Non-Mendelian Genetics

• Thus far, all of the genes which we have studied have had only 2 possible forms or ALLELES.

• (Brown or white, tall or short, freckled or not.)

• One of each of the allele pair was the DOMINANT allele and one the RECESSIVE.

• Things are about to become more complicated, because some traits are inherited in a different manner.

Non-Mendelian

• Patterns of inheritance that do NOT follow Mendel’s laws. – Incomplete dominance– Co-dominance– Multiple Alleles– Sex-linked inheritance– Polygenic traits

Continuous Variation (Polygenic Traits)

• Multiple genes are involved • Produces many forms of the trait• Examples

– Eye color– Skin color– Hair color– Height

Multiple Alleles and Codominance

Multiple Alleles: • Genes that exist in more than TWO

distinct forms, or have more than 2 alleles.

Codominance: • Cases of multiple alleles in which MORE

THAN ONE of the alleles than is dominant.• If 2 different dominant alleles are present,

THEY WILL BOTH BE EXPRESSED. • They will not blend as in incomplete

dominance.

Other Types of Heredity Patterns

• Codominance – can see both alleles at the same time.– Roan coats in horses

• Some white hairs, some red hairs

Multiple Alleles

• Blood Types in Humans– Single gene, but four phenotypes

• Type A can be AA or Ao• Type B can be BB or Bo• Type AB only AB (codominant pattern here)• Type O only oo (both recessive)

– All 3 blood types are dominant to O

Human Blood TypesThe inheritance of HUMAN BLOOD TYPES

involves both multiple alleles and codominance. Human blood types: • There are FOUR human blood types. • There are THREE alleles for human blood type:

A, B, and O• Two of the alleles are CODOMINANT, one is

recessive. • The alleles are written in the following form: IA,

IB, i (i=O)• The I’s are used to show which alleles are

dominant. • You MUST use both the I’s and the A’s and B’s

when writing genotypes for blood types.

Genotypes for Human Blood Types

• Type A blood: – IAIA or IAi

• Type B blood:– IBIB or IBi

• Type AB blood:– IAIB

• Type O blood: – ii

Human Blood Types

Type You Can Give Blood To You Can Receive Blood From

A+ A+  AB+ A+  A-  O+  O-

O+ O+  A+  B+  AB+ O+  O-

B+ B+  AB+ B+  B-  O+  O-

AB+ AB+ Everyone

A A+  A-  AB+  AB- A-  O-

O- Everyone O-

B- B+ B- AB+ AB- B- O-

AB- AB+ AB- AB- A- B- O-

How to make a blood type Punnett Square

• Punnett Square represents a cross (mating) between a male (on the left side) with blood type IA IB, and a female, (top of square), with blood type A, genotype IAi.1.)What are the possible blood types for the offspring? 2.)What are the ratios or percentages for each possible blood type from this cross? 3.)What blood type is not possible from this cross

Cross IA IB and IAi

male female

Problem completed

IA IA IA i

IA IB IB i

Cross IA IB and IAi

male

Femalemale

IA i

IA

IB

1.)What are the possible blood types for the offspring? 2.)What are the ratios or percentages for each possible blood type from this cross? 3.)What blood type is not possible from this cross 1. A: AB: B

2. 50% A: 25% AB: B 25%

3. O

Another practice problems

• 1. If a woman with type AB blood has a child with a man who has type O blood, then what are the possible blood types of the offspring? (Show your work with a Punnett square.)

Cross= IAIB * ii

Problem completed

Cross= IAIB * ii

• What are the

possible blood types of the offspring?

IA i IA i

IB i IB i

i i

IB

IA

Answer = A and B