Principles of Genetic Inheritance Flashcards
Lyonization (X-inactivation)
When one of a females X chromosomes become inactivated.
Mosiacism
Being composed of 2 cells that have different genotypes (and karyotypes).
Meiosis creates genetic diversity in 2 ways:
- Random segregation of homologues.
2. Crossing-over.
Meiotic errors (2)
- Polyploidy: presence of more than 2 complete sets of chromosomes.
- Aneuploidy: cells missing chromosomes or with an additional individual chromosome.
Turner Syndrome
45, XO karyotype.
Female without a Y. Causes ovarian hypofunction/premature ovarian failure. Unlikely to undergo puberty without hormone therapy. Most are infertile. Normal intelligence.
Klinefelter Syndrome
47, XXY. Can have variability in X numbers, which will increase symptoms.
Male. Some can have mild symptoms/none. Varying degrees of cognitive, social, behavioral or learning difficulties. Low T and small testes.
47, XX +21 Downs Syndrome
Most common. Increased risk with maternal age.
47, XX +13 Patau Syndrome
Severe developmental abnormalities. Most die within 1 week.
47, XX +18 Edwards Syndrome
Abnormal development. Most die within 1 year.
Genomic Imprinting
When, for some reason, one of the alleles is transcriptionally inactive. It is basically gene silencing, via methylation of the 5’ region of the gene. During meiosis, imprints are erased and new ones are set.
Prader-Willi Syndrome
Deletion of region of chromosome 15 on paternal chromosome. Short stature, small hands/feet, obesity, intellectual disability.
Angelman Syndrome
Deletion of region of chromosome 15 on maternal chromosome. Severe intellectual disability, seizures, ataxic gait.
Uniparental Disomy
2 chromosomes inherited from the same parent (will have parent specific imprinting).
Pleiotropy
Same genotype but multiple phenotypes.
Penetrance
Frequency that a gene manifests itself (i.e. how many people with that genotype express that phenotype?)
