W3: Genetic Variation & Chromosomal basis for inheritance

Question 1

What proportion of DNA codes for proteins?

Answer 1

~1.5%

Question 2

What is the typical difference between the genomes of two individuals?

Answer 2

~0.1%
(~3mil SNPs out of the 3.2bil bp)

Question 3

Why is the proteome larger than the genome?

Answer 3

Alternative splicing

Question 4

Types of mutations

Answer 4

Hereditary:
* present in virtually every cell; can be passed to offspring

Somatic:
* Acquired at some point at time; present in certain cells (early mutation = larger proportion of mutant cells)
* cannot be passed down to next gen.
* e.g. cancer cells

Question 5

Example condition of microsatellite instability (tandem repeats)

Answer 5

Huntington’s disease
- Repeat of CAG codon produces poly-glutamine
- This induces aggregation of protein –> Progressive disease
- Neurological symptoms

Note: High repeat count causes earlier onset & increases risk to offspring

Question 6

Advantage (e.g.) of Copy Number Variations

Answer 6

AMY1
- high AMY1 is favourable –> more efficient starch digestion

Question 7

What type of genetic disorder is sickle cell anaemia?

Answer 7

autosomal recessive

Question 8

Differences between meiosis of the 2 sexes

Answer 8

• Males (spermatogenesis):
  
  • Symmetrical – all 4 sperm have 23 chromosomes (haploid)
  • Creates 4 functional sperm
• Females
  
  • Asymmetrical – creates 1 oocyte (large cell) and discards the polar body cells
  • Creates only 1 functional egg

Question 9

Q: If mammalian women have two X-chromosomes and men only one, will women have twice as many gene products as men from their X-chromosome?

Answer 9

A. This doesn’t happen, because in mammals one of the X-chromosomes gets switched off (heterochromatin silences one X-chromosome)

note: exceptions do exist e.g. tortoiseshell cats are only female, requires two X chromosomes

Question 10

What is the principle of linked genes (linkage)

Answer 10

Genes that are close together on the same chromosome tend to be inherited together

Question 11

What is the limitation of Mendelian’s Law of Independent Assortment?

Answer 11

Linked genes

Question 12

What is aneuploidy? (+example conditions)

Answer 12

• presence of an abnormal no. chromosomes in a cell
• e.g. down syndrome - autosomal chromosomes —> trisomy 21
• e.g. turner syndrome - sex chromosomes —> absence of 1 X chromosome in females