NOTES PG. #16: COMPLEX GENETICS

EQ: ARE THERE OTHER, MORE COMPLICATED, TYPES OF INHERITANCE?

INCOMPLETE DOMINANCE

• Incomplete Dominance - Situation in which one allele is not completely dominant over another- phenotypes mix/blend.• Example When straight hair and curly hair are crossed, wavy

hair results.• Alleles:

• S= Straight (dominant)• S’= Curly (recessive)

• Genotype=Phenotype:• SS =Straight hair• SS’=Wavy hair• S’S’=Curly hair

INCOMPLETE DOMINANCE IN RATS

• If you crossed a white rat and a black rat using incomplete dominance what offspring would you get?

+

Discuss with your

neighbor!

EXAMPLE INCOMPLETE DOMINANCE PUNNETT:

Red and white flowers are crossed and pink flowers are produced.

Genotype=Phenotype:RR=RedRR’=PinkR’R’=White

YOU TRY: INCOMPLETE DOMINANCE

• #1: Cross a curly-haired mother with a wavy-haired father, then summarize the genotype & phenotype percentages: Genotype=Phenotype:

SS =Straight hairSS’=Wavy hairS’S’=Curly hair

CODOMINANCE• Codominance - Situation in which both alleles of a

gene contribute equally to the phenotype of the organism.

• Example – A solid white cow is crossed with a solid black cow and the resulting offspring are spotted black and white (spotted is also called roan).• Alleles: W=white, B=Black• Genotype = Phenotype:• WW=White cow, BB= Black cow, WB=White & Black spotted cow

[NOT gray!]

• +

EXAMPLE CODOMINANCE PUNNETT:• If you cross a red and white flower, you get a

flower with red & white splotches.Genotype = Phenotype:• RR=Red• WW=White• RW=Red &

White spots[NOT a mix- NOT pink!]

CO-DOMINANCE IN RATS

• If you crossed a white rat and a black rat using codominance what offspring would you get?

+

Discuss with your

neighbor!

YOU TRY: CODOMINANCE• #2: Cross a speckled “erminette” chicken with a

white chicken. Summarize the genotype and phenotype results as percentages:

LABEL THE PICTURESWhen you cross a red & white flower, what do you get?

1. If red is dominant /with regular [complete] dominance?2. With incomplete dominance?3. With codominance?

CHECK YOURSELF: WHICH TYPE OF INHERITANCE IS THIS?

Incomplete dominance!

CHECK YOURSELF: WHICH TYPE OF INHERITANCE IS THIS?

Incomplete dominance!

CHECK YOURSELF: WHICH TYPE OF INHERITANCE IS THIS?

Co-dominance!

CHECK YOURSELF: WHICH TYPE OF INHERITANCE IS THIS?

Tall plant

Short plant

Medium plant

Incomplete dominance!

CHECK YOURSELF: WHICH TYPE OF INHERITANCE IS THIS?

Codominance!

CHECK YOURSELF: WHICH TYPE OF INHERITANCE IS THIS?

Codominance!

CHECK YOURSELF: WHICH TYPE OF INHERITANCE IS THIS?

Incomplete Dominance!

MULTIPLE ALLELES

• Multiple Alleles- Three or more alleles of the same gene.• Even though three or more alleles exist

for a particular trait, an individual can only have two alleles - one from the mother and one from the father.

EXAMPLES OF MULTIPLE ALLELES

1. Coat color in rabbits is determined by a single gene that has at least four different alleles. Different combinations of alleles result in the fur colors you see here.

EXAMPLES OF MULTIPLE ALLELES2. Blood Type – 3 alleles

exist (IA, IB, and i), which results in four different possible blood types

3. Hair Color – Too many alleles exist to count• There are over 20

different shades of hair color.

MULTIPLE ALLELES: HUMAN BLOOD TYPES

The 4 human blood types A, B, AB & O made from 3 alleles: lA, lB, & i• lA & lB are dominant to i • lA & lB are codominant

HUMAN BLOOD TYPES

4 Human Blood Types:

lA lA or lAilB lB or lBilA lBii

Genotypes Surface Molecules PhenotypesAB

A and BNone

ABABO

EXAMPLE: BLOOD TYPES

• What are the genotype & phenotype chances for this offspring?

YOU TRY: BLOOD TYPE PUNNETT

• Cross a Mother who is heterozygous for blood type B, with a Father who has blood type AB:

• What are the genotype and phenotype percentages?

MULTIPLE ALLELES• There Are Always Multiple Alleles!

• Genetic inheritance is often presented with straightforward examples involving only two alleles with clear-cut dominance. This makes inheritance patterns easy to see.

• But very few traits actually only have two alleles with clear-cut dominance. As we learn more about genetics, we have found that there are often hundreds of alleles for any particular gene. • We probably know this already - as we look around at

other people, we see infinite variation.

POLYGENIC TRAIT

• Polygenic Trait - Trait controlled by two or more genes.• Polygenic traits often show a

wide range of phenotypes. • Example: The wide range of

skin color in humans comes about partly because more than four different genes probably control this one trait... No wonder DNA is soooo looooong!