Medical Genetics

Human Anatomy and Physiology II

Oklahoma City Community College

Dennis Anderson

Mitosis

• Produces daughter cells with 46 chromosomes• Used in growth and repair

Mitosis

• DNA is duplicated• Doubled

chromosomes form from duplicated DNA

• Each cms has 2 identical chromatids

Chromatid

Chromatid

Chromosomes line up in a single row.

Mitosis Metaphase

Chromosomes separate

Each chromatid becomes a single chromosome

Meiosis

• Reduce the chromosome number to half that of body cells

• Produce gametes– Egg– Sperm

Chromosomes line up in a double row.

Meiosis Metaphase

Chromosomes separate

Each each daughter cell gets doubled chromosomes

Doubled Chromosomes Separate in Second Meiotic Division

Mitosis Metaphase

Meiosis Metaphase

Cms 1 Cms 1

Cms 2 Cms 2

Double Filed Chromosomes

• Daughter cells receive ONE of each cms pair

• Daughter cells receive ONE allele for most traits

• New combinations of alleles possible

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

• Represented by a single letter

Dwarfism = D

Normal height = d

DD = Dwarfism

Dd = Dwarfism

dd = Normal height

Examples of Alleles

Dwarf Band

Dominant & Recessive Alleles

• 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

Homozygous

• Both alleles alike

• AA or aa

Heterozygous

• Alleles are different

• Aa

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

Homologous chromosomes line up in a double file in metaphase I of meiosis

Homologous Pairs Separate

Four Gametes With Single Chromosomes

Fertilization

Nondisjunction

Trisomy

Sex Chromosomes

Sex Chromosomes

• Male have Xy– Male gametes have either X or y

• Females have XX– Female gametes have X

AutosomesChromosomes 1-22

X-Linked Traits

• Alleles are on the X chromosome

• Females have two alleles

• Males have one allele– Only one X chromosome

Normal Male

Normal Female

Trisomy 21Down Syndrome

Down Syndrome

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

palm• Mental retardation

– Some are not

Maternal Age & Down Syndrome

Trisomy 18Edward Syndrome

Edward Syndrome

• Heart defects• Displaced liver• Low-set ears• Abnormal hands• Severe retardation• 98% abort• Lifespan < 1 year

Trisomy 13Patau Syndrome

Patau Syndrome• Cleft lip and palate• Extra fingers & toes

– polydactylism

• Defects– Heart– Brain– Kidneys

• Most abort• Live span < 1 month

Klinefelter Syndrome

Klinefelter Syndrome

• Breast development• Small testes• Sterile• Low intelligence

– Not retarded

Klinefelter Website

Turner Syndrome

Turner Syndrome

• Short• Not go through

pruberty• Produce little estrogen• Sterile• Extra skin on neck

Fetal Testing

Sickle Cell Anemia

• RBCs sickle shaped

• Anemia

• Pain

• Stroke

• Leg ulcers

• Jaundice

• Gall stones

• Spleen, kidneys & lungs

Sickle Cell Anemia

• Recessive allele, s codes for hemoglobin S – Long rod-like molecules– Stretches RBC into sickle shape

• Homozygous recessive, ss have sickle cell anemia

• Heterozygous, Ss are carriers

Hemophilia

Blood clotting impaired

Recessive allele, h

carried on X cms

X-linked recessive trait

More common in males

Albinism

• Lack of pigment– Skin

– Hair

– Eyes

Amino Acids Melanin PigmentEnzyme

A a

AA = Normal pigmentation

Aa = Normal pigmentation

aa = Albino

PKU Disease

• Phenylalanine excess• Mental retardation if

untreated

Molly’s Story

Phenylalanine TyrosineEnzyme

P p

PP = Normal

Pp = Normal

pp = PKU

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

X-linked Recessive Traits

• Alleles are on the X chromosome

• Inheritance pattern different in males and females

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

The End