Week 2: Genetics Flashcards
Define clinical genetics
the study of the transmission of single genes within families and the analysis of more complex types of inheritance
What do clinical geneticists do?
-Diagnosis, genetic counselling, and care of patients with genetic disorders
-Prenatal diagnosis
-Cancer genetics
-Newborn Screening
-Metabolic genetics
-Population screening and preventative medicine
What are the fields within medical genetics?
- Cytogenetics
- Molecular genetics
- Biochemical genetics
Define congenital
present at birth
Define genetic
a heritable disorder
Define consanguinity
the fact of being descended from the same ancestor
Describe mendelian disorder
A popular term for any genetic disease which follows simple mendelian patterns of inheritance; named after George Mendel who designed Punnet Squares; at the gene/allele level
What types of mendelian disorders are there?
- autosomal dominant inheritance
- autosomal recessive inheritance
- X-linked inheritance
- Mitochondrial DNA disorders
Describe autosomal dominant inheritance and provide example
a.Run in families and people with this condition in every generation
b.Males and females affected roughly in equal proportions
c.All forms of transmission present (male to female, male to male, female to male… etc.)
d.Dominant inheritance – 50%
e.Example – Polycystic Kidney Disease
i.Bilateral renal cysts, liver cysts, and an increased risk of intracranial aneurysms
What is autosomal dominant inheritance sometimes referred to as?
new dominant
Describe autosomal recessive inheritance and provide example
a.Males and females have the condition roughly in equal proportions
b.People with the condition are usually in one sibship in one generation
c.Consanguinity increases the number of individuals affected
d.Consanguinity – blood relation (first cousin, second cousin, …)
e.Recessive inheritance – 25%
f.Example – Cystic Fibrosis and Sickle Cell Anemia
i.High carrier frequency in European population
ii.Mutations in the CFTR gene
Describe X-linked inheritance and provide example
a.Males affected almost exclusively
b.The gene alteration can be transmitted from female carriers to sons
c.Affected males cannot transmit the condition to their sons
d.Carrier females may be mildly affected or fully affected due to skewed X inactivation
e.25% of having an affected child
f.Why are males affected by X-linked disorders? XY
i.Only 1 X chromosome
ii.Must express all X-linked genes
iii.Hemizygous
g.Most carrier (heterozygous) females are not affected by the X-linked disorders XX
i.The normal gene usually produces enough gene product to prevent the symptoms
h.Example – Duchenne Muscular Dystrophy
i. Affected males die in their 20’s, cannot reproduce
ii. Mutation may be inherited from mother or de novo (new mutation)
iii. High spontaneous mutation rate (1/3 cases)
Describe mitochondrial DNA disorders and provide example
a.All mitochondria are inherited from the mother through the egg
b.Mitochondria have their own circular DNA
c.Maternal inheritance – a mother affected, and ALL children affected to some extent
d.Mitochondrial Multisystemic disorders presents as:
i. Fatigue and low tone
ii. Cognitive dysfunction
iii. Feeding difficulties, constipation
iv. Cardiomyopathy
v. Limited eye movements
vi. Diabetes
vii. Some will have deafness
Describe chromosomal disorders
-Numerical chromosome anomaly
oError of meiosis (I or II) – results in aneuploidy (monosomy or trisomy) or triploidy
-Structural anomaly
oError in recombination
Describe nondisjunction
the failure of one or more pairs of homologous chromosomes or sister chromatids to separate normally during nuclear division, usually resulting in an abnormal distribution of chromosomes in the daughter nuclei
