Ch.11-2b Independent Assortment

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

? Ex. Mendel crossed plants purebred for yellow seeds and smooth seed coats with plants purebred for green seeds and wrinkled seed coats All the F 1 had yellow seeds and smooth seeds coats (YYRR)(yyrr) (YyRr) P F1F1 X POINT > Describe Mendel’s dihybrid experiments

? First generation (F 1 ) plants self-pollinated: All trait combinations show up in the F 2 (YyRr) F1F1 F2F2 X POINT > Describe Mendel’s dihybrid experiments

F2F2 Every trait combination Mendel tried generated an F 2 with the same proportions: 9 : 3 : 3 : 1

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

YYyy RRrr RR YY yy rr R Y R Yy r y r POINT > Show how meiosis could lead to different allele combinations F 1 plant meiosis (YyRr)

YYyy RR rr YY rr yy RR y R y R Y r Y r POINT > Show how meiosis could lead to different allele combinations F 1 plant meiosis (YyRr)

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

A Punnett square to examine the inheritance of two different traits requires a 4x4 grid:

To generate gametes use FOIL: Each gamete must have only one letter from each trait!! Y y R r YRYryRyr R Y Y r y R y r

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

YRYryRyr YR Yr yR yr YYRRYYRrYyRRYyRr YYRrYYrrYyRrYyrr YyRRYyRryyRRyyRr YyRrYyrryyRryyrr Each gamete must have only one letter from each trait!! POINT > Use a Punnett square to predict genotypes and phenotypes from a dihybrid cross

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

YRYryRyr YR Yr yR yr YYRRYYRrYyRRYyRr YYRrYYrrYyRrYyrr YyRRYyRryyRRyyRr YyRrYyrryyRryyrr POINT > Use a Punnett square to predict genotypes and phenotypes from a dihybrid cross

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

Law of Independent Assortment: Genes for different traits segregate independently during gamete formation (meiosis) Helps explain great amount of variation in many species

Read pages Finish Assess p. 318 and any other missing homework Complete your Exam 1 Study Guide