Genetics

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Genetics
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Father of Genetics Mendel 1822

• Studied basic principles of inheritance
• No microscopic confirmation till MUCH later

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Used PEAS for study subjects- WHY?

• Grow and reproduce QUICKLY
• Could study one trait at a time
• Flower color
• Seed shape
• Stem length
• Pod shape
• Pod color

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What did he do?

• Began with plants that bred true
• Always produce predictable strains (either Green
  or wrinked seeds EVERYTIME)
• Crossed 2 predictables but different colors
  just to see what happened.

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What did he learn?

• Traits are determined by unit factors (now called
  genes
• Genes passed through gametes
• Since 2 gametes combine offspring are
  determined by a PAIR of genes
• 2 genes that come in different forms called
  alleles (white flowers and red flowers)

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More, what did he learn?

• Off spring that inherit identical alleles from
  each gamete purebred
• Offspring that inherit different alleles are
  hybrid

Aka Pure Bred
Aka Hybrid
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More, what did he learn?

• F1 generation offspring in First Generation

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More, what did he learn?

• Law of Dominance when organism is hybrid for a
  certain trait, but only ONE of 2 alleles is
  expressed, that allele is the DOMINANT allele
  (there are exceptions)

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How symbols work

• RR 2 dominant REDs (flower color)- pure bred
• Rr 1 dominant RED allele, 1 recessive white
  allele-hybrid
• rr 2 recessive alleles- pure bred
• Capital letter for dominant trait, lower case of
  SAME letter for recessive trait

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Genotype? And Phenotype?

• Genotype symbols
• Phenotype trait expression

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Now what Mr.Mendel??

• Were all the rs (recessives) lost in F1 ?
• Mendel crossed 2 hybrids Rr x Rr F2

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What did he learn in the hybrid cross?

• Learned 75 R and 25 r
• Therefore alleles must segregate or separate
  when gametes form. ½ sex cell will receive one
  allele, the other cell will receive the other
  allele.

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Probabilities (mathematics of chance)

• Used to make predictions about traits
• Coin flip 1 coin 50 H, 50 tail
• Both heads 2 coins ½ x ½ ¼
• Punnett square shows probabilities (pg 152)

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Punnett Square in Genetics

• fraction ratio
• 31 Phenotype ratio ?
• 121 Genotype ratio ?

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Now what Mr. Mendel?

• Does the inheritance of one kind of trait
  influence the inheritance of another trait? (Ex.
  Does seed shape effect seed color?)
• Did a dyhybrid cross to answer questions

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Dihybrid

• Does the inheritance of one kind of trait
  influence the inheritance of another trait?

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Law of Independent Assortment

• Inheritance of one allele does NOT affect the
  inheritance of another allele. They are
  independent of each other
• Dihybrid results in 9331 probabilities

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Mendel did NOT discuss Incomplete Dominance

• When BOTH alleles of an allele pair are expressed
  and produce an intermediate trait
• Example Red White Pink (hybrid)

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Chromosomes Theory of Heredity (Sutton Morgan)

• Dont forget allele separation happens during
  meiosis!
• Gene linkage many genes on ONE chromosome
• Obviously genes on the same chromosome can not
  segregate
• Only genes on different chromosomes CAN segregate
  Mendels observations are only true for these

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Chromosomes Theory of Heredity, cont

• Crossing over- increases genetic combination

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Fruit Flies are the peas of today
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Sex Chromosomes

• Female XX
• Male XY
• 50 chance
• Male determine
• Sex type

X X
X
XX
XX
XY
XY
Y
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Sex Linkage

• Does not follow Mendels rules
• Trait linked to sex of organism
• Genes found on the X chromosomes (usually)

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Human Genetics

• Polygenic more than one gene codes for a SINGLE
  trait. Ex skin color may have 6 pairs of genes

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Human Genetics cont

• Pleitrophy a single gene codes for MANY traits
• Example Marfans syndrome 1 gene causes many
  problems
• PKU 1 enzyme missing many problems

Marfans
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Human Genetics cont

• Multiple Alleles
• Blood types pg 166 3 alleles control type (pg
  142)
• What would type O look like?

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Sex linkage in humans

• Most tissues are found on the X chromosome
• Color blindness (red-green)

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Genetics by Pedigree chart

• Hemophelia

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Hemophilia changed history
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Albinism happens several ways