Lecture 20 by yurtgc548

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									Lecture 20

   Biology 1111
   Chapter 9: Genetics
Today’s Learning Objectives
 Be   able to:
   Perform  blood type Punnett squares
   Explain the polygenic inheritence model

     3 sex-linked diseases
 List
 Explain
   Why   males more likely to be color blind
Dihybrid Cross
 Considers    2 genes
   Each   is independent of the other!
 Gametes   still carry only single copy of
  each gene
 Techniques for Punnett Squares
  basically same
Dihybrid Cross Sample
Question
 On a half sheet
 Show the complete set of Punnett
  squares for this cross:
   Dihybrid cross of homozygous
    Round/Yellow with Green/Wrinkled
   Yellow = Y (capital)

   Round = R (capital)
Correct Answer
Idon’t like book’s
 technique
      Weird square
      Skips F1 square
Two Independent Genes and
Parakeet Color
 In   this case, yellow & blue make green
Two Independent Genes and
Retrievers
 Again,9:3:3:1 ratio
 Be able to do these Punnett Squares
Dihybrid Cross
 Considers    2 genes
   Each   is independent of the other!
 Gametes   still carry only single copy of
  each gene
 Techniques for Punnett Squares
  basically same
Dihybrid Cross Sample
Question
 On a half sheet
 Show the complete set of Punnett
  squares for this cross:
   Dihybrid cross of homozygous
    Round/Yellow with Green/Wrinkled
   Yellow = Y (capital)

   Round = R (capital)
Correct Answer
Two Independent Genes and
Parakeet Color
 In   this case, yellow & blue make green
Two Independent Genes and
Retrievers
 Again,9:3:3:1 ratio
 Be able to do these Punnett Squares
7th   Inning Stretch
Single Gene Human Traits
 Freckles vs. none
 Widow’s peak vs. straight hairline
 Free vs. attached earlobe
One, Two, now Many Genes
 Monohybrid   = one
 Dihybrid = two
 Polygenic = many
   Many human traits are complex
   Controlled by several genes
Polygenic Inheritance
 Example:      skin pigmentation
   Skincolor clearly inherited
   Many, many phenotypes possible
        Not a “light switch”, but a “dimmer”
   Clearly,   single-gene model not sufficient
Polygenic Inheritance (cont’d)
   Book hypothetically uses 3 genes to
    demonstrate
       A = dark, a = light
       B = dark, b = light
       C = dark, c = light
 Overall effect of genes is additive
 Punnett square done same way, but F2
  generation more complex
       8 possible sperms, 8 possible eggs
Note on Skin Pigmentation
 May    be controlled by several genes
   But, tanning (environmental exposure) can
    contribute
   An individual’s ability to cope w/sun genetic

   Therefore, genetics explains only part of
    skin color
 Is   height completely genetic?
To Sum Up
 Polygenic   inheritance
   Might explain traits w/ continuous (dimmer
    switch) states
   Makes genetic research more difficult
Chromosomal Basis of
Inheritance
 1866    Mendel published pea results
   Didn’t   know about DNA, chromosomes
 Early1900’s, biologist begin to see
 parallels in chromosome behavior &
 Mendelian genetics
Sex Chromosomes
X  is large (carries lots of information)
 Y is small (carries little information)
 XX = female
 XY = male
Sex-linked Recessives
 Some  human genetic disorders are
  more common for males
 Why?
Sex-linked Recessives
 Some  human genetic disorders are
  more common for males
 Why?
   Males    have only single copy of X
       If the one X inherited has disorder allele, then
        male is afflicted
   Females     have two X chromosomes
       To have a sex-linked disorder, must inherit 2
        copies of bad allele
Examples of Sex-Linked
Disorders
 Red-green colorblindness
 Hemophilia
 Duchenne muscular dystrophy
Royal Family of Russia

								
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