inheritance patterns Flashcards
what are the 3 categories of genetic disorders
chromosome abnormalities
single gene disorders
multifactorial & polygenic disorders
give 3 examples of multi factorial and polygenic disorders
spina bifida
cleft lip
palate
define aneuploidy
the condition of having an abnormal number of chromosomes in a haploid set
define cytogenetics
the study of inheritance in relation to the structure and function of chromosomes.
what are the 6 common structural anomalies in clinical cytogenetics
- translocations
- inversions
- deletions
- duplications
- ring chromosome
- fragile site
what is chromosome 22q11 deletion syndrome
a disorder caused when a small part of chromosome 22 is missing
what are the clinical features of chromosome 22q11 deletion syndrome
- characteristic facial features
- congenital heart disease
- palatal abnormalities
- learning difficulties
- psychiatric problems
- immunodeficiency
- hypocalcemia
- renal abnormalities
what 3 laws did Mendel come up with
- segregation
- dominance
- independent assortment
what does mendels law dominance mean
every gene has 2 alleles that code for a trait
in heterozygotes 1 allele is dominant meaning it will always show, one is recessive and is masked by the dominant one
what does mendels law segregation mean
allele pairs separate/segregate randomly from each other during meiosis - each cell has a single allele for each trait
what does mendels law independent assortment mean
traits are transmitted to offspring independently of one another
what does mendelian inheritance refer to
autosomal and sex linked
dominant and recessive
what does non-mendelian inheritance refer to (4)
imprinting
mitochondrial inheritance
multifactorial
mosaicism
define autosome
any chromosome, other than the sex chromosomes (X or Y), that occurs in pairs in diploid cells
define recessive
manifest only in homozygotes
define allele
one or more alternative forms of a gene at a given location (locus)
define homozygous
presence of identical alleles at a given locus
homozygotes are affected
define hetertozygotes
presence of 2 different alleles at a given locus
heterozygotes are unaffected and are usually referred to as carriers
define allelic heterogeneity
when different mutations within the same gene result in the same clinical condition
this means an individual with an autosomal recessive condition may be a compound heterozygote for 2 different mutations
what are 3 features of autosomal recessive inheritance
- male and females affected in equal proportions
- affected individuals only in a single population
- parents can be related ie consanguineous
what is the most common autosomal recessive disease
cystic fibrosis
what does cystic fibrosis affect
mainly lungs and gut
but can also affect other systems
whats the most common cystic fibrosis mutation
change in F508
how many cystic fibrosis mutations are detected by standard carrier testing
top 29
what kind of test is sweat testing
diagnostic
define consanguinity
reproductive union between two relatives
define autozygosity
homozygosity by descent ie inheritance of the same altered allele through two branches of the same family
how do you show consanguinity on a pedigree diagram
double lines
what is the risk of children having autosomal recessive disease if parents are carriers
1 in 4
what is the risk of healthy siblings having autosomal recessive disease
2 in 3
in what kind of families ar autosomal recessive diseases more common
consanguineous
what are 4 features of autosomal dominant inheritance
- male and females affected in equal proportions
- affected individuals in multiple generations
- transmission by individuals of both sexes, to both sexes
what are autosomal dominant conditions
they are manifest in the heterozygous state so only one affected gene is needed
define penetrance
the percentage of individuals with a specific genotype showing the expected phenotype
define expressivity
refers to the range of phenotypes expressed by a specific genotype
define recurrence risk
a statistic that estimates the probability that a condition present in one or more family members will recur in another relative in the same or future generations.hhhh
define anticipation
The signs and symptoms of some genetic conditions tend to become more severe and appear at an earlier age as the disorder is passed from one generation to the next
this is usually due to expansion of unstable triplet repeat sequences
define somatic mosaicism
genetic faults present in only some tissues in the body
define gonadal (germline) mosaicism
genetic fault present in gonadal tissue
generally more common in X linked disorders
define late onset
when a condition is not manifest at birth, esp in relation to other people with the condition.
eg hypertrophic cardiomyopathy
define sex limited
a condition inherited in an autosomal domincant pattern that seems to affect one sex more than another
eg BRCA1/2
define predictive testing
testing for a condition in a pre-symptomatic individual to predict their chance of developing condition
what usually confirms autosomal dominant inheritance
male to male transmission
because a father passes on his Y chromosome to a son, male-to-male transmission cannot be seen with an X-linked trait
what are 3 factors of X-linked inheritance
- usually, only males affected
- transmitted usually through unaffected females
-no male-to-male transmission - an affected male cannot have affected sons, but all his daughters will be carriers
define lyonization (X inactivation)
normally one of the two X chromosomes in every cell of a female individual is inactivated during embryonic development.
what is genomic imprinting
an epigenetic (non genetic influence on gene expression) phenomenon that causes genes to be expressed in a parent of origin-specific matter
the process by which only one copy of a gene in an individual (either from their mother or their father) is expressed, while the other copy is suppressed.
what causes PWS disease
missing genetic material in a group of paternal genes on chromosome number 15
what causes angelman syndrome
loss of function of maternal UBE3A due to point mutation or deletion
so 2 paternal copies are inherited instead of 1 maternal and 1 paternal
define homoplasmy
a eukaryotic cell whose copies of mitochondrial DNA are all identical (identically normal or have identical mutations)
define heteroplasmy
the presence of more than one mtDNA type in an individual
identifies mutations which affect only a proportion of the molecules in a cell
level of heteroplasmy varies between cells in the same tissue or organ, from organ to organ within the same person and between individuals in the same family
atdefine heteroplasmy
the presence of more than one mtDNA type in an individual
identifies mutations which affect only a proportion of the molecules in a cell
level of heteroplasmy varies between cells in the same tissue or organ, from organ to organ within the same person and between individuals in the same family
what is mtDNA
DNA found in mitochondria instead of nucleus
all of it comes from our mothers - its not a mix of parents
usually identical to mothers mtDNA
what is a mitochondrial genetic disease
a group of disorders caused by dysfunctional mitochondria
