Mendelian Inheritance Part 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

Multiple Blood 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

Three alleles give four blood types AA or AO = Type A blood BB or BO = Type B blood AB = Type AB blood OO = Type O blood

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 A AO OO AA, AO = Type A BB, BO = Type B AB = Type AB OO = Type O O 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 Chromosomal 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 Chain First six amino acids Valine Histidine Thre.. Leucine Glutamic acid Proline CTC Hemoglobin S Beta Chain First six amino acids CAC Valine Histidine Thre.. Leucine Proline 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 Induced 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 Light Causes adjacent Thymines to bond together

Excision Repair Enzyme Removes small section of DNA G

Excision Repair Removes small section of DNA 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 21 Down Syndrome

Down Syndrome Large tongue Flat face Single crease across palm Slanted eyes Mental retardation Some are not

Maternal Age & Down Syndrome

Trisomy 18 Edward Syndrome

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

Trisomy 13 Patau Syndrome

Patau Syndrome Cleft lip and palate Extra fingers & toes Defects 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