Genetics Incomplete and Co-dominant inheritance patterns

Work with a partner and answer the following: · Do you think twins could be

born of two different color

skins? If yes, how do you think

this can happen and if no, why

could this not happen?

Intermediate Patterns of Inheritance

Review: Complete DominanceMendel experiments showed the following:● One homozygous recessive (rr

and white color) X homozygous dominant (RR and purple color) = All off offspring Heterozygous (Rr and Purple color)

● Then, cross two of the F1 offspring (Heterozygous) (Rr and Purple color). All F2 offspring show 3:1 phenotypic ratio or 1:2:1 genotypic ratio

● Well, this is not always the case….

Incomplete dominance● A form of inheritance in

which the heterozygous alleles are both expressed, resulting in a combined phenotype.

● Think: Blending ● Example: Flowers

Recap

● We have examined complete dominance, in which one allele is clearly dominant over the other

● incomplete dominance, in which neither allele dominates over the other.

● In a third type of dominance, codominance, both alleles are expressed in the phenotype of individuals that have heterozygous alleles.

Codominance

In a certain fish, blue scales and red scales are codominant. When a fish has the genotype B R, it has a patchwork of blue and red scales. What happens if you breed this fish with a fish that only has Blue Scales.

Step 1: Determine the genotypes of the parentsB R = patchwork fishB B = blue fishR R = red fish

Step 2: Set up the box!

1/2 will by patchwork, 1/2 will be blue

Step 3: Count the number of each phenotype:

What happens when you cross two patchwork fish? Solve?

1: BB2: BR1: RR

Multiple Alleles- Three or more alleles for a

particular gene

● Great Example: Human Blood Type● 3 Alleles for the 1 gene that determines your blood

type (Remember you only have 2 of the 3 alleles- one from each parent)

● Four possible phenotypes

One more example- Work with a partner and

solve the following problem:

Genotype: PhenotypeBlood type A: IA IA

Blood type B: IBIB

Blood type AB: IAIB

What is the probability of having a child with a different genotype, if mother has type A blood type and father has type B blood type? Be sure to include genotypes and phenotypes in your work:

● Complete an F1 generation cross, show your work and then complete an F2 cross. Show your work

Answer: genotype and phenotype ratio both 1:2:1

● red blood cells have special markers called antigens

● Type AB has both antigens,

Color Blindness- How is this inherited?

● Work with a partner and think of possible two reasons of how a person could inherit color blindness?

● List two challenges an individual could face if color blind.

Sex-linked Traits “Gender”50% chance of being male or 50% chance of being female

● Gender determined from Dad, because mom will always supply an X

What does it mean to have a sex-linked trait?

If the gene is recessive, then males only need one such recessive gene to have a sex-linked trait rather than the customary two recessive genes for traits that are not sex-linked. This is why males exhibit some traits more frequently than females.

So...Henry the VIIIDecapitated Anne Boleyn because no male heirs….

Sex-Linked Example: Hemophilia

• genetic disorder, impair the body's ability to control blood clotting

• recessive, What does that mean? .

Polygenic Traits

● Trait controlled by more than one gene

o The result is the perception of continuous gradation in the

expression of these traits.

o specialized skin cells produce the pigment, melanin

● Height, skin color and even eye color (recently discovered)

● Example: Skin color

o A genotype of AABBCC would express dark skin

o A genotype of aabbcc would express light skin

Test Cross

● Test crosses involve breeding the individual in question with another individual that expresses a recessive version of the same trait.

● Test cross = the cross of an organism with an unknown dominant genotype with an organism that is homozygous recessive for that trait

● If all offspring display the dominant phenotype, the individual in question is homozygous dominant

● if the offspring display both dominant and recessive phenotypes, than the individual is heterozygous.

Test Cross

Guinea Pig Test Cross

I hand you a black Guinea pig (BB or Bb) and ask you, what is the genotype?

Preform a test cross to identify genotype of the black Guinea pig.

To perform an actual test cross with this guinea pig, we would need a guinea pig (of the opposite sex) that is homozygous recessive ("bb").

In other words, we would need a white guinea pig to mate with our black guinea pig.

Work both crosses to determine genotype!