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.
IB 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:
IAI
A= type A blood
IAi= type A blood
IAI
B= type AB blood
IBI
B= type B blood
IBi= 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?
IAIB IAi
IBi ii
IA
i
IB i
How disorders occur.
Nondisjunction will lead to abnormal numbers of chromosomes in the cells.
Figure 15.11 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.