Transcript 8-3 notes
Studying Heredity Chapter 8 Section 8-3 Objectives for section 8-3 Predict results of genetic crosses w/Punnett Square Describe how a testcross can be used to determine genotype Define & analyze a simple pedigree PG. 170 Punnett Square • predicts possible outcomes of genetic crosses Inventor– Reginald Punnett Monohybrid Cross 1. Assign letters for traits 2. Determine parents’ genotypes 3. Write genotypes across top & side 4. Fill in each box of the Punnett square 5. State genotype and phenotype A heterozygous dimpled female marries a heterozygous male. What are the possible outcomes of their children? D Test cross: dominant phenotype/unknown genotype (x) w/ homozygous recessive Breeders need to know if organismheterozygous/ homozygous dominant for a character Why? EX: A plant w/ yellow seeds & unknown genotype (Y?) is test crossed with a plant that has green seeds (yy). V. Dihybrid Crosses =2 contrasting traits Cross 2 pea plants heterozygous for seed shape AND seed color 1. R=round r=wrinkled AND Y=yellow y=green 2. Parents’ genotypes a. RrYy x RrYy 3. Possible Gametes?? a. RY, Ry, rY, ry Typical Dihybrid Cross 4. Phenotypic ratio 9 round, yellow 3 round, green 3 wrinkled, yellow 1 wrinkled green Typical dihybrid cross ratio: 9:3:3:1 Monohybrid vs. Dihybrid Cross Monohybrid: involves one trait with a phenotypic ratio for the F2 generation of 3:1 Dihybrid: involves two traits with a phenotypic ratio for the F2 generation of 9:3:3:1 Why use Punnett Squares? A. Improve crops B. Improve domestic animals C. Determine risk for genetic disorders D. Predict expected results of genotypes or phenotypes Probability –likelihood that a specific event will occur A. Expressed in words, decimals, fractions, or percentages B. Probability= # of 1 kind of possible outcome/total # of all possible outcomes C. Both parents must be considered when calculating probability D. To find probability, multiply the separate probabilities of the two events Pedigree: family history-shows a trait inherited over several generations Helps in tracking genetic disorders ♀ Colorblindness Pedigree ♂ What is determined from a pedigree? 1. Autosomal: gene will appear in both sexes equally 2. Sex-linked: allele located only on the X chromosome & are recessive a. Males carrying recessive allele on X chromosome exhibit sex-linked character…Why?? b. Females-less chance of exhibiting sexlinked condition…Why?? Pedigree for the Albino Trait ♀ ♂ autosomal Pedigree for Hemophilia Sex linked!! Only ♂ affected 3. Autosomal Dominant: every individual w/condition has a parent w/condition 4. Recessive: individual w/ condition can have 1, 2, or neither parent exhibit the condition 5. Homozygous dominant or heterozygous: phenotype will show the dominant allele 6. Homozygous recessive: phenotype shows the recessive allele Can 2 people who are heterozygous carriers of a recessive mutation have children with the mutation?? Hemophilia-the Royal disease 1 in 10,000 ♂ 1 in 100,000,000 ♀