mendelian inheritance part 2 bio 2215 oklahoma city community college dennis anderson
TRANSCRIPT
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
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
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
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
Karyotype
• Picture of chromosomes
• Often arranged with autosomes in descending order and sex chromosomes separate
Down Syndrome
• Large tongue• Flat face• Single crease across
palm• Slanted eyes• Mental retardation
– Some are not
Edward Syndrome
• Heart defects• Displaced liver• Abnormal hands• Low-set ears• Severe retardation• 98% abort• Lifespan < 1 year
Patau Syndrome
• Cleft lip and palate• Extra fingers & toes
– polydactylism
• Defects– Heart– Brain– Kidney
• 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
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