Single Gene Disorders ✅

Question 1

What are most inherited genetic disorders caused by?

Answer 1

Mutations in a single gene

Question 2

What are hereditable genetic disorders also known as?

Answer 2

Mendelian disorders

Question 3

What does the pattern of inheritence of Mendelian disorders depend on?

Answer 3

• Chromosomal location of the gene
• Nature of mutation
• Degree of dysfunction of the gene required to cause disease

Question 4

What are genes?

Answer 4

The basic unit of inheritence

Question 5

What % of the DNA base pairs present in the human genome do genes account for?

Answer 5

1-2%

Question 6

What is the function of the remaining 98-99% of the DNA base pairs of the human genome?

Answer 6

Largely unknown

Question 7

What happens to genes when active?

Answer 7

They are transcribed into ribonucleic acid (RNA) molecules

Question 8

What happens once genes have been transcribed into RNA molecules?

Answer 8

(For most genes) RNA is translated into a protein that exerts the genes functions

Question 9

What facilitates transcription of genes?

Answer 9

A gene’s promoter region

Question 10

Where is a gene’s promoter region usually located?

Answer 10

Outside the coding region of the gene, upstream of the transcription start site

Question 11

What are the segments of a gene that are non-coding known as?

Answer 11

Introns

Question 12

What happens to the introns after transcription of RNA from DNA?

Answer 12

A process known as splicing occurs to remove the introns

Question 13

What are the sections of gene that will be translated (coding segments) known as?

Answer 13

Exons

Question 14

Where does translation of spliced RNA occur?

Answer 14

Ribosomes

Question 15

In what format is the RNA sequence ‘read’?

Answer 15

As codons

Question 16

What are codons?

Answer 16

Sets of 3 base pairs

Question 17

What happens to each codon as it is ‘read’?

Answer 17

It is bound by a tRNA molecule with a complementary base sequence, which carryins the amino acid specificed by the three-base sequence

Question 18

What does the binding of the appropriate tRNA molecule carrying amino acids to codons allow for?

Answer 18

The addition of the correct sequence of amino acids to the polypeptide chain that will form the mature protein

Question 19

How does the translational machinery know when to start and stop translation?

Answer 19

Specific codons

Question 20

What is translation? (Rearrange to before the codon card)

Answer 20

The process where the spliced RNA sequence is ‘read’

Question 21

Where in the process from DNA to protein production can mutations causing Mendelian disorders occur?

Answer 21

Anywhere

Question 22

What are the classes of genetic mutation?

Answer 22

• Loss of function mutation
• Gain of function mutation
• Triplet repeat expansion mutations

Question 23

What is the most common group of Mendelian mutation?

Answer 23

Loss of function mutations

Question 24

How do loss of function mutations act in many cases?

Answer 24

By causing the production of a truncated protein product

Question 25

What kind of loss-of-function mutations can result in the production of a truncated protein product?

Answer 25

• Nonsense mutation
• Splice mutation
• Frameshift mutation
• Deletion of single or multiple exons of a gene or the whole gene

Question 26

What is a nonsense mutation?

Answer 26

When a single nucleotide mutation generates a premature ‘stop; codon

Question 27

What is a splice mutation?

Answer 27

When a single nucleotide mutation disrupts splicing

Question 28

What is a frameshift mutation?

Answer 28

When deletion or duplication of the RNA sequence disrupts the codon reading frame of the translational machinery

Question 29

What is a missense mutation?

Answer 29

When single nucleotide variants result in the substitution of one amino acid for another in the protein

Question 30

Can missense mutations lead to loss of function?

Answer 30

Yes

Question 31

What is the result of the wide variety of ways that loss of function mutations can occur?

Answer 31

Disorders caused by loss of function can be caused by a correspondingly wide variety of mutations, often spread across the whole gene

Question 32

How do gain of function mutations cause disease?

Answer 32

By preventing inactivation of the protein’s normal function, or by giving the protein a novel function

Question 33

What kind of mutations are gain of function mutations most often?

Answer 33

Missense mutations

Question 34

What is the result of there being fewer ways that a gain in function mutation can happen compared to a loss of function mutation?

Answer 34

• Disorders caused by gain of function mutations are rarer

- Mutations often occur in a relatively narrow location within the gene itself (‘hot-spot’)

Question 35

What are triplet repeat expansion mutations?

Answer 35

A distinct class of mutation that result from the abnormal expansion of the size of the repetitive tract of a sequence

Question 36

What can happen when a repetitive tract of a sequence expands to be abnormally large?

Answer 36

It can affect gene expression or protein function to cause disease

Question 37

What can happen to triplet repeat expansion mutations with successive generations?

Answer 37

The size of the expansion can increase

Question 38

What happens with increasing expansion of triplet repeats with successive generations?

Answer 38

It can cause more severe, earlier onset disease

Question 39

What is the phenomenon where there is an expansion of triplet repeats with successive generations?

Answer 39

Anticipation