Human Genetics Blood, Disorders and Pedigrees

Multiple Alleles Several alleles can be present for the gene locus. Only two are carried at a time! Human blood type is a good example A, B, AB, and O. (Phenotypes) Blood shows complete dominance and codominance. A and B are codominant and O is recessive to both.

Alleles in blood These alleles are written a little differently than the other alleles we have seen: I A is the allele for A type blood. I B is the allele for B type blood. i is the allele for the O type blood. –FYI…… 44% are O, 35% are A, 16% are B and 5% are AB in the world.

Genotypes and Phenotypes of Multiple Alleles The 6 possible genotypes give 4 phenotypes: I A I A = type A blood I A i = type A blood I A I B = type AB blood I B I B = type B blood I B i = type B blood ii = type O blood

Multiple alleles A heterozygous type “A” man is married to a heterozygous type “B” woman. Can they have a type O baby? A type AB baby? IAIBIAIB IAiIAi IBiIBiii IAIA i IBIB i

How disorders occur. Nondisjunction will lead to abnormal numbers of chromosomes in the cells.

Figure Meiotic nondisjunction

Chromosomal disorder terms Autosomal- chromosomes 1-22 Sex Chromosomes- the “X” and “Y” chromosomes Aneuploidy - means having too few or too many of one chromosome. Trisomy- means having 3 copies of one particular chromosome, rest of karyotype normal diploid (2n +1) Monosomy- means having 1 copy of one particular chromosome, rest of karyotype normal diploid (2n -1)

Down Syndrome Trisomy 21 (2n +1)

Characteristic physical features A flattened face Heart problems Mild to moderate hearing loss Visual problems Average life expectancy of about 50 years. Some degree of learning disability The chance of a woman having a baby with Down's syndrome increases as she gets older. Only 1 in 2000 births from teenage mothers are affected by Down's syndrome, but this goes up to 1 in 10 in 48-year-old women. However, 80% of babies with Down's syndrome are born to women under 35, since these women account for the majority of the childbearing population.

Sex Chromosome Disorders Turner syndrome - Monosomy X - only one X chromosome, no Y - phenotype female, sterile, slight physiological abnormalities (2n -1) Klinefelter syndrome - Disomy X, XXY, phenotype male, sterile, developmental problems (2n +1)

Turner and Klinefelter

Autosomal Chromosome Disorders Dominant –Huntington Disease is a found on chromosome 4. –Makes too much Huntingtin protein and damages the brain. Recessive –Phenylketonuria (PKU) is found on chromosome 12. –Does not break down phenylalanine (aa) and builds up and damages the brain.

Dominant vs. Recessive

Pedigrees Pedigrees are used to track a trait through several generations of a family. Geneticists use them to find the location of abnormal genes

Pedigree symbols

Which one is correct?

Generations in a pedigree Generation I is the grandparents Generation II is your mom and dad and your aunts and uncles. Generation III is you, your brothers and sisters and your first cousins.

A Whirling Pedigree You can determine the genotype of an individual by looking at the family pedigree. What is the genotype of individual #8 if whirling (W) is a dominant trait?

Example of a pedigree for the royal family of Europe.