Human Genetics

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Human Genetics Genetic Studies
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Quick Review

• 46 chromosomes
• 22 pairs of autosomes
• 1 pair of sex chromosomes
• XX ? XY ?
• 30,000 genes
• 3,100,000,000 bases

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Genetic Studies

• Not all traits follow Mendels Law of Dominance
• Variations
• Sex determination
• Sex linked
• Polygenic Traits
• Incomplete Dominance (blending)
• Codominance (two phenotypes)
• Multiple Alleles
• RH factor in the blood

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Sex Determination

• Early 1900s Morgan discovered that animal
  gender is determined by the X and Y chrom.
• Females XX
• Males XY

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Boy or Girl?

• Y chromosome produces a protein that shuts off
  the X chromosome
• Leads to male development
• Females only need one X, so extra X is shut off
  at random in each cell
• Turned off X called a Barr body
• Leads to calico cats

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Sex Chromosomes ?

• Turner Syndrome XO
• Sterile, underdeveloped female
• Klinefelters Syndrome XXY, XXXY
• Sterile, long arms and legs, shy
• Triple X XXX
• Fertile, taller than average

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Sex Linked

• Traits whose genes are found on the X Chromosome
• Genotypes
• XX normal female
• XX1 normal female carrier
• X1X1 - abnormal female
• XY normal male
• X1Y abnormal male
• Example
• Red green colorblindness
• Hemophillia

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Sex-linked Cross

• What are the odds of a son being colorblind if
  his moms dad was colorblind, but his mom and dad
  were normal?
• XBXb x XBY

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Sex linked Practice

• Janes father was a hemophiliac and her mother
  was normal / non carrier. What are the odds that
  their son will be affected?

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Polygenic Traits

• Many traits are controlled by more than one gene
• Traits show wide variation
• Ex Skin color, height, eye color, and fur
  color, IQ, bell pepper color

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Incomplete Dominance / Codominance

• Neither allele is dominant
• Heterozygous phenotype is a blend of both
  homozygous phenotypes
• Ex wavy hair, snapdragon flowers, blood types

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Incomplete Dominance
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Multiple Alleles

• Traits whose genes have more than 2 alleles
• Each individual only gets two, but there are more
  than two in the population
• Ex Rabbit fur color and blood types

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Multiple Alleles

• Human Blood Types A, AB, B, O
• IAIA, IAIO Type A
• IBIB, IBIO Type B
• IAIB Type AB
• IOIO Type O

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Blood Types

• Multiple alleles IA, IB, i

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Multiple Alleles
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Whos the Baby Daddy?

• Bob has homozygous A blood. He marries Jane who
  has AB blood. What are the possible blood types
  of the offspring?
• Betty has Type O blood. She has a child that has
  type A blood. Can he be the father?

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Blood Type Problems

• Two couples had babies in the same hospital at
  the same time and the babies got mixed up.
  Doctors determine whose baby is whose using blood
  type analysis. The Johnson couple has blood
  types of B and AB the Smith couple has blood
  types of B and A. Baby 1 has a blood type of A
  and Baby 2 has a blood type of O. Which baby
  belongs to which couple?

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Pedigrees

• Diagram used to show how traits are inherited in
  a family
• Like a genetic family tree

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Extra Chromosomes?

• Nondisjuction in gametes during metaphase I,
  sometimes the homologous chromosomes dont
  separate
• Usually lethal, except in chr. 21 and sex chr.
  (13 18 rarely trisomy)
• Extra 21 Trisomy 21 or Down Syndrome

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Cystic Fibrosis

• Most common in Northern Europeans and their
  descendants
• 1/2500 births
• Recessive disorder
• Lungs clog with mucus, digestive problems

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Sickle Cell Anemia

• Most common in Africans and their descendants
• Protects against malaria
• Malaria protist cant infect sickle cells
• Better to be heterozygous, than to not carry the
  sickle cell allele in areas with malaria

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Other Genetic Disorders

• Tay sachs defective form of an enzyme. Causes a
  build up of fatty tissue in the nervous system
• Phenylketonuria (PKU) lacks an enzyme needed to
  metabolize a specific amino acid. Babies have
  brain damage and black urine

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Detecting Disorders

• Genetic Screening Karyotype
• Finding Deformities
• Ultrasound
• Fetoscopy uses a camera to take pictures
• Ways to get cell samples
• Amniocentesis
• Chorion villi sampling
• DNA fingerprinting