2 History Gregor Mendel: “Father of Genetics” Austrian Monk (1822-1884) Published the results of scientific research on Garden Peas (Pisium sativum) in 1865.Why study peas?Great natural variation- stem length, seed color, pod shape ,pod color, small, edible, easy to grow, many offspring, easy to cross fertilize
3 Useful Terms Trait: characteristic of an organism. Gene: piece of DNA that codes for a protein.Allele: different forms of a gene.Genotype: The allele combination of an individual.Phenotype: The visible characteristics that result from a genotype.
4 Chromosomes and Human Genetics Human ChromosomesTypesSex Chromosomes – 1 pair – carry the genes that determine male and female features (also some non-sex traits)X and Y do not look alike but behave as a homologous pair at meiosisXX = female, XY = maleAutosomes – non-sex chromosomes (22 pairs) – genes are unrelated to sex determination
5 PUNNETT SQUAREMethod for determining possible allele combination for the offspringGametes outsideOffspring Inside
7 One Example of Mendel’s Work TallxDwarfPhenotypePDDddGenotypeHomozygousDominantHomozygousRecessiveAll TallClearly Tall is Inherited…What happened to Dwarf?F1DdTall is dominant to DwarfUse D/d rather than T/t for symbolic logicHeterozygousF1 x F1 = F2possible gametesPunnett Square:Dd3/4 Tall1/4 DwarfF2DTallDDTallDdpossible gametesdTallDdDwarfddDwarf is not missing…just masked as “recessive” in a diploid state… there IS a female contribution.
8 Sample ProblemIn hamsters, white fur color (W) is dominant to brown fur color (w). If you cross a heterozygous female with white fur color (Ww) with a male that has brown fur (ww), what genotypes and phenotypes would you see and in what ratios?
11 Genetics After Mendel P F1 F2 Red Yellow x PRPR PYPY All Orange PRPY After 1900 several scientists tried to replicate Mendel’s crosses using other species including snapdragon.Genetics After MendelRedYellowPxPRPRPYPYWhen these alleles go walking, they both do some talking (codominance)!OK, so we cannot use R/r nor Y/y so we pick a third letter…P for the petal color gene.Notice: we do NOT mix R/Y or r/y!All OrangeF1PRPYF1 x F1 = F2possible gametesPunnett Square:PRPYF2PRRedPRPROrangePRPYThis F2 will NOT have a 3:1 ratio of phenotypes.Instead it shows a 1:2:1 ratio!The exception here proves the rule.possible gametesPYOrangePRPYYellowPYPY
12 Sample ProblemIn horses, black and white coat colors are codominant. Heterozygous horses have gray coats.Black horse genotype: HBHBWhite horse genotype: HWHWGray horse genotype: HBHWWhat would be the possible genotypes and phenotypes of the following crosses?Black x WhiteGray x Gray
14 Blood Types Blood Type: A B AB O Genotype IAIA , IAi IBIB , IBi IAIB
15 Try TheseIf a male is homozygous for blood type B and a female is heterozygous for blood type A, what are the possible blood types in the offspring?
16 Is it possible for a child with Type O blood to be born to a mother who is type AB? Why or why not?
17 Chromosomes and Human Genetics Human ChromosomesTypesSex Chromosomes – 1 pair – carry the genes that determine male and female features (also some non-sex traits)X and Y do not look alike but behave as a homologous pair at meiosisXX = female, XY = maleAutosomes – non-sex chromosomes (22 pairs) – genes are unrelated to sex determination
19 II. Gene LocationLinked – Linkage Groups – genes located so close together on a chromosome that the traits always seem to appear togetherEx. Red hair and frecklesEx. Colorblindness and HemophiliaX X
20 Sex-linked Traits – genes on the sex chromosomes Expression of certain genes often appears more in one sex than the otherMales require only one copy of a gene since they only have one X chromosomeSee Royal Families of Europe PedigreeEx. Eye color in fruit flies, hemophilia, color-blindness
23 X-Linked/Sex Linkage – do not write Genes present on the X chromosome exhibit unique patterns of inheritance due to the presence of only one X chromosome in males.X-linked disorders show up rarely in femalesX linked disorders show up in males whose mothers were carriers (heterozygotes)
24 Practice Sex-linked Problems…. What will the result of mating between a normal (non-carrier) female and a hemophiliac male?
25 A female carrier who is heterozygous for the recessive, sex-linked trait causing red-green colorblindness, marries a normal male. What proportions of their MALE progeny will have red-green colorblindness?
26 Hemophilia is inherited as an X-linked recessive Hemophilia is inherited as an X-linked recessive. A woman has a brother with this defect and a mother and father who are phenotypically normal. What is the probability that this woman will be a carrier if she herself is phenotypically normal?
27 C. Gene InteractionsPolygenetic trait – many genes influence a single trait (ex. Height, intelligence)Pleiotropic effect – one gene having many effects (ex. Gene to make testosterone)
28 Pleiotropy?Expression of a single gene has multiple phenotypic effectsMarfan Syndrome – abnormal gene that makes fibrillin (important in connective tissues)
29 III. Genetic AnalysisKaryotype – visualized chromosomes stained, squashed, and photographed at metaphase- They are characteristic of the species or individual
30 B. Pedigree – chart showing family relationships (see worksheet)
31 Pedigree AnalysisMethod of tracking a trait through generations within a family.Good method of tracking sex-linked traits as well as autosomal traits.
35 Autosomal Dominant Pedigree Autosomal dominant traits do not skip a generationAutosomal dominant traits do not show gender bias
36 Autosomal Recessive Pedigree Autosomal recessive traits skip a generationAutosomal recessive traits do not show gender bias
37 IV. Non-Mendelian Genetics Incomplete Dominance – blended inheritanceNeither form of the gene is able to mask the otherEx. Snap dragon petal colorR1R1 – REDR1R2 – PINKR2R2 - WHITE
38 Incomplete Dominance Neither allele is dominant Heterozygotes are a blend of homozygous phenotypes = no distinct expression of either allele
39 Try theseIn a plant species, if the B1 allele (blue flowers) and the B2 allele (white flowers) are incompletely dominant (B1 B2 is light blue), what offspring ratio is expected in a cross between a blue-flowered plant and a white-flowered plant?
40 What would be the phenotypic ratio of the flowers produced by a cross between two light blue flowers?
41 2. Codominance No dominance and both alleles are completely expressed Ex. Cat colorC1C1 – TanC1C2 – Tabby (black and tan spotted)C2C2 - Black
42 Try TheseCattle can be red (RR = all red hairs), white (WW = all white hairs), or roan (RW = red & white hairs together.Predict the phenotypic ratios of offspring when a homozygous white cow is crossed with a roan bull.
43 What should the genotypes & phenotypes for parent cattle be if a farmer wanted only cattle with red fur?
44 A cross between a black cat & a tan cat produces a tabby pattern (black & tan fur together). What pattern of inheritance does this illustrate?What percent of kittens would have tan fur if a tabby cat is crossed with a black cat?
45 3. Multiple Alleles More than 2 alleles for one trait Ex. Eye color, hair color, blood type, guinea pig fur colorABO blood groupsEach individual is A, B, AB, or O phenotypePhenotype controlled by marker on RBCIA and IB alleles are dominant to the i alleleIA and IB alleles are codominant to each other
46 Blood Types Blood Type: A B AB O Genotype IAIA , IAi IBIB , IBi IAIB
48 Try TheseIf a male is homozygous for blood type B and a female is heterozygous for blood type A, what are the possible blood types in the offspring?
49 Is it possible for a child with Type O blood to be born to a mother who is type AB? Why or why not?
50 A child is type AB. His biological mother is also type AB A child is type AB. His biological mother is also type AB. What are the possible phenotypes of his biological father?
51 Recessive can be common! Human hair color follows a similar pattern:Alleles: HBn = brown HBd = blonde hR = red hbk = blackHBnHBn = dark brownHBnHBd = sandy brownHBnhR = auburnHBnhbk = dark brownHBdHBd = blondeHBdhR = strawberry blondeHBdhbk = blondehRhR = redhRhbk = redhbkhbk = blackDominant does NOT mean frequent!Recessive can be common!