2: Genetics and disease

Question 1

When a gene is transcribed, (exons / introns) are removed.

Answer 1

introns

Question 2

What are introns?

Answer 2

Non-coding parts of a gene

Question 3

What are exons?

Answer 3

Coding parts of a gene

Question 4

Codons correspond to amino acids or ___.

Answer 4

stops

Question 5

Approximately which percentage of the genome is exons?

Answer 5

2-3%

Question 6

What do introns insulate genes from?

Answer 6

Promotors

Question 7

What technique is used to analyse DNA at the genome level?

Answer 7

Array CGH

Question 8

What techniques are used to analyse DNA at the level of individual base pairs?

Answer 8

PCR

Sanger Sequencing

Next Generation Sequencing (NGS)

Question 9

What is a mutation?

Answer 9

A genetic variation which causes disease

Question 10

What is a polymorphism?

Answer 10

A genetic variation which shows up in >1% of the population

not disease causing in and of itself

Question 11

PCR allows a geneticist to ___ one small piece of genome many times.

Answer 11

copy / amplify

Question 12

Codons with ___ base pairs will connect with one another.

Answer 12

complementary

Question 13

What technique is used to analyse DNA after PCR?

Answer 13

Sequencing

Question 14

What happens to the rate of transcription if there’s a promotor mutation?

Answer 14

No transcription or reduced transcription

Question 15

What happens to the quantity of protein expressed by a gene with a promotor mutation?

Answer 15

No protein expressed or less protein expressed

Question 16

A base change may introduce a new ___, cutting off the protein.

Answer 16

stop

Question 17

If a base change alters the amino acid sequence, what may happen to the protein expressed?

Answer 17

Different protein

or no protein

Question 18

How many base pairs does a missense mutation affect?

Answer 18

1

Question 19

In a missense mutation, what happens to the codon associated with the changed base?

What happens to the amino acid associated with the codon?

Answer 19

Different codon

Different amino acid

Question 20

What type of mutation involves a new base pair being shoved into a DNA sequence?

Answer 20

Insertion mutation

Question 21

What are the two categories of deletion mutation?

Answer 21

In frame

Out of frame

Question 22

Rather than Sanger sequencing, which tool is now available to sequence DNA?

Answer 22

Next generation sequencing (NGS)

Question 23

Finding a disease-causing mutation in a genome is difficult due to the number of ___ which already exist.

Answer 23

polymorphisms

Question 24

What is penetrance?

Answer 24

The likelihood of having a disease if you have a gene mutation

Question 25

What does **100% penetrance** indicate about a gene mutation?

Answer 25

It will **always** cause disease

Question 26

What is a **Mendelian Disorder**? How **penetrant** are these disorders?

Answer 26

A disease which is caused by a **change in a single gene** **High penetrance**

Question 27

What are the **three** categories of **Mendelian inheritance**?

Answer 27

**Autosomal dominant** **Autosomal recessive** **X-linked**

Question 28

In **autosomal dominant** inheritance, how many copies of a faulty gene are required to cause disease?

Answer 28

Only **1 copy**

Question 29

How many generations tend to be affected by **autosomal dominant** diseases?

Answer 29

**All of them**

Question 30

If one parent has an **autosomal dominant** gene for a disease, what are the chances of their child inheriting the disease?

Answer 30

**50%**

Question 31

How many copies of a faulty gene do you need to inherit an **autosomal recessive** disease?

Answer 31

**2 copies**

Question 32

How many generations tend to be affected by **autosomal recessive** diseases?

Answer 32

**Only one**

Question 33

What risk do you have of inheriting an **autosomal recessive** disease if both of your parents are carriers?

Answer 33

**25%**

Question 34

Which families have an increased risk of inheriting **autosomal recessive** diseases?

Answer 34

**Families in which there is inbreeding ('cosanguineous pairs')**

Question 35

Relative to the **X chromosome**, how many genes does the **Y chromosome** carry?

Answer 35

**Very few**

Question 36

Name a notable **X-linked recessive** disease.

Answer 36

**Haemophilia A & B** **Duchenne muscular dystrophy**

Question 37

In **X-linked recessive** disease, which chromosome carries the faulty gene?

Answer 37

**X chromosome**

Question 38

In terms of **X-linked recessive** disease, what is a **carrier**?

Answer 38

A female who has the allele on one of her X chromosomes but not the other, so she doesn't show major features of the disease

Question 39

How many **male children** of a **female carrier** will inherit an **X-linked recessive** disease?

Answer 39

**50%**

Question 40

How many **female children** of an **affected male** and **female carrier** with inherit an **X-linked recessive** disease?

Answer 40

**50%**

Question 41

If a **male** affected by **X-linked recessive disease** has male children with an unaffected non-carrier, how many of them will be affected?

Answer 41

**None of them**

Question 42

If a **male** affected with **X-linked recessive** disease has **female** children, how many of them will be carriers?

Answer 42

**All of them**

Question 43

Why may a **female carrier** of X-linked recessive disease show **mild symptoms** of that disease?

Answer 43

**Random X inactivation** - some of her cells will express the mutated gene

Question 44

Why does **random X inactivation** occur in females?

Answer 44

**Prevents double dose of X-linked alleles** (since the Y chromosome is inert)

Question 45

**Mendelian** diseases tend to be related to **(several small mutations / one high penetrance mutation)**.

Answer 45

**one high penetrance mutation**

Question 46

What kind of polymorphisms are responsible for variation between people in a population?

Answer 46

**Single Nucleotide Polymorphisms (SNPs)**

Question 47

What is a **Copy Number Variation (CNV)?**

Answer 47

**Extra or missing stretch of DNA**

Question 48

How **penetrant** are mutations in multifactorial disease?

Answer 48

**Low**

Question 49

Which lengthy studies can be done to figure out if a disease has a genetic component?

Answer 49

**Recurrence risk in siblings** **Twin studies**