Genetics

Question 1

What are the 4 genetic principles?

Answer 1

Pleiotropy
Variable expression
Genome-environment interaction
Genetic heterogeneity

Question 2

What is pleiotropy?

Answer 2

One gene can have multiple effects

Question 3

What is variable expression?

Answer 3

The effect of a gene varies between individuals

Question 4

What is genome-environment interaction?

Answer 4

The effect of a gene depends upon the environment

Question 5

What is genetic heterogeneity?

Answer 5

Several different genes can have the same effect

Question 6

Trisomy 21

Answer 6

• 47 XX/Y + 21

- characteristic round face, variable intellectual disability, congenital abnormalities of heart, epicanthic folds

Question 7

Turner syndrome

Answer 7

• 45, X

- female, sterile, short often congenital abnormalities such as web of skin on neck, IQ within normal range

Question 8

Klinefelter Syndrome

Answer 8

• 47, XXY

- male, sterile, small testes, usually tall due to long limbs, often normal IQ but may be impaired

Question 9

Double Y Syndrome

Answer 9

• 47, XYY

- usually phenotypically normal male, often taller than average

Question 10

Triple X Syndrome

Answer 10

• 47 XXX

- usually phenotypically normal female

Question 11

Metacentric chromosome

Answer 11

Have the centromere in the centre, such that both sections are of equal length (1 & 3)

Question 12

Submetacentric chromosome

Answer 12

Have a centromere slightly off centre leading to a slight asymmetry in the length of the two sections (4-12)

Question 13

Acrocentric chromosomes

Answer 13

Have a centromere that is severely offset from the centre leading to one very short and on very long section (13,15,21,22)

Question 14

Telocentric chromosomes

Answer 14

Have the centromere at the very end of the chromosome - not found in humans

Question 15

Substitution

Answer 15

Occurs when one base pair is substituted for another

Question 16

Nonsense

Answer 16

Occurs when one nucleotide is substituted for another and this leads to the formation of a premature stop codon

Question 17

Missense mutaion

Answer 17

Occurs when one nucleotide is substituted for another and this leads to the formation of a codon that codes for a different amino acid

Question 18

Synonymous mutaion

Answer 18

Occurs when a nucleotide is substituted but the same amino acid is produced anyway

Question 19

Silent mutation

Answer 19

Occurs when a nucleotide is substituted, inserted or dell’età and does not have an observable effect of the organisms phenotype

Question 20

Why do synonymous mutations occur?

Answer 20

Because multiple codons can code for the same amino acid

Question 21

What is insertion?

Answer 21

Occurs when an extra base pair is added to a sequence of bases

Question 22

What is deletion?

Answer 22

Occurs when a base pair is deleted from a sequence of bases

Question 23

What is a frame shift mutation?

Answer 23

Occurs when a base pair is inserted or deleted which consequently disrupts the triplet reading frame of a DNA sequence

Question 24

Amniocentesis

Answer 24

• 14-20 weeks

- needle used to obtain amniotic fluid that contains cells shed from the baby (contains baby’s DNA)

Question 25

Chorionic villus sampling

Answer 25

• 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)

Question 26

What type of mutation causes cystic fibrosis?

Answer 26

Nonsense

Question 27

Phenylketonuria

Answer 27

• missing hydroxylase enzyme: cannot break down phenylalanine
• symptoms: mental retardation, increased phenylalanine in the blood, fair skin and hair

Question 28

What are inborn errors of metabolism?

Answer 28

Deficiency of an enzyme

Question 29

What do inborn errors of metabolism lead to?

Answer 29

Accumulation of a substrate
Deficiency of a product
Disturbance of related pathways