Mendelian Genetics

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Mendelian Genetics

• How Genes Work

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Who Are You?

• Phenotype
• How you look PHysical appearance

• Genotype
• Your genetic makeup GENEs

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Father of Genetics

• Modern genetics began with Gregor Mendels
  quantitative experiments with pea plants

Stamen
Carpel
Figure 9.2A, B
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• Mendel crossed pea plants that differed in
  certain characteristics and traced the traits
  from generation to generation

White
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Removed stamensfrom purple flower
Stamens
Carpel
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Transferred pollen from stamens of white flower
to carpel of purple flower
PARENTS(P)
Purple
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Pollinated carpel matured into pod

• This illustration shows his technique for
  cross-fertilization

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Planted seeds from pod
OFF-SPRING(F1)
Figure 9.2C
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Genetics Basics

• Chromosomes occur in pairs, one from MOM, one
  from DAD (homologues)
• Genes are carried on chromosomes
• Genes code for a trait or characteristic (I.e.
  hair color)
• Alternate forms of that trait are called ALLELES
  (ie. Blond, brown, redhead, etc)

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Alleles

• Alleles can be dominant or recessive
• Heterozygous vs. homozygous
• Only way to see a recessive trait?

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Mendel s basic laws

• Law of Segregation
• Law of Independent Assortment

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• The chromosomal basis of Mendels principles

Figure 9.17
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Walter Suttons Theory of Chromosomal
Inheritance(Mendels proof)

• Gametes contribute to heredity via nuclear
  material (chromosomes)
• Homologues segregate during meiosis
• Homologues separate independently of other
  homologous pairs

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Probability

• Mathmatical model of how often specific events
  will happen
• of occurances/ of attempts

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Punnett Square

• Visual representation or model of
• what alleles can be present in gametes
• how those alleles can recombine in offspring
• Used to determine the probability of offsprings
  genetic makeup

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Monohybrid Cross

• One gene
• 2 alleles considered (one from mom, one from dad

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Dihybrid Cross

• 2 genes
• 4 alleles considered

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How can we determine Homo- vs. heterozygous
individuals?

• Test Cross
• Must use homo recessive to conduct cross in order
  to see the questionable allele

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What Mendel Didnt See

• Multiple alleles
• Codominance
• Epistasis
• Polygenic traits or Continuous Variation
• Pleiotropy
• Incomplete Dominance or blended inheritance
• Environmental Effects
• Sex linked and sex influenced traits

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CoDominance

• Both alleles expressed at the same time both
  dominant

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• Incomplete dominance neither allele is fully
  dominant (blended inheritance)

Figure 9.12Ax
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Epistasis

• Sequential action of genes
• Product of one gene influences another (one gene
  gives permission for another allele to work
• Gene action acts as a biochemical pathway
  feedback inhibition
• Ex Indian corn coloration

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Pleiotropy

• Where one allele may have multiple effects on
  phenotype

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• Normal and sickle red blood cells

Figure 9.14x1
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Individual homozygousfor sickle-cell allele
Sickle-cell (abnormal) hemoglobin
Abnormal hemoglobin crystallizes,causing red
blood cells to become sickle-shaped
Sickle cells
Clumping of cells and clogging of small blood
vessels
Breakdown of red blood cells
Accumulation ofsickled cells in spleen
Heart failure
Pain and fever
Spleen damage
Physical weakness
Brain damage
Damage to other organs
Anemia
Impaired mental function
Pneumonia and other infections
Kidney failure
Rheumatism
Paralysis
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Continuous Variationor Polygenic Traits

• Multiple genes acting to influence a
  characteristic
• Produces gradual changes, not distinct borders
• Ie. Height, weight, nose length, skin pigment

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P GENERATION
aabbcc(very light)
AABBCC(very dark)
F1 GENERATION
AaBbCc
AaBbCc
Sperm
Fraction of population
Skin pigmentation
F2 GENERATION
Figure 9.16
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Environmental Influence

• Example color change of fur in arctic animals

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Same eyes, different lighting
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Multiple Alleles

• More than one allele per gene

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• 3 alleles (ABO)
• 4 phenotypes (A, B, AB, O)
• Uses concept of glycoproteins (sugar name tags or
  antigens) to mark cells
• Non-recognition of the correct name tag for
  blood type can cause agglutination

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Landsteiner Blood Groups

• Type A galactosamine AA (homo) or AO (hetero)
• Type B galactose BB or BO
• Type AB galactosamine galactose (codominant)
• Type O no sugar marker - OO

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Blood Donor Facts

• Universal Donor

• Universal Recipient

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Rh factor

• Rh factor can be or
• is like a seen name tag or antigen
• - is invisible
• Rh- moms that have Rh babies are subject to
  spontaneous abortions
• Erythroblastosis fetalis
• Controlled with an injectionof RhoGam to hide
  babies cells

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Sex Linked

• Sex on the X
• Specific trait/disorder is found on sex
  chromosome, usually the X
• Usually recessive traits
• Seen more often in males than females
• Ex color blindness, hemophilia

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Barr Body inactivation

• In females, both X chromosomes are not
  metabolically active
• Random inactivation of one X chromosome may
  influence traits expressed