Genome Ch. 21

What proportion of your genome consists of copies of transposable elements (or sequences derived from them)?

46% consist of copies of transposable elements Line Element -> A eukaryotic transposable element. -> Retrotransposon Codes for reverse transcriptase (enzyme that makes a DNA copy from mRNA transcript ) Also codes for Intergrase, which inserts LINE DNA Copy back into DNA at new location.

What are multigene families and how do they arise? Outline the steps involved. Give an example of a multigene family.

A multigene family is a member of a family of related proteins encoded by a set of similar genes. Multigene families are believed to have arisen by duplication and variation of a single ancestral gene. generates diversity for natural selection. example: genes coding for a- and b- globin subunits of human hemoglobin(blood carries oxygen to body)

Explain how "exon shuffling" can generate functional diversity in protein products.

Crossover events occurring within a genebetween exons, give rise to proteins withdifferent combinations of these domains."EXON SHUFFLING" ➔Introns provide room for crossovers to occur between exons, generating new varieties of potentially functional proteins.

Genes

DNA that specifies a product (Proteins or RNAs)

1. Using the chart in your text (Table 21.1) and shown in the lecture, compare the genomes of the bacterium E. coli, the single-celled yeast Saccharomyces cerevisiae, the nematode (roundworm) Caenorhabditis elegans, the flowering plant Arabidopsis thaliana and the human, Homo sapiens. Which has the largest genome? Which has the most genes? Which has the shortest genes (and why?)? Which has the greatest number of genes per length of DNA? As you compare increasingly complex organisms, do their genome size and their number of genes increase proportionately? Explain.

Humans have the largest genome size. next is the fruit fly. with bacteria being the smallest. Human has the most genes than the fruit fly. bacteria comes first with who has the longest genes, next the fruit fly, and lastly humans. This is because prokaryotes have smaller genes because they do not have introns stopping the translation.. think of it like watching a movie with a bunch of commercials. More complex organisms have larger genomes and more genes, but fewer genes length of DNA

How might expression of a gene be affected if a transposon becomes inserted within it, or within its promotor or other control element?

If a transposon inserts itself into a functional gene, it will probably damage it. Insertion into exons, introns, and even into DNA flanking the genes (which may contain promoters and enhancers) can destroy or alter the gene's activity. -> disrupt gene products or control elements -> carry genes or parts of gens to new location's, under different control. -> may ultimately generate variation significant in eukaryote evolution

In what ways does the composition of the eukaryote genome differ from that of prokaryotes?

In prokaryotes, most of the DNA codes for proteins (or rRNA or tRNAs). Noncoding portion mainly promoters and other regulatory sequences. Introns rare. In Eukaryotes, most of the DNA does NOT code for any functional product.

How might long introns within eukaryotic genes help explain the evolutionary success of the eukaryotes?

Introns, from this perspective, have a profound purpose. They serve as hot spots for recombination in the formation of new combinations of exons. In other words, they are in our genes because they have been used during evolution as a faster pathway to assemble new genes.

Describe stepwise how the retrotransposon LINE-1 spreads through the genome.

LINE- Long Interspersed Nuclear Elements (L1) 1. transposon transcribed 2. transposon translated 3. These enzymes make a DNA copy of the transcript and insert it into the genome LINE retrotransposons copy make up 17% of the human genome

Where in the genome are misaligned crossovers most likely to occur with the highest frequency, and why?

More frequent misaligned crossover's in meiosis and this is because of the homologous chromosomes.

What is a pseudogene?

Non-functional members of multigene family; mutations produced stop codons.

Approximately what proportion of the human genome represents coding sequences? Explain what the rest consists of.

Only 1.5% of the human genome representing coding regions /sequences. The rest consists of : 59% - Repetitive DNA (44% due to Transposable Elements & 15 due to unrelated Transopable Elements.) 24%-Introns and Regulatory Sequences 15% -Unique non-coding DNA

What are polyploid genomes? How might they come about? How are they significant in evolution of new species and groups? In what major group of organisms are they most common?

Polyploid genomes - some mutations result in duplication of entire sets of chromosomes . happens within nondisjuction (the homologous or sister chromatids didn't sperate) lethal in animals but many plants have the genomes. Ex: wheat.

In what ways might the presence of multiple copies of transposable elements contribute to genome evolution?

Presence of multiple transposon copies increases the frequency of misaligned crossovers during meiosis.

What are simple sequence repeats? In what parts of the chromosomes are they concentrated? Explain why individuals tend to differ in the number of copies they have of a given simple sequence.

Simple sequence DNA:: tandem repeats of non-coding DNA sequences. Most prevalent at centromeres and telomeres. EX: GACCGACCGACC Observed number of repeats for each of several short tandem repeat sequences will give a unique profile of a single individual.

What are transposable elements (transposons)? Explain what they do.

They are segment of DNA that move form one location to another within the genome, EX: homologous chromosomes exchange genetic information. * One type directs its own removal and reinsertion elsewhere. ("jumping genes"). -> Cut and Paste * Another type makes copies of itself and inserts the copies elsewhere in the genome. -> Copy and Paste (selfish DNA)

Explain how misaligned (unequal) crossing over occurs. What kinds chromosomal mutations are produced as a result?

Unequal crossing-over (UCO) occurs when distinct loci similar in sequence undergo homologous recombination during the pachytene stage of meiosis I and occasionally during mitosis. UCO usually occurs between misaligned chromatids on homologous chromosomes Misaligned crossing over results in gene DUPLICATIONS and DELETIONS

Multigene family

genes of common origin that arose by duplication

Regulatory Sequences:

non-coding DNA that acts as binding site for protein's that regulate gene transcription.