Genetic Inheritance Flashcards
(48 cards)
What are the key factors in spotting autosomal dominant?
Male to male inheritance
Incomplete penetrance
Variable expression
How do you predict the inheritance risk of autosomal dominant inheritance?
1/2 X penetrance
What are the key points in pointing out autosomal recessive conditions?
Usually one generation affected
Parents both asymp. Carriers
How do you predict the inheritance risk of someone inheriting an autosomal recessive condition?
Mums carrier risk X dads carrier risk X 1/4
What are the key points in spotting X linked recessive conditions?
Usually only men affected
Females are asymp. Carriers
All daughters of affected men are carriers
Can be caused by mutation so not necessarily inherited
What is mosaicism?
Mixture of cells in a person with different amount of chromosomes
What is the karyotype for mosaic Down syndrome? (14 and 21 chromosome)
47, XX +21/46
Why does mosaicism occur?
Due to post-zygotic errors in mitosis (no disjunction or trisomy rescue)
What is trisomy rescue?
Where a fertilised ovum containing 3 copies of a chromosome loses one to form normal diploid chromosomes
Give an example of a somatic mosaicism condition
Segmental neurofibromatosis
What is germline mosaicism?
Mutated cells only present in a persons gonads (won’t have condition but can pass it to child)
Why is reoccurrence of a De novo mutation not 0%?
Germline mosaicism
Non-paternity may also be considered
What is non-disjunction?
Failure of homologous chromosomes to separate during cell division
What is the trisomy karyotype for Down’s syndrome?
47, XX + 21
What is a reciprocal translocation?
Where sections of non-homologous chromosomes separate and attach at different points
What is a robertsonian translocation?
Translocation caused by breaks at or near the centromeres of two acrocentric chromosomes
What is the karyotype of of a 14 and 21 robertsonian translocation?
45, XY, der(14;21)
What are the patterns of chromosomes that cause Down’s syndrome?
Trisomy 21 - 47, XX + 21
Robertsonian translocation
Mosaicism
What chromosome set has 100% chance of passing on Down’s syndrome?
Translocation trisomy 21 or if two T21 pregnancies
What is pseudo dominant inheritance?
Where a recessive condition mimics dominant inheritence pattern?
Who can have X-linked dominant lethal conditions?
To men they are lethal
To women they are severe
Give an example of a x-linked dominant lethal condition
Incontinentia pigmenti
Why in a certain skin condition might a woman have skin affected and normal skin?
Somatic mosaicism
X-linked condition but in each cell one X chromosome is inactive - random in each cell
What is genomic imprinting?
Epigenetic phenomenon where genes are expressed in a parent of origin specific manner
