Patterns of

Inheritance Part 2

Exceptions to Mendel’s Law

• Mendel’s traits showed two distinct forms

• Most genes do not exhibit simple inheritance

• Genotypic and phenotypic ratios may vary

because of interactions between

– Alleles

– Other genes

– Segregation of genes on the same chromosome

– Environment

Complex Inheritance and Human Heredity

Incomplete Dominance

Pattern of inheritance in which one allele is not

completely dominant over another

RR=red

R1R1=white

RR1 =pink

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Complex Inheritance and Human Heredity

Codominance

Inheritance

pattern in which

both alleles show

at the same time

equally

BB=black

B1B1=white

BB1 =roan

Chapter 11

Roan horse is mix of

black and white hairs

Mix of red and

white petals

Complex Inheritance and Human Heredity

Multiple Alleles C=full color

ch=himalayan

c=albino

cch=chinchilla

Chapter 11

Some genes may

have more than

just two

alternative forms

of a gene

In rabbits, four

alleles code for

coat color:

Complex Inheritance and Human Heredity

Multiple Alleles

More than 2 alleles

determine genotype

Blood groups in

humans have 3 alleles

─IA

─IB

─i

11.2 Complex Patterns of Inheritance

Chapter 11

Complex Inheritance and Human Heredity

Multiple Alleles

Having 3 alleles

produces a total of 6

possible genotypes

and 4 possible

phenotypes.

Phenotype IS THE

SAME AS THE blood

type.

(A, B, AB, O)

11.2 Complex Patterns of Inheritance

Chapter 11

Complex Inheritance and Human Heredity

Epistasis

One allele hides the effects of another allele.

In Labs, black coat color is dominant over yellow

and how dark – very dark (B) or light (b).

E=dark pigment or not B=how dark pigment is

E=dark fur e=light fur B=very dark b=not dark

No dark pigment present in fur Dark pigment present in fureebb

eeB_E_bb E_B_

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Complex Inheritance and Human Heredity

Sex-Linked Traits

Genes located on the X chromosome –

XC = colorblind

Xh = hemophilia

Includes:

Red-green color blindness

Hemophilia: blood does not

clot

11.2 Complex Patterns of Inheritance

Chapter 11

Complex Inheritance and Human Heredity

Polygenic Traits

Polygenic traits arise from the interaction of

multiple pairs of genes. Includes height and

skin color in humans.

Chapter 11

Dihybrid CrossDihybrid cross

– Involves the

cross of TWO

traits

– Uses a 16 block

Punnett square

• “F.O.I.L.” to

produce

gametes

Complex Inheritance and Human Heredity

Environmental Influences

Environmental factors

Diet and exercise

Sunlight and water

Temperature

Chapter 11