Biology 1111

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Lecture 19

• Biology 1111
• Chapter 9 Mendelian Genetics

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Todays Learning Objectives

• From Chapter 9
• Be able to
• Perform basic Punnett Square
• Define discuss
• Pedigrees
• Cystic fibrosis
• Carriers
• Huntingtons, Alzheimers
• Amniocentesis, CVS, Ultrasound

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Overview of Generations
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Generations in Parakeets
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Sample Problem

• Q Show the complete set of Punnett Squares for
  this cross in pea plants
• White flowers X Homozygous Purple Flowers
• Be sure to label P1, F1, F2 generations
• P Purple, p white

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Back to Fundamentals

• There is a strategy for this kind of problem
• Step 1 Consider the genes
• Step 2 Show the cross
• Step 3 Label your gametes (eggs sperms)
• Step 4 Set up your Punnett Square

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Step 1 Consider the Genes

• We know that weve got purple and white flowers
• The symbols are
• Purple P
• Purple is capital P, because its dominant
• White p
• White is lower case p, because its recessive

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Step 1 (Contd)

• Why is dominant/recessive important?
• PP purple flower (easy, homozygous)
• pp white flower (easy, homozygous)
• Pp purple flower (hmmheterozygous)
• NOT light purple, because P is dominant

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Step 1 (Contd)

• So far
• One gene, for flower color
• Two alleles, P and p
• Is everyone with me so far?

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Step 1 (Cond)

• Q Show the complete set of Punnett Squares for
  this cross in pea plants
• White flowers X Homozygous Purple Flowers
• We must have pp X PP. Why?
• Homozygous both alleles same (PP)
• Heterozygous alleles are different (would be Pp)

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Step 2 Show the Cross

• White flowers X Homozygous Purple Flowers
• pp X PP

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Step 3 Gametes

• White can produce either p or p
• Purple can produce either P or P

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Step 4 Set up Punnett Squares

• Usually
• Male gametes across top
• Female gametes down left side

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7th Inning Stretch
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Homologous Chromosomes

• Alleles are located on same location
• We have 2 of each allele, therefore 2 of each
  chromosome

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Pedigrees

• The family tree of genetics
• Squares males
• Circles females
• Open symbol unafflicted
• Closed symbol afflicted

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Carriers

• Heterozygous for recessive disorder
• Has just one bad allele
• Asymptomatic (single allele has no effect)

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Cystic Fibrosis

• Most common U.S. lethal genetic disorder
• Recessive
• 1 in 25 Caucasians carries it
• A carrier if single allele
• Afflicted if two copies of allele
• Overly thick mucous

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Other Concerns w/ Recessives

• Chances of 2 carriers mating is usually low
• UNLESS the mates are also relatives

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Dominant Disorders

• Single or both alleles will give disorder
• Some are lethalhow can these exist?

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Dominant Disorders

• Single or both alleles will give disorder
• Some are lethalhow can these exist?
• Disorders occur late in life (after reproduction)
• Huntingtons disease
• Some Alzheimers

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Early Detection

• Amniocentesis
• CVS
• Ultrasound

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Amniocentesis

• Fluid around fetus chemically analyzed
• Small sample of cells from fluid incubated in lab
  (for a few weeks), then analyzed

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Chorionic Villus Sampling (CVS)

• Bigger sample of fetal cells from placenta
• Advantages
• No cell incubation necessaryfaster
• Can detect abnormalities earlier in pregancy
• Disadvantages
• Some risks to fetus and mother

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Ultrasound

• Sonar picture in the womb
• So far, very safe
• Easy, non-invasive
• Readily available

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What to do with Information

• These methods can detect various abnormalities
• If tests positive, then parents can prepare or
  make other choices

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Ethical Question

• Insurance companies dont cover pre-existing
  conditions
• Should it be legal for insurance companies to
  require early detection?
• Should it be legal for insurance companies to
  exclude these children from coverage?

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Incomplete Dominance

• Hybrids are intermediate in phenotype
• Hybrid snapdragons have pink flowers (red white
  parents)
• Sickle cell anemia in humans
• 1 copy of allele no anemia, but malaria
  resistant
• 2 copies of allele sickle cell anemia

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3 Alleles ABO Bloodtypes

• Blood cells can have substance A, substance B,
  both, or none
• IA allele for substance A (dominant)
• IB allele for substance B (dominant)
• i allele for no substance (recessive)

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Question

• Little Bobbys blood type is A
• His mom has type O
• What are two possible genotypes for his father?
• Hint
• Punnett Squares
• We get half our alleles from one parent