Genetics Lecture 2 - Mendelian Inheritance Flashcards
(21 cards)
Name the three principles of heredity.
- Unit inheritance.
- Segregation.
- Independent assortment.
What is meant by “unit inheritance?”
Parental phenotypes do not blend.
What is segregation?
One member of each gene pair is transmitted to offspring.
What is independent assortment?
Genes at different locations in the chromosome are transmitted independently.
What is achondroplasia?
Autosomal dominant disorder - “little people.” Most common skeletal dysplasia.
What is assortative mating?
ex. little people get with other little people.
What is variable expressivity?
When features of a disorder vary amongst individuals, even those within the same family. Ex. Marfan syndrome. Think dimmer switch.
What is Marfan syndrome?
Autosomal dominant (don’t need to memorize that), systemic disorder of connective tissue. Major source of mortality is dilation and rupture of the aorta.
What is incomplete penetrance?
Not all individuals with a mutation have phenotypic effects. Ex. BRCA gene mutations. Think on/off switch.
What is a BRCA mutation?
The BRCA genes are tumor suppressor genes. Mutations of these genes predispose people to hereditary breast-ovarian cancer syndrome.
What is a de novo mutation?
A new mutation. They usually occur at “hot spots.” Ex. achondroplasia - 80% of cases are due to de novo mutations. De novo mutations occur at higher rates when people age.
What inheritance pattern does CF follow?
Autosomal recessive. Note: 1 in 25 caucasians are carriers.
What inheritance pattern does sickle-cell anemia follow?
Autosomal recessive. Most common inherited blood disorder in the U.S. 1 in 8 African Americans are carriers.
What is lyonization?
Random X chromosome inactivation in females. Note that skewed x-linked inactivation may lead to symptomatic female carriers.
Name the rare scenarios in which a female may be affected by a X-linked recessive disorder.
- She has a 45,X karyotype
- She has an X chromosome rearrangement which results in skewed X-inactivation
- She has an affected father and carrier mother (rare)
- Disorder is genetically heterogeneous (the condition may have non-X-linked recessive cause)
What inheritance mode does Incontinenta Pigmenti follow?
X-linked dominant.
How is mitochondrial disease inherited?
It is maternally inherited from the mother. Ex. MELAS: mitochondrial encephalomyopathy, lactic acidosis, and stroke-like episodes.
With regards to mitochondrial disease, define heteroplasmy.
Mix of normal and abnormal DNA.
With regards to mitochondrial disease, define homoplasmy.
All mtDNA is the same (normal or mutated).
Define threshold effect.
Only at a certain % of abnormal mitochondrial DNA is when a patient will become symptomatic for a disorder.
Define haplotype.
A group of SNPs that are always observed together.
