9. Human genetics(1)

Question 1

What percentage of embryos have chromosomal defects?

Answer 1

50%

Question 2

What percentage of newborn babies have a congenital disorder?

Answer 2

5%

Question 3

what percentage of clinical conceptions terminate due to chromosomal abnormalities?

Answer 3

8%

Question 4

What percentage of live births display a chromosomal abnormally?

Answer 4

0.1%

Question 5

How does a mitochondrial disorder come about?

Answer 5

Mutations within mtDNA result in a number of mitochondrial disorders
(mutation disorder don’t follow mendelian patterns of inheritance)

Question 6

Describe single gene disorders in terms of :

No of genes:
Pattern of inheritance: 
Rarity:
Penetrance:
Tests:

Answer 6

No of genes - Disease allele at a single gene
Pattern of inheritance - Mendelian
Rarity: Individually rare - but collectively common
Penetrance - High
Tests - Tests are predictive

Question 7

Describe complex gene disorders in terms of :

No of genes :
Pattern of inheritance: 
Rarity:
Tests:
Environmental influence:

Answer 7

No of genes - Risk alleles are at multiple genes (polygenic)
Pattern of inheritance - No simple pattern of inheritance, but runs in families
Rarity - Conditions are common
Tests - No reliable tests
Environmental influence - Influenced by the environment

Question 8

How many base pairs in the human genome?

Answer 8

3.2Gb (3x10^9) base pairs

Question 9

What percentage of the human genome is “coding”

Answer 9

1.1% (20,500 coding genes)

Question 10

What are coding and non coding regions of the genome called?

Answer 10

• Exons - coding

* Introns - non-coding

Question 11

What happens to the introns in pre-mRNA?

Answer 11

Introns removed in splicing

Question 12

What is ENCODE?

Answer 12

The Encyclopedia of DNA Elements (ENCODE) Consortium is an international research collaboration

Question 13

Describe whole genome sequencing? (3)

Answer 13

• Sequencing the entire genome
• Enormous amount of data
• More expensive

Question 14

What is whole exome sequencing?

Answer 14

• Targeted sequencing of only the protein encoding region of genome (1%)

Question 15

Where are mutations identified in single gene disorders?

Answer 15

Coding sequence

Question 16

Where are disease variants found in complex diseases?

Answer 16

Outside of the coding sequence

Question 17

What does NGS (next generation sequencing) enable

Answer 17

NGS enables the routine sequencing of whole genomes/exomes

(A human genome can be sequenced in 24 hours and costs in the region of $1000)

Technology - Illumina
Average Length of sequence read - 36
Average number of reads -35 000 000
Total amount of sequence - 1.3Gb
Cost/Mb - $6

Technology - Sanger
Average Length of sequence read - 800
Average number of reads - 384
Total amount of sequence - 300Kb
Cost/Mb - $600

Question 18

What is an example of :
Autosomal dominant disease
Autosomal recessive disease
X-chromosome linked disease

Answer 18

Huntington’s disease
Cystic fibrosis
Duschenes Muscular Dystrophy