Lecture 3: Jan. 25 Transmission genetics: independent assortment Human pedigrees.
Human Genetics Blood, Disorders and Pedigrees Multiple Alleles Several alleles can be present for...
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Transcript of Human Genetics Blood, Disorders and Pedigrees Multiple Alleles Several alleles can be present for...
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.