Presentation on theme: "Fundamentals of Genetics. I. Introduction to Genetics 1. Gregor Mendel - “Father of Genetics” Austrian monk, teacher, scientist, gardener Formulated basic."— Presentation transcript:
I. Introduction to Genetics 1. Gregor Mendel - “Father of Genetics” Austrian monk, teacher, scientist, gardener Formulated basic laws of heredity in the early 1860s
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
5. Mendel cross-pollinated plants P = parental generation F 1 = first-generation (sons/daughters) F 2 =second-generation
6. Principle of Dominance and Recessiveness F 1 plants resembled only one of the parents F 1 hybrids contained two different factors (alleles) for each trait one dominant; (masks recessive); one recessive; (seems to disappear)
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.
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
II. Chromosomes, Genes, & Genetic Crosses 1.Homologous Chromosomes contain genes (locations on DNA for traits) for the same traits 2.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.
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
8. Punnett Squares Show probabilities of future offspring. A monohybrid cross = cross between individuals that involve 1 contrasting trait.
9. Monohybrid Crosses Examples Ex. 1: One is heterozygous for round seeds x one with wrinkled seeds Phenotype/Genotype Chart Genotype probability:______________ Genotype ratio:___________________ Phenotype probability:_____________ Phenotype ratio:__________________ Phenotype Genotype(s) Round Wrinkled RR & Rr rr Plant #1’s genotype: Plant #2’s genotype: Rr rr r r Rr Rr Rr rr rr
B. Example 2 & 3: P & F 1 cross for true-breed tall x true breed short P cross F 1 crossT t t Tt TtTt TT Tttt 100% Tall 100% Heterozygous 25% pure tall 50% hybrid tall 25% pure short (Homozygous x Homozygous) (Heterozygous x Heterozygous) Phenotype Genotype(s) Tall Short TT, Tt tt
Complete and diagram the 3 types of monohybrid crosses below. 1.Round peas are dominant to wrinkled peas. Cross a homozygous dominant x homozygous recessive. 2.Short plants are recessive to tall plants. Cross a homozygous recessive x heterozygous 3.Green peas are dominant to yellow peas cross a heterozygous x heterozygous
1.Round peas are dominant to wrinkled peas. Cross a homozygous dominant x homozygous recessive. Phenotype Genotype(s)
2. Short plants are recessive to tall plants. Cross a homozygous recessive x heterozygous Phenotype Genotype(s)
3. Green peas are dominant to yellow peas cross a heterozygous x heterozygous Phenotype Genotype(s)
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
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
Ex: Japanese Four o’clocks RR = redRR’ = pink R’R’ = white RR R’ RR’ R R’ RRRR’ R’R’ All Pink1 red : 2 pinks : 1 white
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
Brown WHITE ROAN Both Brown and white expressed at the same time.
Ex: Red Coat - RR White Coat – WW White & Red Mixed – RW (“roan”) R WWWW R W R WR W RR RW WW All Roan – both red and white hair 1 red : 2 roan : 1 white
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. I A I A =type A I A i = type A ii = type O I B I B = type B I B i = type B I A I B = type AB *A,B codominant *Both dominant to O
What are the possible blood types when a Phenotype Genotype(s) Person with AB blood and a person that is homozygous for B blood reproduce? Type A Type B Type AB Type O I A I A, I A i I B I B, I B i IAIBIAIB ii IAIA IBIB IBIB IBIB IAIBIAIB IAIBIAIB IBIBIBIB IBIBIBIB Type AB & B are possible
What are the possible blood types when a Phenotype Genotype(s) Person with homozygous A blood and a person that is homozygous for B blood reproduce? Type B Type A Type AB Type O I A I A, I A i I B I B, I B i IAIBIAIB ii IAIA IAIA IBIB IBIB IAIBIAIB IAIBIAIB IAIBIAIB IAIBIAIB Type AB only
What are the possible blood types when a Phenotype Genotype(s) Person with B blood and a person with O blood reproduce? Type B Type A Type AB Type O I A I A, I A i I B I B, I B i IAIBIAIB ii IBIB i i i IBiIBi IBiIBi
RrYy X RrYy 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: RrYy
3. Dihybrid Cross: A cross involving two pairs of contrasting traits A = feathers C = crest Phenotypes Blue feathers Red feathers Phenotypes w/ Crest w/o Crest Genotypes aa AA, Aa Genotypes 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
Example Cross P 1 : RRYY x rryy yellow, round green, wrinkled(homozygous) RYRYRYRY ryry ryry RrYyRrYyRrYy Offspring are all heterozygous RY ryry ryry RrYy
round, yellow: round, green : wrinkled, yellow: wrinkled,green: RY RyrYry RY ry rY Ry RRYYRRYyRrYYRrYy RRYyRrYy RrYYRrYy RRyyRryy rrYYrrYy rryy RrYy X RrYy Phenotypic Ratio is 9:3:3:1 9 3 3 1 Round seeds are dominant to wrinkled and yellow is dominant to green. What are all the possible phenotypes?