Gene• A unit of heredity

that controls the development of one trait

• Made of DNA

Allele• Member of a paired gene

– One allele comes from each parent• Dominant alleles are expressed• Recessive alleles are not expressed in the presence of a

dominant allele– Recessive alleles are only expressed if both recessive alleles

are present

Dwarfism = D

Normal height = d

DD = Dwarfism

Dd = Dwarfism

dd = Normal height

Examples of Alleles

Dwarf Band

Genotype• Genetic make up• Represented by alleles• DD & Dd are genotypes for dwarfism

Phenotype

• A trait• Genotype determines the phenotype• Dwarfism is a phenotype

Codominant

• Two different alleles are both dominant

• A = allele for type A blood• B = allele for type B blood• AB = results in type AB blood

Karyotype

• Picture of chromosomes from an individual

Homologous Chromosomes

• Chromosomes of the same pair• Karyotypes are usually arranged with

homologous chromosomes paired together

Mutation• Change in a

gene or chromosome

• Causes an abnormal trait

MutagenAgent that causes mutations

•Cigarette smoke

•Pesticides

•X-rays

•Ulatraviolet light

•Nuclear radiation

Sex Chromosomes• Male have Xy

– Male gametes have either X or y

• Females have XX– Female gametes have X

AutosomesChromosomes 1-22

X-Linked (vs Y- linked)Traits

• Why are there more X-linked that Y- linked disorders?

• Who suffers more frequently from sex-linked disorders? Why?

Which karyotype is which?A B

Trisomy 21: Down Syndrome

• Large tongue• Flat face• Slanted eyes• Single crease

across palm• Mental

retardation– Some are not

Maternal Age & Down Syndrome

Trisomy 18: Edward Syndrome

• Heart defects• Displaced liver• Low-set ears• Abnormal hands• Severe

retardation• 98% abort• Lifespan < 1 year

Trisomy 13: Patau Syndrome

• Cleft lip and palate• Extra fingers & toes

– polydactylism

• Defects– Heart– Brain– Kidneys

• Most abort• Live span < 1

month

Klinefelter Syndrome• Breast

development• Small testes• Sterile• Low intelligence

– Not retarded

Klinefelter Website

Turner Syndrome

• Short• Not go

through puberty

• Produce little estrogen

• Sterile• Extra skin on

neck

Fetal Testing

Complete Dominance

Incomplete Dominance

CO-Dominance

Multiple Alleles

Sex-Linked Traits

Number of Alleles

2 2 2 3

Example of Alleles

Aa

AA’

AB

IA IB i XA Xa

Heterozygote Phenotype

Dominant parent Neither parent Both parents Dominant OR both parents

depends

Number of genotypes

3 3 3 6 5

Possible Genotypes

AA, Aa, aa AA, AA’, A’A’ AA, BB, AB IA IA, IB IA, IA I, IB IB, IBi, ii,

XA XA, XA Xa, XaXa, XAY, XaY,

Number of phenotypes

2 3 3 4 2

Possible phenotypes

A, B A, A’ , AA’ A, B, AB A, B, AB, O A, a

Classical Example

Pea plants 4 o clock flowers

Roan cows ABO Blood group

HemophiliaColor blindness

Example Blue eyes X purple eyes = blue eyes

Blue eyes X purple eyes = green eyes

Blue eyes X purple eyes = blue and purple eyes

various Males determines daughters and mother determines son

A man & woman are both carriers (heterozygous) for albinism. What is the chance their children will inherit albinism?

AA = Normal pigmentation

Aa = Normal pigmentation (carrier)

aa = Abino

Man = Aa Woman = Aa

A

a a

A

A

a

a

A AA

Aa

Aa

aa

AA

Aa

Aa

aa

Genotypes1 AA, 2Aa, 1aa

Phenotypes

3 Normal

1 Albino

Probability

25% for albinism

A man & woman are both carriers (heterozygous) for PKU disease. What is the chance their children will inherit PKU disease?

p

p

P PP

Pp

Pp

pp

P

PP = Normal

Pp = Normal (carrier)

pp = PKU disease

PP

Pp

Pp

pp

Genotypes1 PP, 2Pp, 1pp

Phenotypes

3 Normal

1 PKU disease

Probability

25% for PKU disease

A man with sickle cell anemia marries a woman who is a carrier. What is the chance their children will inherit sickle cell anemia?

s

s

s Ss

Ss

ss

ss

S

SS = Normal

Ss = Normal (carrier)

ss = Sickle Cell

Ss

Ss

ss

ss

Genotypes2 Ss, 2ss

Phenotypes

2 Normal (carriers)

2 Sickle cell

Probability

50% for Sickle cell

A man with heterozygous dwarfism marries a woman who has normal height. What is the chance their children will inherit dwarfism? Dwarfism is dominant.

d

d

D Dd

dd

Dd

dd

d

DD = Dwarf

Dd = Dwarf

dd = Normal

Dd

dd

Dd

dd

Genotypes2 Dd, 2dd

Phenotypes

2 Normal

2 Dwarfs

Probability

50% for Dwarfism

XH XH = Normal Female

XH Xh = Normal Female (Carrier)

Xh Xh = Hemophilic Female

XHy = Normal Male

Xhy = Hemophiliac Male

A man with hemophilia marries a normal woman who is not a carrier. What is the chance their children will inherit hemophilia? Hemophilia is X-linked recessive.

y

XH

Xh XH Xh

XH

Xh XH = Normal Female

XH Xh = Normal Female (Carrier)

Xh Xh = Hemophilic Female

XHy = Normal Male

Xhy = Hemophiliac Male

XH Xh

XHy XHy

Genotypes

2 XH Xh, 2XHy

Phenotypes

2 Carrier Females

2 Normal Males

Probability

O% for Hemophilia

y

XH

Xh XH Xh

XH

XH Xh

XHy XHy

A normal man marries a normal woman who is a carrier for hemophilia. What is the chance their children will inherit hemophilia?

y

Xh

XH

XH

Xh XH = Normal Female

XH Xh = Normal Female (Carrier)

Xh Xh = Hemophilic Female

XHy = Normal Male

Xhy = Hemophiliac Male

XH XH XH Xh

XHy Xhy

Genotypes

XH XH , XH Xh, XHy, XhyPhenotypes

2 Normal Females

1 Normal Males

1 Male Hemophiliac

Probability50% for Male Hemophilic

0% for Female Hemophilic

y

Xh

XH XH XH

XH

XH Xh

XHy Xhy