Mendelian Inheritance of Human Disease

Question 1

What is a genes locus?

Answer 1

The precise position of the gene on the chromosome

Question 2

What is an allele?

Answer 2

Alternative forms of a gene

Question 3

What is a genetic disease?

Answer 3

One caused by a change in the genes.

Question 4

What do promotor and splice site sequence change mutations cause?

Answer 4

Stop transcription or cause abnormal splicing

Question 5

What can some missense mutations do?

Answer 5

Make a protein work faster

Question 6

What is a wild type?

Answer 6

An individual having normal DNA sequences

Question 7

What is a stop mutation?

Answer 7

Where a premature stop codon is introduced so the rest of the sequence is not transcribed or translated

Question 8

What is a missense mutation?

Answer 8

Where there is a different base in the DNA sequence (substitution) but it only affects the codon it is in, the codons after the mutation are unaffected.

Question 9

What is an Insertion mutation?

Answer 9

Where a base is inserted into the DNA sequence, casing all the codons after the point of mutation to be affected

Question 10

What is a deletion out of frame mutation?

Answer 10

Where a single base is deleted and so all codons after the point of mutation are affected

Question 11

What is a deletion in frame mutation?

Answer 11

Where a whole codon is deleted but all codons after the mutation stay the same

Question 12

What is a triple expansion mutation?

Answer 12

Where a codon is repeated

Question 13

What is mendelian inheritance?

Answer 13

A change in a SINGLE gene sufficient to cause clinical disease

Question 14

What is non-mendelian inheritance

Answer 14

Everything else including multifactorial diseases (More than one genetic risk factor)

Question 15

Describe the percentage of DNA shared by 1st, 2nd and 3rd degree relatives

Answer 15

1st - 50%. (100 % if are identical twins)
2nd - 25%.
3rd - 12.5%

Question 16

What is autosomal dominant mutations?

Answer 16

A mutation on any chromosome that isn’t a sex chromosome that makes the person affected. (only need one copy of mutation to become affected)

Question 17

What is allelic heterogeneity?

Answer 17

Where different mutations in the same gene can cause the same disease

To do a gene test you need to know approximately where to look

Question 18

What is locus heterogeneity?

Answer 18

Where the same disease may be caused by mutations in one of several genes

To do a gene test you need to know approximately where to look

Question 19

Describe features of autosomal dominant mutations

Answer 19

Disease will be seen in every generation however the severity of disease can be variable. Males and females are equally likely to be affected. 50% chance of passing it too offspring

Question 20

What is autosomal recessive

Answer 20

A mutation where you need both chromosomes to have the mutation to be afffected

Question 21

Describe some features of autosomal recessive mutations

Answer 21

Often only one generation is affected. 25% chance of passing it onto offspring. Increased likelihood in consanguineous families.

Question 22

What is an X-linked disease?

Answer 22

A mutation on the X chromosome that causes clinical disease. It is often recessive

Question 23

Describe features of an X-linked recessive inheritance

Answer 23

For female carriers - Half of male children affected and half of daughters will be carriers.

For affected male - All sons will be normal but all daughters will be carriers

Question 24

What does nonpenetrance mean?

Answer 24

Failure of a genotype to manifest

Question 25

Variable expression

Answer 25

Where different family members may show different features of a disorder

Question 26

Where are nonpenetrance and variable expression seen more often? And why?

Answer 26

In dominant conditions due to influecnce of other genes and environment, as well as chance

Question 27

Describe features of mitochondrial DNA

Answer 27

Contains important genes for mitochondrial metabolic pathways and ribosomal RNA, inherited exclusively maternally and point mutations and deletions can occur

Question 28

Describe features of mitochondrial inheritance

Answer 28

Diseases in mitochondrial DNA is rare, is is via maternal transmission only and sons and daughters are equally affected.

Question 29

Muscle Biopsy

Normal and Henry

Answer 29

Question 30

X linked recessive

diagram

Answer 30

Question 31

Features of Duchenne Muscular Dystrophy

Answer 31

Question 32

X Linked Disaese

diagram

Answer 32

Question 33

X linked recessive

diagram

Answer 33

Question 34

Hereditary Haemorrhagic Telangiectasia (HHT2)

Answer 34

Question 35

Hereditary Haemorrhagic Telangiectasia (HHT1)

Answer 35

Question 36

Features of mutations in Fibrillin (Marfan´s Syndrome)

Answer 36

Question 37

Mutations and their effects summary

Answer 37