genetics Flashcards
what is penetrance
the likelihood of having a disease if you have a gene mutation
what are mendelian disorders
a disease that is predominantly caused by a change in a single gene
are mendelian disorders high or low penetrance
high penetrance
autosomal dominant inheritance
one copy of the faulty allele is sufficient to cause the disease
what is the chance of an affected person passing on the pathogenic variant to a child in autosomal dominance
50%
who is more likely to be affected by autosomal dominant disorders
males and females are equally likely to be affected
autosomal recessive inheritance
affected person has 2 faulty alleles
what makes autosomal recessive inheritance more likely
consanguineous parents
risk of a child being affected by an autosomal recessive disorder
25%
risk of a child being a carrier of an autosomal recessive disorder
50%
x-linked inheritance
the pathogenic variant is found on the x chromosome
differences in gender in x-linked inheritance with one pathogenic allele
females don’t show major clinical features
males with a single faulty allele will be fully affected
outcomes for children of a female carrier of x-linked disorder
25%
- unaffected daughter
- carrier daughter
- unaffected son
- affected son
outcomes for children of a male carrier of x-linked disorder
all daughters will be carriers and all sons will be affected
what causes females to not be so affected by x-linked inheritance
x-inactivation
what are the 3 main types of chromosomes
submetacentric
metacentric
acrocentric
how do sister chromatids attach
at the centromere
describe a metacentric chromosome
telomere is close to the middle, with a shorter p arm and a longer q arm
describe an acrocentric chromosome
centromere at one end, with only satellite DNA on the short p arm
during what phase of the cell cycle are chromosomes visible
during metaphase in mitosis
what is aneuploidy
there is a whole extra or missing chromosome
what is translocation
rearrangement of chromosomes
chromosomal abnormality in down syndrome
47XY +21
chromosomal abnormality in edwards syndrome
47 XY +18
chromosomal abnormality in turner syndrome
45 X
chromosomal abnormality in klinefelter syndrome
47 XXY
what is robertsonian translocation
2 acrocentric chromosomes become joined end to end
reciprocal translocations
swap of genetic material between chromosome arms
chromosomal abnormality in DiGeorge syndrome
chromosome deletion
what is FISH
fluorescence in situ hybridisation
role of FISH
allows you to look for the presence of a specific chromosomal region
give an example of a disease you can look for using FISH
cancer abnormalities
what is the first line chromosome test
array CGH
what does aCGH detect
chromosome imbalance
what is a weakness of aCGH
doesn’t detect balanced rearrangements
what is mosaicism
different cells have a different genetic constitution
role of PCR
allows us to select one small piece of the human genome and amplify it
what is a mutation
a genetic variation that causes a disease
what is a polymorphism
a genetic variation that is prevalent in the population and not, in itself, disease causing
what does p. mean
the change in the peptide sequence
what does c. mean
the change in the mature mRNA sequence
