Genetic Inheritance of Disease Flashcards
how much of genome is non-coding?
how many genese make up the coding part of genome?
- 98% is of human genome is non-coding
2% has 21 000 genes
what are a) varients? b) polymorphisms? c) mutations
a) varients: changes in genome that do no affect human health
b) polymorphisms: genetic mutations that are very common in the human genome, may or may not contribute to disease (more than 1% freq)
c) mutations: less that 1% frequency in human populations and generally affect normal physiology
what are two ways can classify a mutation?
- inherited or acquired
- rare or common
what is a mendelian or monogenic disorder?
what is a multifactorial disorder?
what is a complex disorder?
mendelian / monogenic : a disease or trait determined by a single gene
multifactorial: disease / trait determined by a small no. of genes (oligogenic trait), or a large number of genes with individually small effects (polygeneic traits)
complex: disease or trait determined by a large number of genes and their effects is also altered by environmental factors (e.g. Diabetes)
what is an allele?
alternative version of the same gene. one is inherited from the mother, one is from the father and can vary in sequence.
homozygous: both alleles are same from parents
heterozygous: if the alleles at a specific postion on a gene are not identical
what does the mode of inheritance in Mendelian traits depend on?
1. whether the gene is on an autosomal or sex chromsome
2. whether the trait is determined by a dominant or recessive genotypes
why is idea the of heterozygosity / homozygosity lost for sex linked mendelian traits?
because you dont have two copies of the same gene (X / Y) are different.
what are the 5 main types of modes of inheritance?
autosomal dominant
autosomal recessive
X-linked dominant
X-linked recessive
Y-linked
which offspring from autosomal dominant parents will not inherit disease?
homozygous recessive children.
(if you have allele you get the trait)
what can modify the expression of autosomal dominant diseases?
(linked:) what is variable expressibivity?
what is anticipation?
- new mutation: sporadic de novo cases
2. variable penetrance: genetic background or the environment can cause difference in disease penetrance
- variable expressivity: variation is severity of symptoms (genes could be expressed at different level)
anticipation: disease manifests at a younger age in successive generations
(penetrance - proportion of individuals carry a disease causing allele)
(expressivity - extent to which a genotype exhibits its phenotypic expression)
give example of autosomal recessive disease (x3)
which is more common - autosomal dom or autosomal rec?
phenylketonuria (PKU)
sickle cell disease
CF
autosomal recessive is more common
how can you tell from a pedigree if a disease is autosomal recessive?
- more carriers than affected
- not sex linked (equally effects m/f)
which offspring are affected x-linked dominant disease is given by:
a) affected mother
b) affected father
x-linked dominant:
if mother is affected: can pass onto boy or girl offspring
if father is affected: _pass onto all daughters, not sons (_gives son Y chr - unaffected)
give 3 x-linked dominant traits
goltz syndrome
x-linked poryphyria
fragile x-syndrome
on a pedigree, which shape is male and which is female?
male - square
female - circle
what type of mutation is this ?
de novo
what is the grey box in this and what type of diseas e
autosomal dom
grey - anticipation
describe difference between frequency found and how strong the effects are of monogenic, oligogenic and polygenic diseaseS?
can generally understand whether a trait is more likely to be
monogenic: v. rare but strong effects & env effect small,
oligogenic: still rare (>0.1 to <5%). moderate effects.
polygenic common variants (>5%). weak effects. dont produce disesae in isolation. env has bigger effect
