1. Dihybrid Crosses
Biology
Mrs. Harper
1/23/18

2. January 23, 2018 Begin working on Do Now
Genetics and Heredity continued…

3. Do Now 11/12/15 Tall Tall short FF or Ff ff
1. Give an example of each of the following genotypes: homozygous dominant, homozygous recessive and heterozygous.
2. What is the difference between dominant and recessive?
3. Circle the recessive alleles.
A c s D f Y e u L X w b O
4. Tall is dominant to short. What would be the phenotypes of the following genotypes?
TT___________________ Tt___________________ tt_____________________
5. Freckles are dominant to no freckles. What would be the genotypes of the following phenotypes?
Freckles genotypes:______________________ No freckles genotype_________
6. Large noses are dominant to small. A heterozygous large nosed man marries a recessive small nosed female. What is the probability that their babies will have a large nose? What is the probability the babies will have a small nose?
HH, hh, Hh
Tall
Tall
short
FF or Ff ff

4. Punnett Square Practice
Large noses are dominant to small. A heterozygous large nosed man marries a recessive small nosed female.
What is the probability that their babies will have a large nose?
What is the probability the babies will have a small nose?
Large- dominant
Small- recessive

5. Punnett Square Practice
Brown hair is dominant to blonde hair. Cross a heterozygous brown haired male and a heterozygous brown haired female.
What is the probability that the babies will have brown hair?
What is the probability that they will have blonde hair?
Brown- dominant
Blonde- recessive

6. Dihybrid Crosses: Involves 2 Traits
Dihybrid Cross: a cross that shows the possible offspring for two traits (ex: color and texture)
(How does this work? Do the alleles just travel together? )
Law of Independent Assortment: Each pair of alleles separates independently during the formation of the sex cells (gametes)

7. How to Solve a Dihybrid Cross:
Fur Color: B: Black b: White
Coat Texture: R: Rough r: Smooth
We will cross a heterozygous individual for both traits with another heterozygous individual.
Step 1: Determine each parent’s genotype:
Parent 1 ___________ x Parent 2 ___________

8. BbRr x BbRr
Step 2: Determine gametes for each parent (1st letter pairs with 3rd then 1st letter pairs with 4th letter)
Following that, 2nd letter pairs with 3rd then 2nd letter pairs w/ 4th letter)
Parent 1: BbRr ____ ____ ____ ____
Parent 2: BbRr ____ ____ ____ ____

9. BR Br bR br BR BBRR BBRr BbRR BbRr BBRr BBrr BbRr Bbrr Br BbRR BbRr
Step 3: Place all possible gametes for one parent on the top and all gametes for other parent on the side of Punnett Square & perform the cross. BR Br bR br BR
BBRR
BBRr
BbRR
BbRr
BBRr
BBrr
BbRr
Bbrr Br
BbRR
BbRr
bbRR
bbRr bR
BbRr
Bbrr
bbRr
bbrr br

10. Step 4: Find all possible genotypes & phenotype combinations.
How many are black and rough?
How many are black and smooth?
How many are white and rough?
How many are white and smooth?
What is the phenotypic ratio? 9 3 3 1
9:3:3:1

11. Assignment Complete the dihybrid crosses practice.
When finished, raise your hand and I will give you the extra monohybrid cross worksheet and a review sheet for your quiz tomorrow.
Unfinished classwork is homework