Human Genetics. Understanding Genetics with Family Trees. How do we use Mendel’s Observations about Dominant and Recessive Traits, Segregation and Independent Assortment to predict the inheritance of traits in humans?. Pedigree the family tree
Download Policy: Content on the Website is provided to you AS IS for your information and personal use and may not be sold / licensed / shared on other websites without getting consent from its author.While downloading, if for some reason you are not able to download a presentation, the publisher may have deleted the file from their server.
Understanding Genetics with Family Trees
How do we use Mendel’s Observations about Dominant and Recessive Traits, Segregation and Independent Assortment to predict the inheritance of traits in humans?
Individuals I1 and III1 express the unusual trait being studied
Rest have normal phenotypes
Proband - the first afflicted member of a family seeking medical attention.
- marked with the an arrow and the letter p
The family tree
Distal symphalangism is an autosomal dominant disorders characterized by fusion of the proximal or distal interphalangeal joints.
Comparison of autosomal dominant and autosomal recessive inheritance
Males and females affected?
Males and females transmit the trait?
Trait skips generations?
At least one parent of affected child must be affected?
Gene for blood group in humans has 3 alleles
IA IB and IO
There are only two alleles for each gene present in a normal diploid individual
3 alleles -- IA , IB , and IO
IA and IB are codominant
IO is recessive
Type A blood can be IAIA or IAIO
Type B blood can be IBIB or IBIO
Type AB blood is IAIB - codominant state
Type O blood is IOIO
Heterozygous phenotype is intermediate between the two parental homozygotes.
The heterozygous phenotype is typically intermediate to the homozygous phenotype.
If you cross true breeding red and white snapdragons
F1 are all pink flowers
F2 - 1:2:1 red:pink:white
It takes 2 doses of the red allele to get red
RR- red Rr – pink rr - white
Autosomal dominant inheritance
Autosomal dominant inheritance
Who could be carriers?
- at least 2 carriers in generation I
- but all could be carriers
- Autosomal recessive
- Heterozygotes carry the recessive allele but exhibit the normal skin color (sometimes called wild type phenotype)
Offspring 2 marries someone homozygous for the trait. What will their children be if the trait is recessive? Dominant- Heterozygote? Homozygote?
Ellen is not affected and
cannot carry aa genotype
?Statistical Genetic Predictions
Ellen and Michael’s parents must be carriers.
Ellen’s brother Michael has
sickle cell anemia, an autosomal recessive disease.
What is the chance that Ellen’s child has a sickle cell anemia allele (a)?
chance Ellen is a carrier = 2/3
chance child inherits sickle cell allele = 1/2
Overall chance child carries sickle cell allele from Ellen = 2/3 x 1/2 = 1/3
most common – first cousins marriages
- share grandparents - risk passing on the same recessive alleles to offspring
Preferred marriage was brother/sister
Why is so much inbreeding not fatal?
It could have an effect, but the early miscarriages and diminished fertility and infant deaths weren’t recorded.
West Virginia University