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.