressed
• Recessive represented by a small letter trait
  that is masked unless in the homozygous form
• Genotype genes in an organism
• Phenotype outer appearance from the genes

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MORE BASICS

• AAhomozygous dominant
• Aaheterozygous
• aahomozygous recessive
• AA or Aadominant trait
• aarecessive trait

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Autosomal Trait

• An autosome is a gene found in the body cells,
  i.e. not found on sex chromosomes.
• Genetics follow basic heredity rules regarding
  dominance and recessiveness.
• EXAMPLE Mendels peas
• Combine TT (homozygous tall) and Tt (heterozygous
  tall)What do you get?

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Welcome the Punnett Square

• A Punnett Square explains the possible outcomes
  for a mating.

T T
T TT TT
t Tt Tt
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So

• A cross between a homozygous tall and a
  heterozygous tall would yield
• 50 probability of getting homozygous tall plants
  as offspring
• 50 probability of getting heterozygous tall
  plants as offspring
• HOW do you get a short plant?
• Think, Pair, Share

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Well

• Either cross tt x tt or Tt and tt
• Try the Punnett Square for each

T t
t
t
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Sex-Linked

• Trait on a gene found on X or Y chromosome
• Usually are recessive disorders-apparent only in
  the homozygous recessive form
• Common example red-green colorblindness in boys
  or hemophilia

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Sex-Linked Trait Notation

• Notation
• Male with trait XhY
• Male without trait XHY
• Female with trait XhXh
• Female without trait XHXH
• Carrier female XHXh
• TRY ONE Cross a hemophiliac male and a carrier
  female.

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Incomplete Dominance

• Autosomal traits BUT the heterozygous phenotype
  is a combination of the two homozygous phenotypes
• Example Color in snapdragons
• RRred
• Rrpink
• rrwhite
• TRY ONE Cross a pink snapdragon with a red
  flower.

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Co-dominance

• Autosomal traits BUT the heterozygous is BOTH
  homozygous traits. NO RECESSIVE
• Example Horse Coloring
• RRRed
• RRRed/White (Roan)
• RRWhite
• TRY ONE Cross a two roan horses.

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Blood Types

• Combination of Co-dominance and dominant and
  recessive patterns
• AB blood IA IB
• A blood IA IA or IA i
• B blood IB IB or IB i
• O blood ii
• TRY ONE Cross a heterozygous A blood female with
  a homozygous B blood male.