Chapter 2: Genes and Medical Genetics

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Chapter 2 Genes and Medical Genetics
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Introduction

• So far, its been all about the cell.
• Last lecture we examined how cells divide. A
  process which facilitates life.
• This time well consider genetic and there impact
  on how we look, and what potential pitfalls may
  occur when cell division and replication dont
  give us what we wanted.

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Introduction

• As always we have several new terms.
• Genotype genes of the individual. Your genetic
  makeup, if you will.
• Phenotype What you look like, or more precisely,
  what physical manifestations are observed.
• Allele Alternate forms of a gene which are
  located in the same position on a pair of
  chromosomes.

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Fig. 02-01

• Three paths
• Two results??
• Not really!
• Again, new terms
• Dominant allele
• (capital letter)
• Recessive Allele
• (lower case letter)

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• As you can see during
• meiotic cell division, alleles
• are isolated within each
• gamete.

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• How do alleles (genes) get mixed up??
• Rem Meiosis? Crossing over??
• Alleles are spread around in an amazing way
  during sexual reproduction.
• As we will see, this leads us to some
  interesting results which dont always seem
  logical.

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• Alleles on autosomes
• Basic Mendelian Genetics
• and the Punnett Square
• If we cross multiply, it
• becomes evident that not
• all genotypes result in the
• same phenotype.
• The example at the left is a
• single-trait cross.
• Notice the expected
• phenotypic ratio (31).
• This will become important
• later.

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• What happens if we
• mix it up a bit??
• Same method, different
• results.
• Now the phenotypic
• ratio is 5050 (Better odds
• than youd get in Vegas!)

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• Okay, Emiril, lets
• Kick it up a notch!!
• Dihybrid crosses
• (and beyond) are
• handled similarly.
• You must be careful
• to transfer all your
• alleles though!!
• Once this is done,
• figuring out what
• you have can be
• challenging.

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Genetic Disorders

• Most of the time, genes are expressed and
  individual live quiet lives.
• Sometimes two alleles get together that
  shouldnt!
• Many are autosomal dominant and expressed with
  alarming frequency.
• In the case of autosomal dominance, even
  heterozygotes express the phentype.

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Genetic Disorders Autosomal Dominant

• Disease Occurence Symptoms
• Neurofibromatosis 1/3500 Dark Spots
• Huntington ?? Neuopathy
• Polycystic Kidney Nephretic cysts/
  hypertension
• renal failure

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Genetic Disorders Autosomal Recessive

• Disease Occurence Symptoms
• Cystic Fibrosis 1/2500 bronchial mucus
• clogged pancreatic ducts
• Phenylketonuria 1/5000 high urinary phenylalanine
  concentration
• Tay-Sachs ?? Blindness, paralysis, death

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• Polygenic Inheritance
• Height, skin color, etc.
• The absolute reason for
• expression of some traits
• such as a persons height
• can be nebulous.
• Many alleles dictate the
• height of an individual, so
• just because your dad
• was 7 doesnt mean you
• will be (though it doesnt
• hurt either).

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Some traits share an additional genetic
component, despite differing environmental
factors
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• Multiple Allelic Traits
• Blood types are coded
• for by three different
• alleles.
• Codominance exists
• because A and B are
• dominant over O.

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• Incomplete dominance
• Paul Mitchell aside,
• hair curls, or lack of
• them are expressed
• as a mixture of straight
• vs. curly locks.
• What can result is a
• continuum of hair curls,
• waves and looks.

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• Incomplete dominance is also observed in
• Sickle-cell Disease. Here homozygotes (HH)
  are normal,
• heterozygotes (Hhs)are carriers, and
  recessives (hshs)
• have the disease. Oddly enough, carriers are
  superior in
• certain environments due to Malaria resistance
  conferred
• by the Sickle-cell trait.

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• Sex-linked traits
• Occur when alleles are
• located on sex chromosomes.
• Sex-linked traits can be harsh.
• Ex. Muscular distrophy
• Hemophilia

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Fig. 02-14
Muscular Distrophy
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Fig. 02-15
Sex-Influence Traits
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Fig. 2D
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Fig. 2C