Genetics The study of heredity • Genes are found on chromosomes. Chromosomes are made up of DNA. Alleles: Different forms of a gene. Dominant: If the dominant allele (gene) is present, the organism will show that trait. Recessive: Trait will be exhibited only if organism does not have dominant allele or is pure for recessive trait. Gregor Mendel (1822-1884) An Austrian monk who cultivated and studied garden pea plants. His studies produced the basic concepts of heredity. Genotype: The Allele combination, heterozygous (hybrid) or homozygous (gg, GG, or Gg). Phenotype: The physical characteristic displayed (green or yellow). Trait Dominant Allele Recessive Allele Possible Genotype Possible Phenotypes Seed Color G (green) g (yellow) GG Homozygous Gg Heterozygous gg Green Flower Color P (purple) p (white) PP Homozygous Pp Heterozygous pp Green Yellow Purple Purple white Why Pea Plants? •Many observable contrasting traits. •Easy to grow. •Short time between one generation and the next. Structure of flower Cross Pollination Punnett Square In Pea plants Green pods (G) are dominant over yellow (g) pods. Genotype GG homozygous Gg heterozygous gg Phenotype Green Pod Green Pod Yellow Pod P Cross : GG x gg g Possible Gametes : ____ ____ X ____ ____ g G Gg Gg Green Pod Green Pod G Gg Gg Green Pod Green Pod F1 Genotypic ratio: F1 Phenotypic ratio: F1 Cross: Gg x Gg Possible Gametes: ____ ____ X ____ ____ F2 Genotypic ratio: F2 Phenotypic ratio: In mice black is dominant over white; B – black, b- white, BB homozygous black, Bb heterozygous black, bb recessive white Cross two heterozygous black mice, Bb x Bb Cross : Bb x Bb Possible Gametes : ____ ____ X ____ ____ Genotypic ratio: Phenotypic ratio: Test Cross Is this back mouse homozygous black BB or heterozygous black Bb? One way to find out is to do a Test Cross. Cross this black mouse with the recessive white bb. BB x bb Bb x bb If any of the offspring produced are white or show the recessive trait, then the black mouse had to be heterozygous Bb. If all of the offspring produced are black, you cannot be 100% positive that the black mouse is homozygous BB because the inheritance of a an allele is a 50/50 chance. Monohybrid Cross: Rr x Rr Dihybrid Cross: RrYy x RrYy Dihybrid Cross 2 traits; plant height and seed color P Cross: TTRR ( pure tall & round) x ttrr (pure short & wrikled) _____ _____ ______ _____ _____ _____ _____ _____ F1 Cross TtRr (hybrid tall & round) x TtRr (hybrid tall & round) _____ _____ _____ _____ _____ _____ _____ _____ F2 Genotype F2 Phenotype Incomplete Dominance Genotype RR WW RW Phenotype Red flower White flower Pink flower P Cross: RR x WW W R R W RW RW Pink Pink RW RW Pink Pink F1 Genotype: 100% RW F1 Phenotype: 100% Pink flower Co dominance Genotype RR WW RW Phenotype Red cow White cow Roan cow P Cross: RR x WW R R W RW W RW Roan Roan RW RW Roan Roan Genotype of F1 offspring: 100% RW Phenotype of F1 offspring: 100% Roan Multiple Alleles Blood Types Allele Antigen on RBC IA A IB B i none Genotype IA IA homozygous IA i heterozygous IB IB homozygous IB i heterozygous IA IB ii Phenotype Type A Type A Type B Type B Type AB Type O Crosses Involving Multiple Alleles Cross: a man who is homozygous for blood type A with a woman who is homozygous blood type B. IA IA x IB IB IB IA IA IB IA IB IA IB Type AB Type AB IA IB IA IB Type AB Cross: a man who is heterozygous for blood type A with a woman who is blood type O. IA i x i i Type AB i i IA IA i IA i Type A Type A i ii ii Type O Type O Sex Determination Sex Linked Traits Traits located on the X chromosome Genotype XX XcX XcXc XY XcY Cross: A normal male with a carrier female. XY x XcX X Xc X Xc X Phenotype Normal Female Carrier Female Colorblind Female Normal Male Colorblind Male Cross: A colorblind male with a carrier female. XcY x XcX Y X cY Carrier Female Colorblind Male XX XY Normal Female Normal Male Xc X Xc Y Xc Xc Xc Y Colorblind Female Colorblind male Xc X XY Carrier Female Normal Male Human Pedigree Key Human Pedigree Autosomal Recessive Human Pedigree Autosomal Dominant Human Pedigree Sex linked Recessive http://www.zerobio.com/drag_gr11/pedigree/pedigree4.htm Chromosomes Karyotype Female XX Male XY