BSC2010 Unit 3 Lecture 6

What is the main reason genome size varies greatly between species?

Differences in amount of non-coding DNA

What percent of human DNA is protein-coding?

3%

Genomes are measured in ___.

base pairs

Interpret this graph

Smaller organisms tend to have higher percent of coding DNA, but there are exceptions.

Pseudogene

Noncoding DNA that lost its original function

Functions of noncoding DNA

-Alter expression of surrounding genes

-Occasionally develop novel functions

-Help maintain chromosome structure

-Transposons (jumping genes)

The amount of noncoding DNA may be related to ____.

population size

“Two-fold cost of sex”

-A female only passes 50% of her genes to each offspring (cost of meiosis)

-Dividing offspring into genders reduces a female’s overall reproductive rate (cost of males)

Another disadvantage of sexual reproduction

Recombination can break up adaptive combinations of genes

In a sexually-reproducing population, what do we expect of a single asexual mutant?

Higher fitness → quickly spread

Advantages of sexual reproduction

-Elimination of deleterious mutations through recombination

-Variety of genetic combinations in each generation can be advantageous

-Facilitates repair of damaged DNA

Muller’s ratchet

In a non-recombining genome, deleterious mutations accumulate (“ratchet up”) in each successive generation.

How are deleterious mutations eliminated in asexual species?

Death of the lineage

Does sex directly influence the frequencies of alleles?

No, it generates new combinations of alleles on which natural selection can act.

Lateral gene transfer

Individual genes, organelles, or genome fragments move horizontally from one lineage to another.

Examples of lateral gene transfer

Antibiotic resistance. wolbachia in insects

Different fates of gene copies

1. Both copies retain original function

2. Each copy may specialize

3. One copy accumulates deleterious mutations and becomes a functionless pseudogene

4. One copy retains original function and the other evolves a new function.