Studying Heredity Chapter 8 Section 8-3. Objectives for section 8-3 Predict results of genetic crosses w/Punnett Square Predict results of genetic crosses
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Studying HeredityChapter 8 Section 8-3
Objectives for section 8-3Predict results of genetic crosses w/Punnett SquareDescribe how a testcross can be used to determine genotypeDefine & analyze a simple pedigreePG. 170
Punnett Squarepredicts possible outcomes of genetic crosses Inventor Reginald Punnett
1. Assign letters for traits2. Determine parents genotypes4. Fill in each box of the Punnett square 3. Write genotypes across top & side 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 recessiveBreeders need to know if organism- heterozygous/ homozygous dominant for a characterWhy?
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 traitsCross 2 pea plants heterozygous for seed shape AND seed color1. R=round r=wrinkled AND Y=yellow y=green2. Parents genotypesa. RrYy x RrYy3. Possible Gametes??a. RY, Ry, rY, ry
Typical Dihybrid Cross
4. Phenotypic ratio9 round, yellow3 round, green3 wrinkled, yellow1 wrinkled greenTypical dihybrid cross ratio: 9:3:3:1
Monohybrid vs. Dihybrid CrossMonohybrid: 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 cropsB. Improve domestic animalsC. Determine risk for genetic disordersD. Predict expected results of genotypes or phenotypes
Probability likelihood that a specific event will occurA. Expressed in words, decimals, fractions, or percentagesB. Probability= # of 1 kind of possible outcome/total # of all possible outcomesC. 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 generationsHelps in tracking genetic disordersColorblindness Pedigree
What is determined from a pedigree?Autosomal: gene will appear in both sexes equally Sex-linked: allele located only on the X chromosome & are recessive a. Males carrying recessive allele on X chromosome exhibit sex-linked characterWhy??b. Females-less chance of exhibiting sex-linked conditionWhy??
Pedigree for the Albino Trait Pedigree for HemophiliaSex linked!! Only affectedautosomal
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 allele6. Homozygous recessive: phenotype shows the recessive allele
Can 2 people who are heterozygouscarriers of a recessive mutation have children with the mutation??
Hemophilia-the Royal disease1 in 10,000 1 in 100,000,000