Presentation on theme: "Today’s Objectives TSW employ the four primary rules for solving genetics problems. TSW successfully solve genetics crosses involving one and two alleles."— Presentation transcript:
1 Today’s ObjectivesTSW employ the four primary rules for solving genetics problems.TSW successfully solve genetics crosses involving one and two alleles.TSW successfully solve monohybrid and dihybrid crosses using the Punnett Square.
3 Steps for Solving a Genetics Problem: Trait – dominant = A (AA or Aa) Trait – recessive = a (aa)___________ x ___________Punnett SquareAnswer questions based on results from Punnett Square____
4 Monohybrid Crosses Cross that involves one pair of contrasting traits Solve using Punnett SquareSample problems:Rr x rrRR x rrRr x RrRr x RR
5 Let’s Solve TogetherShort hair (L) is dominant to long hair (l) in mice. What is the genotype and phenotype ratio of a heterozygous short-haired mouse crossed with a long-haired mouse?
6 Example 1: MonohybridShort hair = dominant = L (LL or Ll) long hair = recssive = lLl x ll (heterozygote parent = Ll)Punnett Square:Genotype ratio: ½ Ll: ½ llPhenotype ratio: ½ short hair: ½ long hairLlLlll
7 Dihybrid Crosses Involves two pairs of contrasting traits Pea shape and pea colorCoat length and coat color in rodentsPlant height and flower color
8 Let’s Solve TogetherIn guinea pigs, the allele for short hair (S) is dominant to long hair (s), and the allele for black hair (B) is dominant over the allele for brown hair (b). What is the probable offspring phenotype ratio for a cross involving two parents that are heterozygotes for both traits?
9 Example 2: DihybridShort hair = dominant = SS or Ss Long Hair = recessive = ss Black coat = dominant = BB or Bb Brown coat = recessive = bbSsBb x SsBb (gametes done by the FOIL method)SB, Sb, sB, sb and SB, Sb, sB, sb
10 Example 2: Punnett Square SBSbsBsbSSBBSSBbSsBBSsBbSSbbSsbbssBBssBbssbb
11 Example 2: Answer the Question What is the probable offspring phenotype ratio for a cross involving two parents that are heterozygotes for both traits?9/16 Black, short coats3/16 Black, long coats3/16 Brown, short coats1/16 Brown, long coats
12 Other Types of Heredity Patterns Incomplete Dominance – blending of traits in heterozygote.Pink flowersRR = redRr = pinkrr = white
13 Other Types of Heredity Patterns Codominance – can see both alleles at the same time.Roan coats in horsesSome white hairs, some red hairs
14 Multiple Alleles Blood Types in Humans Single gene, but four phenotypesType A can be AA or AoType B can be BB or BoType AB only AB (codominant pattern here)Type O only oo (both recessive)All 3 blood types are dominant to O
15 Continuous Variation Multiple genes are involved Examples Eye color Skin colorHair color
16 Sex-linked Genes Present on the X chromosome More common in males When would a female have this phenotype?Examples:BaldnessHemophilia
17 Some Human Genetic Disorders Of Interest Cystic FibrosisSickle-cell AnemiaTay-Sachs DiseasePhenylketonuria (PKU)HemophiliaHuntington’s DiseaseMuscular Dystrophy