Genome

Question 1

What are the nucleotides in DNA and RNA

Answer 1

Purine: Adenine, gunaine

Pyramidine: Cytosine thiamine uracil

DNA ATCG
RNA AUCG

Question 2

Structure of DNA

Answer 2

Sugar phosphate group linked by phosphodiester bond

Triphosphate
Deoxyribose sugar and nucleotide

Double helix structure

Antiparalle strands

Annealed by specific base pairing with hydrogen bonds

Question 3

How is DNA packaged in nucleus

Answer 3

DNA winds into nucleosome spools (146 base pairs) wound around histone protein

Nucleosome coiled into solenoid

Solenoid forms loops that attach to scaffold - heterochromatin

Scaffold plus loops arrange into giant supercoil

At metaphase chormatin condensed max

Chromomsome formed of sister chormatids connected at centromere - p and q arms

Question 4

How many chromosomes in humans?

Answer 4

46
22 autosomal pairs
1 sex chormosome pair

1 to 22 in order of decreasing size

Question 5

What is Mendelian inheritance

Answer 5

Pattern of inheritance depends on location of gene

Five patterns
AD
AR
XD
XR
Y

Question 6

What is penetrance?

Answer 6

Proportion of individuals that carry a gene that actually express it

Question 7

What is expressivity

Answer 7

Variation in phenotype amongst individuals that carry the same gene

Question 8

What is imprinting

Answer 8

Gene is only expressed depending on its parental origin e.g. inulin like growth factor 2 only expressed when inherited from father allele

Question 9

What is anticipation

Answer 9

Symptoms of genetic disorder become apparent at an earlier age

e.g. Huntington’s disease - unstable gene undergoes trinucleotide repeat that leads to gain of function in the resultant protein - increases with each passing gemeration

Question 10

Sickle cell diases? BEta thalassaemia? Phenylketonuria? HAemochromatosis?

Answer 10

Autosomal recessive

Question 11

G6PD deficiency
HAemophilia A
DMD

Answer 11

X-linked recessive

Question 12

What conditions show anticipation

Answer 12

Trinucleotide repeat

Myotonic dystrophy
Huntington’s

Question 13

What conditions show imprinting

Answer 13

Differential expression of genetic material depending on the parent from whom it has been inherited

Prader Willi
Angelman syndrome

Question 14

What is uniparental disomy?

Answer 14

Duplication of chromosome from one parent and loss of homologue from the other parent

Question 15

Mitochondrial inherited condition

Answer 15

Leber’s hereditary optic neruopathy

Question 16

What is mosaicism

Answer 16

Presence of mulitple cell lines within an individual from a single zygote

Question 17

What is germline mosaicism

Answer 17

Abnormal cell line confined to gonads - result in unaffected parents producing more than one child with an AD condition

Question 18

What is somatic mosaicism?

Answer 18

MAternal or paternal chormosome is inactivated in each somatic cell

Each of that cell’s progeny will have inactivation

Unusually mild symptoms in AD conditions