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7.4 Two trait Crosses

7.4 Two trait Crosses. Lesson Objectives. Students will be able to: Predict offspring inheritance of two traits. Gametes. Gametes have 1 allele for each gene Alleles for each trait can be combined in many different combinations in the gametes For example –

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7.4 Two trait Crosses

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  1. 7.4 Two trait Crosses

  2. Lesson Objectives • Students will be able to: • Predict offspring inheritance of two traits

  3. Gametes • Gametes have 1 allele for each gene • Alleles for each trait can be combined in many different combinations in the gametes • For example – • Take 1 letter from each word; how many different arrangements? THE CAT

  4. Two Traits • If A = tall; a = short & B = blue; b = white • What is the phenotype of: • AaBB • aabb • AAbb • aaBb

  5. Dihybrid Crosses: • Dihybrid = an individual that is heterozygous for two traits • Example: AaBb

  6. Dihybrid Crosses • Consider two genes in peas: • Pea color: Y (yellow) & y (green) • Pea shape: R (round) & r (wrinkled) • Parent genotype: YyRr • Parent phenotype: yellow & round • What gametes will this parent make? • REMEMBER: the gametes must contain one allele for each gene • YR, Yr, yR, yr

  7. Dihybrid Crosses; Y=yellow y=green; R = round r = wrinkled • Practice Cross: YyRr x YyRr • Gametes from each parent: YR, Yr, yR, yr YR Yr yR yr YYRR YR YYRr YrRR YyRr Yr YYRr YYrr YyRr Yyrr YyRR yyRR yyRr yR YyRr yr YyRr Yyrr yyRr yyrr

  8. Dihybrid Crosses; Y=yellow y=green; R = round r = wrinkled • How many genotypes are… • Yellow & round: 9 • Yellow & wrinkled: 3 • Green & round: 3 • Green & wrinkled: • Phenotypic ratio?

  9. Dihybrid Crosses • Two dihybrid parents will always make a phenotypic ratio… • Dom, Dom : Dom, rec : rec, Dom : rec, rec 9 : 3 : 3 : 1

  10. Dihybrid Crosses – Let’s Practice • L = long fur; l = short fur • P = polka dots; p = solid color • Parents: LlPp x LlPp • What proportion of offspring will have… • Long, polka dotted fur? • Long, solid fur? • Short, polka dotted fur? • Short, solid fur?

  11. Other two trait crosses • TtPPx TTPP – NOT dihybrid • Gametes from Parent #1: TP, tP • Gametes from Parents #2: Tp • Possible genotypes & phenotypes of the offspring? • A male rabbit with the genotype GGbb is crossed with a female rabbit with the genotype ggBb. Determine the phenotypes and proportions in the offspring. • How many out of 16 have grey fur & black eyes? • How many out of 16 have grey fur & red eyes? • How many out of 16 have white fur & black eyes? • How many out of 16 have white fur & red eyes?

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