Patterns of Inheritance

Incomplete Dominance, Codominance, Multiple Alleles, Genetic Disorders, &

Sex-Linked Genes

I) Incomplete Dominance

A) Snapdragon Flowers

I) Incomplete Dominance

B)Individual has a trait that appears to be an intermediate form of the traits displayed by each parent

• R = Red• W = White• RW=Pink

• R = W

• Pink X Pink Flower Cross

I) Incomplete Dominance

R

WW

RR

R

W

W

RW

RW

• Genotypes–RR: 1

–RW: 2

–WW: 1

• Phenotypes–Red: 1

–Pink: 2

–White: 1

II) Codominance

A) Roan Horse Color

II) Codominance

B)Both genes of the heterozygote are fully expressed; thus, you see both colors

II) Codominance

• R = Red

• W = White

• RW = Roan (Red/White)

• R = W

• Roan X Roan Horse Cross

R

WW

RR

R

W

W

RW

RW

• Genotypes–RR: 1

–RW: 2

–WW: 1

• Phenotypes–Red: 1

–Roan: 2

–White: 1

III) Multiple Alleles

A) Human ABO Blood Types

III) Multiple AllelesB)Some traits are

controlled by genes that have more than two alleles

III) Multiple Alleles• iA > i• iB > i• iA = iB

• iAiA or iAi = A-Blood• iBiB or iBi = B-Blood• ii = O-Blood• iAiB = AB-Blood• Cross a heterozygous A-

blood man with a heterozygous B-blood woman

iB

ii

iAiB

iA

i

i

iAi

iBi

• Genotypes–iAiB: 1

–iBi: 1

–iAi: 1

–ii: 1

• Phenotypes–AB Blood: 1

–B Blood: 1

–A Blood: 1

–O Blood: 1

IV) Sex-Linked Inheritance

A) Colorblindness & Hemophilia

IV) Sex-Linked InheritanceB) Colorblindness: genetic disease characterized

by the inability to see certain colors (there are different types of colorblindness)

1) Mutation is on the X-chromosome

C) Hemophilia: genetic disease characterized by the blood’s inability to clot

1) Mutation is on the X-chromosome

IV) Sex-Linked Inheritance

• X > XC

• Y plays no part

• XX = Normal ♀• XXC = Carrier ♀• XCXC = Colorblind ♀• XY = Normal ♂• XCY = Colorblind ♂• Cross a carrier ♀ with

a normal ♂

X

XCY

XX

X

Y

XC

XY

XXC

• Genotypes–XX: 1

–XXC: 1

–XY: 1

–XCY: 1

• Phenotypes–Normal ♀: 1

–Carrier ♀: 1

–Normal ♂: 1

–Colorblind ♂: 1

V) Polygenic Traits

A) Interaction of several genes

VII) Polygenic Traits

B) Traits controlled by two or more genes

C) Often show a wide range of phenotypes

V) Polygenic Traits

VI) Pedigrees

VI) Genetic Disorders

A) Sickle-Cell Anemia & Cystic Fibrosis

VI) Genetic DisordersA) Sickle-Cell Anemia:

1) Recessive disorder affecting hemoglobin, on chromosome #11

2) Gives red blood cells a deformed appearance

3) Heterozygous carriers are more immune to malaria; Recessives are immune to malaria

4) Malaria afflicts 300-500 million a year, killing nearly 3 million a year (largest killer in the world)

VI) Genetic DisordersB) Cystic Fibrosis:

1) Recessive disorder on chromosome #72) Mucous builds-up, making it difficult to

breath & digest food; this allows bacteria to damage the linings of the lungs (often fatal by early adulthood)

3) Heterozygous carriers are more immune to not dehydrating from cholera, & recessives are immune to cholera

4) Cholera afflicts hundreds of thousand yearly, killing many thousands