ANSC 221: Lecture G16 - Genomes and their Evolution

What is the composition of the genome of eukaryotes?

The genome consists of coding (genes) and noncoding nucleic acid sequences.

Do humans and other mammals have the highest gene density?

False, they have the lowest gene density.

What percentage of the human genome does not code for proteins, rRNAs, or tRNAs?

98.5%.

What accounts for 5% of the human genome?

Gene regulatory sequences.

What are pseudogenes?

Genes that have accumulated mutations and are nonfunctional.

What mechanism do transposons use to move within a genome?

They use a DNA intermediate and require a transposase enzyme.

What is the difference between 'cut-and-paste' and 'copy-and-paste' transposons?

'Cut-and-paste' removes the element from the original site, while 'copy-and-paste' leaves a copy behind.

What are Alu elements?

They make up 10% of the human genome and may regulate gene expression.

What percentage of the human genome is made up of LINE-1 (L1) elements?

17%.

What are some causes of other repetitive DNA in the human genome?

Mistakes during DNA replication or recombination.

What are multigene families?

Groups of identical or very similar genes.

What role do mutations play in genome evolution?

They are the basis of change at the genomic level.

How many pairs of chromosomes do humans have?

23 pairs.

How do humans and chimpanzees differ in chromosome count?

Humans have 23 pairs, while chimpanzees have 24 pairs.

How can one copy of a duplicated gene evolve novel functions?

It can undergo alterations leading to a completely new function for the protein product.

How do transposable elements contribute to genome evolution?

They facilitate recombination between different chromosomes and may create new sites for alternative splicing.

What insights can comparing genome sequences provide?

They reveal insights into evolutionary history and recent evolutionary events.

What is the difference in genome sequences between humans and chimpanzees?

They differ by 1.2% at single base pairs and by 2.7% due to insertions and deletions.

What types of genes are evolving faster in humans?

Genes involved in defense against diseases and the regulation of brain size.

What is the definition of a genome?

A genome consists of coding and noncoding sequences.

How do prokaryotic genomes compare to eukaryotic genomes?

Prokaryotes have small genomes (1-6 Mb), high gene density, few introns, and little noncoding DNA, while eukaryotes have larger genomes (10-4,000 Mb+), lower gene density, many introns, and lots of noncoding DNA.

What is the approximate size of the human genome?

About 3,000 Mb with approximately 21,300 genes.

What percentage of the human genome is noncoding DNA?

98.5% does not code for proteins, rRNA, or tRNA.

What are the key elements of noncoding DNA in humans?

Regulatory sequences (~5%), introns (~20%), repetitive DNA (~44%).

What are Alu elements and LINE-1 (L1) in the human genome?

Alu elements (~10%) and LINE-1 (L1) (~17%) are types of repetitive DNA that play roles in gene regulation and chromatin structure.

What are transposable elements?

DNA stretches that move within the genome, including transposons and retrotransposons.

What is the difference between transposons and retrotransposons?

Transposons use a DNA intermediate and a transposase enzyme, while retrotransposons use an RNA intermediate and reverse transcriptase.

Who provided the first evidence of transposable elements?

Barbara McClintock through her maize experiments.

What is the significance of gene duplication?

Gene duplication allows one copy to evolve new functions, contributing to genetic diversity.

What is exon shuffling?

Errors in meiosis or recombination that mix exons to create new genes.

How do transposable elements facilitate evolution?

They facilitate recombination, alter protein production, and create new sites for alternative splicing.

What is comparative genomics?

The comparison of genome sequences to reveal evolutionary history.

How do human and chimpanzee genomes compare?

They differ by 1.2% in single base pairs and 2.7% in indels.

What are the main takeaways regarding genome size and organism complexity?

Genome size does not equal organism complexity; humans have low gene density despite large genomes.

What role do chromosomal rearrangements play in evolution?

Chromosomal rearrangements can lead to speciation events and highlight evolutionary divergence.

What is the impact of mutations on genomic change?

Mutations are the basis of genomic change and contribute to evolutionary diversity.

What is the significance of large-segment duplications in the genome?

They contribute to genomic diversity and can lead to new gene functions.

What is the role of pseudogenes in the genome?

Pseudogenes are nonfunctional, mutated genes that provide insights into evolutionary history.

What is the effect of unequal crossing over in genetics?

It can lead to deletions and duplications, impacting gene function and evolution.