1

Friday, December 14

Bell Work:

If red is dominant to white in flowers, how do we get pink ones?

2

• We have discussed human traits that have two completely different phenotypes (physical appearances)

• We’ve also traced the possible combinations of alleles that a child may inherit through punnett squares.

• Genotype (combination of alleles ex: Pp, tt, etc.)

Review

3

• Remember: Mendelian inheritance is controlled by dominant and recessive paired alleles.

• In these cases heterozygous and homozygous dominant individuals both had the same phenotype.

• HOWEVER…This is not always the case

Not as simple as Mendel thought…

4

Incomplete Dominance: ONE ALLELE IS NOT COMPLETELY DOMINANT OVER THE OTHER; CAUSES A BLENDING OF TRAITS

Example of Incomplete Dominance: Four o’clock flowers, snap dragons

Red + White = Pink

5

Example 2:

When green betta fish (B1B1) are crossed with a steel blue betta fish (B2B2) all the offspring have the heterozygous genotype (B1B2).

These offspring will be royal blue in color.

Practice Problem: What is the phenotypic ratio with two Royal Blue betta fish are crossed?

6

Practice Problems:

The petal color of snapdragons is inherited by incomplete dominance. Plants with R1R1 genes have red flowers. Plants with R2R2

genes have white flowers. Plants with R1R2 genes have pink flowers.

1. Joey planted snapdragons in his garden. All the seeds came from one set of parent plants. When the flowers bloomed, Joey saw that all of his flowers were pink. What were the genotypes of the parent plants? Include a punnett square in your answer.

Parent Genotypes:_________________

_________________

7

2. Kory also planted snapdragons in his garden. All of his seeds came from one set of parents. When his plants bloomed, 50% were white and 50% were pink. What were the genotypes of the parent plants? Include a punnett square in your answer.

Parent Genotypes:_________________

_________________

8

3. Casie, Zach, and Kelly each have beautiful gardens of snapdragon flowers. Casie has a garden of red snapdragons and would like to create a new section to her garden including only pink snapdragons.

Zach breeds only pink snapdragons and Kelly breeds white snapdragons. From whose garden will Casie have the greatest probability of creating a pink population of snapdragons flowers?

Create two punnett squares to prove your point.

Casie’s Flowers x Zach’s Flowers

Casie’s Flowers x Kelly’s Flowers

From whose garden will Casie choose “mates” for her flowers?

9

We decide to cross a purebred black chicken with a purebred white chicken; however, we do not know the dominant or recessive color. (That is what we are hoping to find out.) F­in this case is feather.Though, as expected we end up with hybrids, they are not the typical hybrids we would expect…

Co­dominance• chickens….

10

In this case, the offspring had both black and white feathers.

Black + White = Speckled (black and white)

• Therefore, we say that there is NO dominant or recessive gene. The alleles are co­dominant. Both traits are exhibited.

11

Codominance: Both Alleles are DOMINANT and are EQUALLY Expressed in the phenotype.

Pracce Problems:The gene for the coat color of shorthorn cale in inherited by co‐dominance. Red Shorthorn cale have RR genes. White shorthorn cale have WW genes. Roan (coat of both red and white hairs) cale have RW genes1. Determine the genes of offspring of one red cow and one roan bull. Show a punne square. What % of offspring should have red coats? white coats? roan coats?

% red coats: ________

% white coats: ______

% roan coats: _______

12

2. Determine the offspring of two roan parents. Show a punnett square. What percentage of offspring should have red coats? white coats? roan coats?

% red coat: ________ % white coat: ______ % roan coat: _______

13

3. In chickens, the allele for black feathers (B) is codominant with the allele for white feathers (W). Heterozygous chickens appear speckled

with black and white feathers. A black chicken mates with a heterozygous speckled chicken. Show a punnett square.

What are the genotypic and phenotypic ratios?

Genotypic Ratio: ________________________

Phenotypic Ratio: _______________________

14

4. A rooster and chicken mate. When the chicks hatch 3 are speckled, 2 are black and 1 is white. What are the parents’ genotypes? Draw a punnett

square to show your work.

• Parent’s Genotypes: ____________ and____________

15

• Practice: Codominance and Incomplete Dominance

16