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Fundamentals of Genetics
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I. Introduction to Genetics
1. Gregor Mendel - “Father of Genetics” Austrian monk, teacher, scientist, gardener Formulated basic laws of heredity in the early 1860s
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2. Worked with garden peas because:
Easy to grow and had a short generation time Could be self-pollinated 3. Chose varieties that were true-breeding No genetic variation for a trait 4. Studied 7 simple traits
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5. Mendel cross-pollinated plants
P = parental generation F1 = first-generation (sons/daughters) F2 =second-generation
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6. Principle of Dominance and Recessiveness
F1 plants resembled only one of the parents F1 hybrids contained two different factors (alleles) for each trait one dominant; (masks recessive); one recessive; (seems to disappear)
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Which are you?
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7. Principle of Segregation
Organism contains two factors for each trait. Alleles separate from one another during formation of gametes. Each gamete contains one allele for each trait.
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8. Principle of Independent Assortment
Each trait is independent of another Genes of one pair of traits assort independently All combinations of genes occur in gametes
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II. Chromosomes, Genes, & Genetic Crosses
Homologous Chromosomes contain genes (locations on DNA for traits) for the same traits Traits are controlled by alleles (alternative forms of a gene). 3. Genotype refers to the alleles an individual receives at fertilization 4. Phenotype refers to the physical appearance of the individual.
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5. Homozygous dominant genotypes =
two dominant alleles for a trait. (BB) 6. Homozygous recessive genotypes = possess two recessive alleles for a trait (bb) 7. Heterozygous genotypes = one of each allele for a particular trait (Bb) Review: True-breeding organisms would be homozygous dominant OR recessive individuals. Hybrids would be heterozygous
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Show probabilities of future offspring.
8. Punnett Squares Show probabilities of future offspring. A monohybrid cross = cross between individuals that involve 1 contrasting trait.
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9. Monohybrid Crosses Examples
Ex. 1: One is heterozygous for round seeds x one with wrinkled seeds R r Phenotype/Genotype Chart R r r r r Phenotype Genotype(s) Round Wrinkled RR & Rr rr R r r r Plant #1’s genotype: Plant #2’s genotype: Rr rr Genotype probability:______________ Genotype ratio:___________________ Phenotype probability:_____________ Phenotype ratio:__________________
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B. Example 2 & 3: P & F1 cross for true-breed tall x true breed short
Phenotype Genotype(s) P cross F1 cross Tall TT, Tt Short tt Tt T t T t TT tt T T t Tt 25% pure tall 50% hybrid tall 25% pure short 100% Tall 100% Heterozygous (Homozygous x Homozygous) (Heterozygous x Heterozygous)
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End for today
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Complete and diagram the 3 types of monohybrid crosses below.
Round peas are dominant to wrinkled peas. Cross a homozygous dominant x homozygous recessive. Short plants are recessive to tall plants. Cross a homozygous recessive x heterozygous Green peas are dominant to yellow peas cross a heterozygous x heterozygous
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Round peas are dominant to wrinkled peas
Round peas are dominant to wrinkled peas. Cross a homozygous dominant x homozygous recessive. Phenotype Genotype(s)
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2. Short plants are recessive to tall plants
2. Short plants are recessive to tall plants. Cross a homozygous recessive x heterozygous Phenotype Genotype(s)
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3. Green peas are dominant to yellow peas cross a heterozygous x heterozygous
Phenotype Genotype(s)
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10. Test Crosses A cross of an individual of unknown genotype with an individual of known genotype.(has to be homozygous recessive) Results tells if unknown individual is heterozygous or homozygous Very important to breeders
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I. Beyond Mendel 1. Incomplete dominance
Offspring are intermediate between two parental phenotypes Neither allele is completely dominant over the other Both alleles influence phenotype 3 phenotypes
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Ex: Japanese Four o’clocks RR = red RR’ = pink R’R’ = white
All Pink 1 red : 2 pinks : 1 white
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2. Codominance Both alleles of a gene are expressed. A person with AB blood has both A and B antigens on their red blood cells. Neither allele is dominant or recessive
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P1 generation cross
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Both Brown and white expressed at the same time.
ROAN
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White & Red Mixed – RW (“roan”)
Ex: Red Coat - RR White Coat – WW White & Red Mixed – RW (“roan”) R R R W RW RW RW R W RR W RW RW RW WW All Roan – both red and white hair 1 red : 2 roan : 1 white
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3. Multiple Allele Traits are traits with 3 or more alleles; only get 2
1. ABO Blood group system; types – A, B, AB, O 2. IAIA =type A IAi = type A ii = type O IBIB= type B IBi = type B IAIB= type AB *A,B codominant *Both dominant to O
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IA IB IB IAIB IBIB IBIB IB IAIB
What are the possible blood types when a Person with AB blood and a person that is homozygous for B blood reproduce? Phenotype Genotype(s) Type A IAIA , IAi Type B IBIB , IBi Type AB IAIB Type O ii IA IB IB IAIB IBIB Type AB & B are possible IBIB IB IAIB
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IA IA IB IAIB IAIB IAIB IB IAIB
What are the possible blood types when a Person with homozygous A blood and a person that is homozygous for B blood reproduce? Phenotype Genotype(s) Type A IAIA , IAi Type B IBIB , IBi Type AB IAIB Type O ii IA IA IB IAIB IAIB Type AB only IAIB IB IAIB
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IB i IBi ii i i IBi ii What are the possible blood types when a
Person with B blood and a person with O blood reproduce? Phenotype Genotype(s) Type A IAIA , IAi Type B IBIB , IBi Type AB IAIB Type O ii IB i IBi ii i i IBi ii
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End of the notes today! Any questions?
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RrYy RrYy X RrYy Ry RY rY ry Law of Independent Assortment:
Genes for different traits are inherited independently R, r, Y, y go to sperm/egg independently of each other Can recombine in four ways: Ry RY RrYy rY ry
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3. Dihybrid Cross: A cross involving two pairs of contrasting traits
A = feathers C = crest Phenotypes Blue feathers Red feathers w/ Crest w/o Crest Genotypes aa AA, Aa CC, Cc cc Phenotypes Red feathers, w/ Crest Red feathers, w/o Crest Blue feathers, w/ Crest Blue feathers, w/o Crest Genotypes AACC, AACc, AaCC, AaCc AAcc, Aacc aaCC, aaCc aacc
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Example Cross P1: RRYY x rryy yellow, round green, wrinkled
(homozygous) (homozygous) RY RY RY RY Offspring are all heterozygous ry RrYy RrYy RrYy RrYy RrYy RrYy ry RrYy RrYy RrYy ry RrYy RrYy RrYy ry RrYy RrYy RrYy RrYy
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round, yellow: round, green : wrinkled, yellow: wrinkled ,green:
9 Round seeds are dominant to wrinkled and yellow is dominant to green. What are all the possible phenotypes? 3 round, yellow: round, green : wrinkled, yellow: wrinkled ,green: 3 RrYy X RrYy 1 Phenotypic Ratio is 9:3:3:1 RY Ry rY ry RY ry rY Ry RRYY RRYy RrYY RrYy RRyy Rryy rrYY rrYy rryy
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End of the notes today! Any questions?
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