Ch.11-2b Independent Assortment genetics

POINT > Define a dihybrid cross POINT > Describe Mendel’s dihybrid experiments POINT > Show how meiosis could lead to different allele combinations POINT > Use a Punnett square to predict genotypes and phenotypes from a dihybrid cross POINT > Define the Law of Independent Assortment

POINT > Define a dihybrid cross So far you have examined monohybrid crosses: crosses involving only one trait Mendel wondered if inheritance of one trait affected the inheritance of other traits, or if they all acted independently A dihybrid cross is a genetic cross that involves two traits Punnett squares are again useful in explaining what Mendel found

? P F1 POINT > Describe Mendel’s dihybrid experiments Ex. Mendel crossed plants purebred for yellow seeds and smooth seed coats with plants purebred for green seeds and wrinkled seed coats All the F1 had yellow seeds and smooth seeds coats P (YYRR) X (yyrr) ? F1 (YyRr)

POINT > Describe Mendel’s dihybrid experiments First generation (F1) plants self-pollinated: All trait combinations show up in the F2 F1 (YyRr) X (YyRr) ? F2

F2 POINT > Describe Mendel’s dihybrid experiments Every trait combination Mendel tried generated an F2 with the same proportions: 9 : 3 : 3 : 1 F2

WB CHECK: Which of the following is a monohybrid cross? a) Plant with black leaves X plant with pink flowers b) Plant with red berries and wrinkled seeds X plant with white berries and smooth seeds c) Fruit fly with 2 sets of wings X fruit fly with normal wings d) Fruit fly with white eyes and 8 legs X fruit fly with red eyes and 2 sets of wings

WB CHECK: Which of the following is a dihybrid cross? a) Plant with black leaves X plant with pink flowers b) Plant with red berries and wrinkled seeds X plant with white berries and smooth seeds c) Fruit fly with 2 sets of wings X fruit fly with normal wings d) Fruit fly with white eyes and 8 legs X fruit fly with red eyes and 2 sets of wings

POINT > Show how meiosis could lead to different allele combinations F1 plant meiosis (YyRr) Y y R r R Y y r R Y R Y y r y r

POINT > Show how meiosis could lead to different allele combinations F1 plant meiosis (YyRr) Y y r R Y r y R Y r Y r y R y R

R Y y r 25% 25% Y R y r Y r y R 25% 25% Y r y R Expected gametes if traits move independently of each other

POINT > Use a Punnett square to predict genotypes and phenotypes from a dihybrid cross A Punnett square to examine the inheritance of two different traits requires a 4x4 grid:

Y y R r yr YR yR Yr To generate gametes use FOIL: POINT > Use a Punnett square to predict genotypes and phenotypes from a dihybrid cross To generate gametes use FOIL: Each gamete must have only one letter from each trait!! Y y R r R Y Y r y R y r yr YR Yr yR

WB CHECK: Show the 4 possible gametes produced by a raccoon heterozygous for tail length (Tt) and heterozygous for ear tufts (Ee): TE Te tE te

YR Yr yR yr YR Yr yR yr YYRR YYRr YyRR YyRr YYRr YYrr YyRr Yyrr YyRR POINT > Use a Punnett square to predict genotypes and phenotypes from a dihybrid cross YR Yr yR yr YR YYRR YYRr YyRR YyRr Each gamete must have only one letter from each trait!! Yr YYRr YYrr YyRr Yyrr yR YyRR YyRr yyRR yyRr yr YyRr Yyrr yyRr yyrr

YR Yr yR yr YR Yr yR yr YYRR YYRr YyRR YyRr YYRr YYrr YyRr Yyrr YyRR POINT > Use a Punnett square to predict genotypes and phenotypes from a dihybrid cross YR Yr yR yr Genotypes YR YYRR YYRr YyRR YyRr YYRR 1 YYRr 2 Yr YYrr 1 YYRr YYrr YyRr Yyrr YyRR 2 YyRr 4 yR Yyrr 2 YyRR YyRr yyRR yyRr yyRR 1 yyRr 2 yr yyrr 1 YyRr Yyrr yyRr yyrr

YR Yr yR yr YR Yr yR yr YYRR YYRr YyRR YyRr YYRr YYrr YyRr Yyrr YyRR POINT > Use a Punnett square to predict genotypes and phenotypes from a dihybrid cross YR Yr yR yr YR YYRR YYRr YyRR YyRr Yr YYRr YYrr YyRr Yyrr yR YyRR YyRr yyRR yyRr yr YyRr Yyrr yyRr yyrr

YR Yr yR yr YR Yr yR yr Phenotypes Yellow, Round 9 Yellow, Wrinkled 3 POINT > Use a Punnett square to predict genotypes and phenotypes from a dihybrid cross YR Yr yR yr Phenotypes YR Yellow, Round 9 Yr Yellow, Wrinkled 3 yR Green, Round 3 Green, Wrinkled 1 yr

POINT > Define the Law of Independent Assortment Genes for different traits segregate independently during gamete formation (meiosis) This helps explain the amazing amount of variation in many species!

Homework Read pages 313-318 Punnett Squares Practice 1 Finish Assess p. 318 and any other missing homework