Mendelian InheritancePart 2

BIO 2215

Oklahoma City Community College

Dennis Anderson

Multiple Alleles

• More than two forms of an allele exist in a population

• An individual only has two of the alleles

A allele for making the A antigen on red blood cells

B allele for making the B antigen on red blood cells

O allele for NOT making the A or B antigen on red blood cells

Multiple Blood Alleles

AA or AO = Type A blood

BB or BO = Type B blood

AB = Type AB blood

OO = Type O blood

Three alleles give four blood types

California Court Case

• 1946 the California supreme court ruled that Charlie Chaplin was the biological father of a child he claimed was not his.

• His defense was that the baby had type B blood. He had type A and the woman who sued him had type O (These may not be the actual blood types, but it illustrates the point)

• Was the court correct?

O

O

A AO

OO

AO

OO

O

AA, AO = Type A

BB, BO = Type B

AB = Type AB

OO = Type O

The judge should take a course in zoology!

Mutation

• Change in a gene– nucleotide sequence is often altered– Produce abnormal protein

• Cause a disease (sickle cell anemia)• Resistance to a disease (AIDS)

Levels of Mutation

• Molecular level– Deletion of nucleotides– Addition of nucleotides– Substitution of nucleotides

• Chromosomal level– Change in structure– Change in number of chromosomes

Mutant

• Unusual phenotype

• Mutations cause mutants

Normal Mutant

Has different phenotype because of a change in his DNA

Hemoglobin

• Protein molecule made of 4 globin chains– 2 alpha chains with 141

amino acids– 2 beta chains with 146

amino acids

Sickle Cell Anemia

• Gene for making hemoglobin is changed from normal

Normal Hemoglobin Beta ChainFirst six amino acids

CTC

Valine Histidine Thre..

Leucine Glutamic acidProline

CAC

Valine Histidine Thre..

Leucine ValineProline

Hemoglobin S Beta ChainFirst six amino acids

One nucleotide has changed

Hemoglobin S

• Forms long rod like molecules that stretch RBC into a sickle shape

• Sickled cells obstruct circulation of blood• Allele for hemoglobin S is recessive• SS = Normal• Ss = Carrier• ss = Sickle cell anemia

Why is the s allele more common in Blacks than Whites?• Ancestors of Blacks lived in areas where

malaria was present

• Malaria parasite cannot survive on hemoglobin S– Even Ss are immune to malaria

• The s allele is beneficial in an environment where malaria is present

Beta Globin Mutations

• Over 300 different mutations!

Causes of Mutations

• Spontaneous– Random– About 1/100,000 chance of a gene mutating

• Induced– Caused by mutagens

• X-rays…break DNA• UV radiation….Thymine dimers• LSD…Break chromosomes• Cigarette smoke…damages tumor suppressor

genes

Spontaneous Mutation

• Two people of normal height have a child with dwarfism

• Bacteria become resistant to antibiotics• Cold virus mutates every year

– Immunity for this years cold will not protect you from next years cold

• AIDS virus mutates too fast to make a conventional vaccine

Ultraviolet LightCauses adjacent Thymines to bond together

ACA TT CT G

ACA TT CT G

Excision Repair EnzymeRemoves small section of DNA

ACA TT CT G

Excision RepairRemoves small section of DNA

CA T C

ACA TT CT G

DNA Polymerase fills in missing nucleotides

Xeroderma Pigmentosum

• Skin blisters from sun exposure

• Develop skin cancer as children

• Recessive gene does not produce DNA repair enzyme

Sunlight Exposure Increases the Risk of Skin Cancer

• DNA repair enzymes do not always fix the damage that sunlight inflicts on DNA of skin cells.

• The more a person is exposed to sunlight, the greater the risk of skin cancer

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

Homologous Pairs Separate

Four Gametes With Single Chromosomes

Fertilization

Nondisjunction

One pair of chromosomes fails to separate during meiosis

Trisomy

Zygote ends up with 3 chromosomes instead of 2 for a given chromosome pair.

Karyotype

• Picture of chromosomes

• Often arranged with autosomes in descending order and sex chromosomes separate

Normal Male

Normal Female

Trisomy 21Down Syndrome

Down Syndrome

• Large tongue• Flat face• Single crease across

palm• Slanted eyes• Mental retardation

– Some are not

Maternal Age & Down Syndrome

Trisomy 18Edward Syndrome

Edward Syndrome

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

Trisomy 13Patau Syndrome

Patau Syndrome

• Cleft lip and palate• Extra fingers & toes

– polydactylism

• Defects– Heart– Brain– Kidney

• 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

Abnormal Chromosome Numbers

• Aneuploidy– Missing or extra

chromosome

• Polyploidy– Extra set of

chromosomes– Usually lethal– Common in cancer– Common in plants

Fetal testing can determine abnormal karyotypes

The End