intro to genetics Flashcards
automonal recessive
autosomal recessive - 2 copies required from either parent
parents may be unaffected but carry the gene
not always seen in every generation
carriers are not usually affected
more common in coansguies families
recurrence risks for offspring is 25% of carriers
x linked dominant
males and females equally affected
- males more severely
no male to male transmission
affected females can have affected sons and daughters
offering of an affected female have 50% chance oof being afffected
individuals with downs
Most individuals (95%) have 3 free copies of chromosome 21
Mostly of maternal origin and occur during meiosis 1
5% 1 copy is translocated (chromosome 14 or 21)
2-4% mosaicism with normal cell lone
clinical features of downs
Learning difficulties
Short stature
Flat facial profile
Hearing loss
Congenial heart defects
Gastrointestinal
Early Alzheimer
what are the features of turners syndrome
deleted x syndrome
De Novo Mutations – Random event
Many Pregnancies do not make it to full-term
People born with Turner’s syndrome are not able to reproduce
50 in 100 000 newborn girls
Heart problems – Aortic Coarctation
Learning difficulties – Neurocognitive defects
Various systemic problems
Short Stature
Learning difficulties and low IQ
klinefeter
1:500 to 1:1000 male live births
Extra X chromosome
Hypogonadism and affecting male sexual development
Associated risk for other congenital malformations, psychological problems, learning difficulties compared to siblings and other medical problems.
Tall
Not able to reproduce
Treat with testosterone
xyy
Extra Y chromosome
Male 1/1000 Live birth
Found incidentally in pre-natal diagnosis
Increased growth rate – Tall
Have normal sexual development and fertility
IQ not generally reduced but some evidence to show reduction in comparison to siblings
triple x (trisomy x)
Additional X Chromosome
1 In 1000 newborn girls
Taller than average
Normal development and able to reproduce
Increased risk of learning difficulties and SPLD problems
Could also have some motor deficits and emotional problems
Variable presentation
translocation
Translocations: piece of one chromosome breaks off and attaches to another
Balanced
Unbalanced – usually inherited from a parent with balanced translocation and often end up with array of symptoms depending on the type of translocation
what is Williams (beaten syndrome)
Sporadic Autosomal Dominant inheritance
Hemizygous deletion of 1.5 to 1.8Mb on Chromosome 7
Williams et al (1961)
Suprvalvular aortic stenosis
Learning difficulties
Changes in Facial Features
Short Stature
Stellate pattern of iris, strabismus and VA deficits
cri- du - chat syndrome
Terminal Deletion of the short arm of chromosome 5
First described Lejeune et al (1963)
Microcephaly
Round face
Hyptertelorism
Epicanthal folds
Low-set ears
Hypotonia
Development delay
features of fragile x
Macrocephaly
Distinctive facial features
Skeletal problems
Learning difficulties and psychological problems
Autistic features
Seizures
caused by mutation in the FMR1 gene
trinucleotide
permutations
males more severely affected as only one X chromosome
female carriers can also be affected by less severely
RETT syndrome
mutations in the MEcp2 syndrome
Rare versions can be caused by mutations in FOXG1 (Chromosome 14)
Neurodevelopment disorders that occurs most exclusively in females
Arrested development between 6-18m followed by regression
Can occur in males who have two X Chromosomes (Klinefelter’s Syndrome), otherwise lethal in males
what is imprinting
Imprinting is the differential expression of genetic material depending on whether it has been inherited from the mother or father – one can be more damaging than the other.
Angelman
70% result from a de novo maternal deletions involving Chromosome 15
2% inheriting two copies of Chromosome 15 from Father
25% specific mutation in E3A gene
Neurodevelopment disorder with learning difficulties, motor problems, Speech and language difficulties
Happy disposition
