OEB Exam 3 - Human Genome / Evo Devo

What is the C-Value paradox?

There is no clear correlation between genome size and level of complexity

Why are smaller genomes more streamlined?

The metabolic cost of extra DNA is very high in smaller genomes because they are under strong selection for rapid generation times which prevents having too much DNA

What is the correlation between population size and genome size?

Species with smaller population sizes tend to have larger genome sizes because they tend to accumulate repetitive DNA and genomic duplications. In small population sizes, the stochastic effects of genetic drift can swamp the deterministic effects of natural selection

Difference between larger population sizes and smaller? (correlation b/t genome size and population size)

In species with larger population sizes, selection is more effective at eliminating slightly deleterious extra DNA. In smaller population sizes, drift overcomes selection, resulting in the accumulation of extra DNA

How much of the human genome encodes proteins?

1.5%

What percentage of the human genome is under purifying selection?

11% - this selection conserves coding regions/functional proteins, regulatory DNA, and RNA genes. Mutations in these regions will lower organisms fitness

What is purifying selection?

A process in natural selection where deleterious mutations are removed in order to preserve beneficial traits

What contributes to genome activity?

Transposable elements act like parasites, creating copies of themselves that are distributed throughout the genome. (Genomes develop the ability to suppress this transposable activity)

Why is redundancy critical when it comes to adding new genes?

Redundancy is critical because it allows one copy of the gene to evolve while the other one performs its original function

Polyploidization

The process by which an organism ends up with more than one set of chromosomes

How does polyploidization relate to genome duplication?

Whole genome duplication can occur through genome duplication. This is common in plants as they can propagate infertile intermediate forms through vegetative reproduction

Why is the ease of fixation of novel chromosomal rearrangements so puzzling

Because meiosis in heterokaryotypes causes so many problems (low fertility, bad gametes), we expect natural selection to act against novelWha rearrangements

What the explanation for the ease of this fixation?

Selective disadvantage can be overcome by drift in smaller population sizes

How is gene duplication mediated?

By unequal crossing over that results in extra copies of a gene in one gamete and missing copies in another

Paralogs

Different genes in same organism: Genes within a single species that arose from a gene duplication event and may evolve to have new redundant functions

Orthologs

Same gene in different organisms: Genes in different species that are related by a speciation event

Pseudogenes

Defunct copy of a gene that resembles a functional gene and have accumulated mutations rhat prevent it from being transcribed/translated into functional gene

Subfunctionalization

When both copies diverge in function to produce a different but related protein

Neofunctionalization

When only one copy acquires a new function

Pseudogenization

When copy develops a mutation that renders it inactive/incomplete

Peto’s Paradox

The observation that larger animals like whales and elephants do not experience higher levels of cancer than small animals, despite having many more cells => more p53, redundancy is key because if one copy is affected by mutation others can perform required function

What is once case of family gene duplication?

Globins, which have acquired many multiple life stage-appropriate forms

What’s an important source for novel genetic information?

HGT is an important source for novel genetic material, especially in microbes, since they habitually incorporate environmental DNA

De novo genes

Genes that have arise from previously non-coding material

What’s the most common way new genes arise in eukaryotes?

Gene duplication