Genetics Flashcards
What are the 4 genetic principles?
Pleiotropy
Variable expression
Genome-environment interaction
Genetic heterogeneity
What is pleiotropy?
One gene can have multiple effects
What is variable expression?
The effect of a gene varies between individuals
What is genome-environment interaction?
The effect of a gene depends upon the environment
What is genetic heterogeneity?
Several different genes can have the same effect
Trisomy 21
- 47 XX/Y + 21
- characteristic round face, variable intellectual disability, congenital abnormalities of heart, epicanthic folds
Turner syndrome
- 45, X
- female, sterile, short often congenital abnormalities such as web of skin on neck, IQ within normal range
Klinefelter Syndrome
- 47, XXY
- male, sterile, small testes, usually tall due to long limbs, often normal IQ but may be impaired
Double Y Syndrome
- 47, XYY
- usually phenotypically normal male, often taller than average
Triple X Syndrome
- 47 XXX
- usually phenotypically normal female
Metacentric chromosome
Have the centromere in the centre, such that both sections are of equal length (1 & 3)
Submetacentric chromosome
Have a centromere slightly off centre leading to a slight asymmetry in the length of the two sections (4-12)
Acrocentric chromosomes
Have a centromere that is severely offset from the centre leading to one very short and on very long section (13,15,21,22)
Telocentric chromosomes
Have the centromere at the very end of the chromosome - not found in humans
Substitution
Occurs when one base pair is substituted for another
Nonsense
Occurs when one nucleotide is substituted for another and this leads to the formation of a premature stop codon
Missense mutaion
Occurs when one nucleotide is substituted for another and this leads to the formation of a codon that codes for a different amino acid
Synonymous mutaion
Occurs when a nucleotide is substituted but the same amino acid is produced anyway
Silent mutation
Occurs when a nucleotide is substituted, inserted or dell’età and does not have an observable effect of the organisms phenotype
Why do synonymous mutations occur?
Because multiple codons can code for the same amino acid
What is insertion?
Occurs when an extra base pair is added to a sequence of bases
What is deletion?
Occurs when a base pair is deleted from a sequence of bases
What is a frame shift mutation?
Occurs when a base pair is inserted or deleted which consequently disrupts the triplet reading frame of a DNA sequence
Amniocentesis
- 14-20 weeks
- needle used to obtain amniotic fluid that contains cells shed from the baby (contains baby’s DNA)
Chorionic villus sampling
- 10-12 weeks
- sample of chorionic villi cells are collected from the placenta
- these are formed when the fertilised egg divides (contain the same DNA as the baby)
What type of mutation causes cystic fibrosis?
Nonsense
Phenylketonuria
- missing hydroxylase enzyme: cannot break down phenylalanine
- symptoms: mental retardation, increased phenylalanine in the blood, fair skin and hair
What are inborn errors of metabolism?
Deficiency of an enzyme
What do inborn errors of metabolism lead to?
Accumulation of a substrate
Deficiency of a product
Disturbance of related pathways
