E9 Basic genetics

Question 1

where does the evidence for importance of genetics in disease come from?

Answer 1

• studying identical and non-identical twins
• studies of identical twins separated at birth

Question 2

how are genetic diseases becoming both preventable and treatable?

Answer 2

preventable
- human embryos have been edited to stop genetic disease
- gremlin editing isn’t allowed in the UK due to moral beliefs

treatable
- Nusinersen is an antisense oligonucleotide drug for spinal muscular atrophy

Question 3

define trait

Answer 3

• inheritable characteristics
• eg. height (complex trait), hair colour (less complex, especially for red hair)

Question 4

define phenotype

Answer 4

• variant of characteristic in individual
• eg. for hair colour, the phenotypes are brown, black, red, blonde etc.

Question 5

define mutation

Answer 5

change in a gene

Question 6

define allele

Answer 6

one of the different variants of a gene

Question 7

define polymorphism

Answer 7

• the specific differences in the DNA sequence between alleles
• eg. deletion of a C base

Question 8

define genotype

Answer 8

• combination of alleles in the DNA sequences of an individual
• although formally harmful mutations are also polymorphisms, the term is usually used for normal variation
• a lot of genetic variation has no detectable consequences eg. silent mutations or mutations in introns

Question 9

what are people with Aa genotype called?

Answer 9

carriers

Question 10

why do recessive alleles on the X chromosome affect men more than women?

Answer 10

women have 2 X chromosomes so they must be homozygous recessive to have condition but men only need one copy of recessive allele to have condition

Question 11

where are mitochondrial mutations inherited from?

Answer 11

the mother only

Question 12

describe Huntington’s disease genetics

Answer 12

• autosomal dominant
• mutated allele is always expressed if it is present

Question 13

describe cystic fibrosis genetics

Answer 13

• autosomal recessive
• need to be homozygous recessive to be expressed

Question 14

describe Duchenne muscular dystrophy genetics

Answer 14

• X-linked recessive
• males need one copy of Duchenne’s allele to be affected
• females need 2 copies (homozygous)

Question 15

describe mitochondrial genetics

Answer 15

• most mitochondrial proteins are encoded in the nucleus
• mitochondria have a small genome on a circular chromosome of their own
• multiple mitochondrial genomes are inherited from the mother in the egg

Question 16

how do Mendelian genetics and human genetics differ?

Answer 16

• Mendelian makes things look pretty simple in principle
• human genetics have many complicating factors in reality

Question 17

what is incomplete penetrance?

Answer 17

• having a particular gene variant makes it more likely but not certain that you’ll have the disease

Question 18

state a disease that involves complete penetrance

Answer 18

cystic fibrosis

Question 19

what is meiotic recombination and what does it do?

Answer 19

• reshuffles gene variants
• this is due to crossing over in meiosis I
• the closer 2 genes are together on their chromosome, the less likely it is that they will be separated because it’s less likely that the chiasmata will be between the 2 genes

Question 20

what happens in genetic mapping?

Answer 20

• an inherited trait is attributed to a certain gene
• based on linkage, polymorphisms are more likely to be inherited together if they’re located close to eachother

Question 21

what is Next Generation Sequencing doing?

Answer 21

• speeding up the process of genome sequencing enormously
• bringing down the cost of whole genome sequencing

Question 22

what are the 2 bottlenecks making the genomic revolution slower than advertised?

Answer 22

• obtaining enough DNA samples
• analysis

Question 23

describe the bottleneck slowing down the genomic revolution of obtaining enough DNA samples

Answer 23

• need enough DNA samples with good clinical data and patient permission

blood tests
GDPR etc

Question 24

describe the bottleneck slowing down the genomic revolution of analysis

Answer 24

• need to analyse the huge amount of data