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Fundamentals of Genetics

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7 characteristics each with 2 contrasting traits. Ex: plant height ... Ex: RR= red, RR'= roan (red & white), R'R'= white. Problem: Heterozygote x Heterozygote ... – PowerPoint PPT presentation

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Title: Fundamentals of Genetics


1
Fundamentals of Genetics
  • Genetics Heredity
  • Chapter 9

2
Fundamentals of Genetics
9-1 Mendels Legacy
9-2 Genetic Crosses
3
Gregor Mendel Pea Plants
  • 7 characteristics each with 2 contrasting traits
  • Ex plant height (tall or short)
  • Self-pollination v. Cross-pollination
  • Experiments
  • Parental (P1) generation cross contrasting
    traits
  • 1st Filial (F1) generation self-pollinate
  • 2nd filial generation (F2)
  • Results
  • F1 generation all 1 trait (ex tall)
  • F2 generation 31 ratio (tall short)

4
Mendels Conclusions
  • Law of Dominance
  • Dominant allele v. Recessive allele
  • Alleles alternative forms of 1 gene (height-
    tall)
  • Capital letter dominant (ex tall T)
  • Lowercase letter recessive (ex small t)
  • Law of segregation
  • Pair of alleles separate during formation of
    gametes
  • Law of independent assortment
  • Alleles on separate chromosomes or far apart on
    same chromosome separate independently of each
    other (ex tall/ short separate from green/
    yellow)

5
Genetic Terminology
  • Genotype Gene make-up
  • Alleles inherited
  • Ex Height TT, Tt, tt
  • Phenotype Physical appearance
  • Ex Height
  • TTtall
  • Tttall (tall dominant)
  • tt small
  • HomozygousPurebred
  • Alleles in pair alike
  • Hom. Dominant
  • Ex Height
  • Genotype TT
  • Phenotype Tall
  • Hom. Recessive
  • Ex Height
  • Genotype tt
  • Phenotype small
  • HeterozygousHybrid
  • Alleles in pair different
  • Ex Height
  • Genotype Tt
  • PhenotypeTall

6
Probability
  • Likelihood specific event occurs
  • Expressed as decimal, fraction, percentage
  • Eqn times event expected to happen
  • opportunities for event to happen
  • Example
  • Mendels F2 generation
  • Dominant yellow seed color occurred 6,022 times
  • Recessive green seed color occurred 2,001 times
  • Probability of yellow 6,022/ 8,023 0.75100
    75
  • Probability of green 2,001/ 8,023 0.25 100
    25
  • Many trials more likely to get predicted results

7
Predicting Monohybrid Crosses Height
  • Monohybrid cross cross of one trait
  • Punnett Square diagram to predict offspring
  • Homozygous Dominant x Hom. Recessive
  • Step 1 determine parents
  • Height? TT x tt
  • Step 2 Put parents on punnett square
  • Step 3 Predict
  • Step4 Genotypic Phenotypic ratios
  • Genotypic- 0 TT4 Tt 0 tt
  • Phenotypic- 4 Tall 0 Short

8
Monohybrid Cross Height
  • Homozygous Dominant x Heterozygous
  • Step 1 ID parents
  • Step 2 add parents to Punnett
  • Step 3 Predict
  • Step 4 Genotypic Phenotypic ratios
  • Genotypic ratio
  • Phenotypic ratio
  • Homozygous recessive x Heterozygous
  • Genotypic ratio
  • Phenotypic ratio

9
Monohybrid Cross
  • Heterozygous x Heterozygous
  • Ratios
  • Testcross
  • Determine unknown genotype of phenotypic dominant
    trait
  • Unknown Dominant x recessive
  • OR
  • Ratios Ratios

10
Complete Incomplete Dominance
  • Complete Dominance
  • One allele completely dominant
  • Heterozygote dominant phenotype
  • Incomplete Dominance (4 oclock flower)
  • 2 or more alleles influence phenotype
  • Heterozygote intermediate phenotype
  • Ex RR red, Rr pink, rr white
  • Problem Heterozygote x Heterozygote
  • Ratios

11
Codominance
  • Codominance (horse)
  • Both alleles expressed
  • Heterozygote mixed phenotype
  • Ex RR red, RR roan (red white), RR white
  • Problem Heterozygote x Heterozygote
  • Ratios

12
Dihybrid Crosses
  • Cross 2 pairs of contrasting traits
  • Ex seed texture seed color
  • Hom. Round Yellow x Hom. Wrinkled Green
  • Step 1 determine parents
  • RRYY x rryy
  • Step 2 determine possible gametes ( indep
    assort)
  • RRYY? RY, RY, RY, RY
  • rryy? ry, ry, ry, ry
  • Step 3 Set-up Punnett Square
  • Step 4 Predict
  • Step 5 Phenotypic ratios

13
Dihybrid Cross Punnett Square
Phenotypic Ratios Round Yellow 16 Round Green
0 Wrinkled Yellow0 Wrinkled Green0 Ratio
16000
14
Dihybrid Cross
  • Heterozygous x Heterozygous
  • Step 1 ID parents
  • Step 2 Determine possible gametes
  • Step 3 Put gametes in Punnett Square
  • Step 4 Predict
  • Step 5 Phenotypic Ratio

15
Dihybrid Cross
Phenotypic Ratio Round Yellow Round
Green Wrinkled Yellow Wrinkled Green Ratio
Heterozygous x Heterozygous
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