Inheritance Flashcards
How many generations should you aim for as a minimum when taking a family history?
3 generations
What is penetrance in relation to autosomal dominant inheritance?
The proportion of heterozygotes for a dominate a gene who express a trait, even if mildly
What is expressivity in relation to autosomal dominant inheritance?
The variation in severity of the phenotypic features of a particular gene
In which type of inheritance is population background information (e.g ethnicity) particularly useful? Why?
Autosomal recessive inheritance
Carrier frequency for different conditions can vary greatly between different populations
What is consanguinity? Which type of inheritance is it particularly important in?
The blood relation of two individuals
Autosomal recessive
How is mtDNA inherited?
Maternally
In mitochondrial inheritance, the offspring of an affected female…
Will all be affected
In mitochondrial inheritance, the offspring of an affected male…
Will not be affected
What is the use of paternal mitochondria?
Used to power tail of sperm in fertilisation and then lost
Most individuals affected by mitochondrial diseases have some normal and some mutated mtDNA, what is expression of the disease dependent on?
The burden of mutant vs normal mtDNA
Give an example of a mitochondria-related disease.
Leber’s hereditary optic neuropathy
Most common disease is not the result of mutations in single genes. It is….
Multifactorial
genes and non-genetic factors (e.g. Environment/behaviour) interact - on a spectrum
Give an example of a largely genetic (unifactorial) disease?
Duchenne muscular dystrophy
Give an example of a largely environmentally influenced disease?
Scurvy
Each individual has how many alleles of each gene?
2
What does homozygous mean?
What does heterozygous mean?
What does hemizygous mean?
In relation to alleles
Two alleles of a gene are the same
Two alleles of a gene are different
Only one allele exists for that gene on the x chromosome (only in males)
What is an example of co dominance in the human body?
Human ABO blood types
What is different between different blood types? What gene codes for these differences?
Different glycoproteins on surface of RBCs
Isoglutamin gene
What are the 3 different alleles for blood type? Which 4 blood types exist?
A, B and O
A, B, AB and O
Which alleles out of A, B and O are dominant over each other?
A is dominant over O
B is dominant over O
A and B show co-dominance
How is the unknown sex of an individual displayed when drawing a pedigree? How is a deceased individual displayed?
Diamond
Diagonal line through the symbol
By convention when drawing a pedigree the oldest child…
Is on the left of a line
By convention when during a pedigree each generation is… (2)
Numbered (roman numerals)
Given a separate line
In autosomal recessive inheritance, heterozygotes are…
Unaffected
In autosomal recessive inheritance, males and females are…
Equally affected
How can you recognise an autosomal recessive condition by a pedigree?
Males/females equally affected
Can skip generations
Disease ‘comes out of nowhere’
In autosomal dominant inheritance, heterozygotes are…
Affected
In autosomal dominant inheritance, males and females are…
Equally affected
Disease for autosomal dominant conditions is rarely found in the ______ state.
Homozygous
Every affected individual has a _____% chance of having affected children
(Autosomal dominant)
50%
Two heterozygotes have a _____% chance of having affected offspring.
(Autosomal recessive)
25% chance
Give an example of a autosomal recessive condition and an autosomal dominant condition.
Cystic fibrosis
Huntington’s disease
How can you recognise an autosomal dominant condition from a pedigree?
Males and females equally affected
Disease does not skip generations
Affected child will have at least 1 affected parent
Which individuals are affected by an X-linked recessive condition?
Homozygous females
Hemizygous males
X-linked recessive inheritance is more common…
In males
In x-linked recessive inheritance affected males _____ pass on trait to their sons
Cannot
In x linked recessive inheritance, what is the chance of a heterozygous female having an affected son?
50%
Give an example of an x-linked recessive disease.
Give an example of an x-linked dominant disease
Haemophilia A
Fragile X syndrome
How can x-linked recessive inheritance be recognised?
Males and females unequally affected
More common in males
Every affected female will have an affected father and a carrier mother at least
Every affected male will have at least a carrier mother
Which individuals are affected by X-linked dominant inheritance?
Hemizygous males and heterozygous females
In x-linked dominant inheritance, a heterozygous female has a ____% chance of having affected offspring.
50% chance
Why is Y linked inheritance so rare? How is it passed? What is an example?
Small chromosome - so very few genes
From father to son only
Y chromosome infertility
In which way is albinism inherited?
Autosomal recessive
Result of multiple genes
What is polygenic inheritance?
Where more than 1 gene is involved in producing a phenotype
What are linked genes?
Genes on the same chromosome
What are unlinked (not linked) genes?
Genes on different chromosomes
Congenital cataract shows which inheritance pattern?
Autosomal dominant
Tay-sachs disease shows which inheritance pattern?
Autosomal recessive
Haemophilia A shows which inheritance pattern?
X-linked recessive
Two genes that are close together on the same chromosome are _____ likely to be inherited together at meiosis
More likely to be inherited together
