10.1 Variation among genomes

Question 1

true or false and state why: A wild-type human genome sequence exists

Answer 1

false, the genome sequences of just 3 people reveal over 5 million DNA polymorphisms- sequence differences

Question 2

why is it that most polymorphisms do not influence phenotype?

Answer 2

This is because since codons make up less than 2% of the genome, many mutations in codons don’t change the amino acid. Many deletion mutations disappear from the population through natural selection.

Question 3

What are the four categories of genetic variation?

Answer 3

1. Single nucleotide polymorphisms (SNPs)- one base pair changes (1 bp and 1 per 1kb)
2. Deletion-insertion polymorphisms (DIPs)- short insertions or deletions of a single or a few base pairs ( 1-100 bp and 1 per 10kb)
3. Single sequence repeats (SSRs)- 1-10 base sequence repeats 15-100 times in tandem and 1 per 30kb
4. Copy number variants (CNVs)- large blocks of duplication or deletion with a population frequency of <1% (10bp-1 Mb and 1 per 30 Mb)

Question 4

What determines the origin of human SNPs?

Answer 4

the comparison to the other species.
For example, comparison of human and chimpanzee genomes reveals the SNPs that occurred since the divergence of these species

Question 5

Explain how unequal crossing over produces new alleles of copy number variants

Answer 5

CNVs are tandem sequence repeats more than 10bp long. Misalignment during meiosis leads to unequal crossing over. This is not a common event so most CNVs are inherited, rather than being a new mutation

Question 6

How many olfactory receptor genes do humans have at different loci (at each locus the number of genes differs)?

Answer 6

1000