Genetics Lecture 3 - Non-mendelian Inheritance Pt. 2 Flashcards
(23 cards)
What is non-Mendelian inheritance?
Anything that doesn’t fit into Mendel’s laws of single gene inheritance.
Myotonic dystrophy is due to an inheritance of what? What numbers of repeats correspond to what category?
Expanded CTG repeats. Normal: less than 35 Premutation: 35-49 Mild: 50-150 Classic: roughly 100-1000 Congenital: over 1000
Define polymorphism.
Benign difference in DNA amongst people.
Define anticipation.
Increase of severity or the earlier onset of an inherited disease in successive generations.
What causes Fragile X syndrome? What repeat numbers correspond to the different disease categories?
Inheritance of expanded CGG repeats in the FMR1 gene on the X chromosome. Normal is less than 45. Intermediate is 45-54. Premutation is 55-200. Full mutation is over 200.
Define mosaicism.
The presence of more than one cell line in an individual. Can be in somatic or germline.
Why are some disorders only seen in mosaic form? Name an example.
Non-mosaic forms are lethal. Example: Pallister-Killian: caused by tetrasomy 12p.
Gonadal mosaicism is usually due to what?
De novo mutations in the germ line. Parents are unaffected. Important for risk assessment for dominant disorders (example, non-little person starts having little people kids - achondroplasia)
Define genomic imprinting.
Modification of the maternal/paternal genetic contributions to the zygote (eg methylation). It is reset with each successive generation (each new person puts their own “stamp” on their germline DNA).
Define uniparental disomy. Do they always result in a phenotype? Name one disorder related to UPD.
When a child inherits two chromosomes from one parent. They don’t always result in a phenotype. Russell Silver Syndrome.
How is Prader-Willi inherited?
Several possibilities: paternal deletion of the critical region, maternal UPD, or an imprinting defect. The crucial thing to remember is that the Paternal chromosome is DELETED. It involves hyperphagia (pathological overeating). Paternal deletion is the most common way to get it.
How is Angelman syndrome inherited?
Several possibilities: maternal deletion of the critical region, paternal UPD, UBE3A mutation, or an imprinting defect. The crucial thing to remember is that the Maternal chromosome is DELETED. Maternal deletion is the most common way to get it.
What is trisomy 13 and some manifestations?
Patau syndrome - those that make it to birth may have polydactyly, ID and motor disorders, spinal defects, structural eye defects.
What is trisomy 18 and some manifestations?
Edward’s syndrome - often heart malformations are present like at LPCH, ID.
What is Klinefelter syndrome?
XXY (47, XXY). Males (phenotype may vary - genetically they are male) have decreased testosterone secretion. They are lanky, have less body hair, and wide hips.
What is a Barr body?
Its what an inactivated X chromosome looks like under the microscope.
What is Turner syndrome?
45, X. Genetically female, pts often have short stature, swelling, broad chest, low hairline, low-set ears, and webbed necks.
Define constitutional vs. congetical.
Constitutional = inherited genotype, congetical = physical traits at birth. Ex. Constitutional chromosome abnormalities may contribute to congenital birth defects.
What is trisomy 21?
Down syndrome. Mild to moderate ID, physical stuff you have seen.
What is lyonization?
It is random X chromosome inactivation and can explain how females would exhibit X-linked recessive disorders.
How to we inherit mitochondrial DNA?
From the mother only.
Nondisjunction in Meiosis I would result in what kind of disomy?
Heterodisomy.
Nondisjunction in Meiosis II would result in what kind of disomy?
Isodisomy.
