Ch. 9.3

SNPs

Common variations between individuals at a certain nucleotide position in the genome are called:

Genes are more sparsely distributed in humans than in yeast or flies.

Comparing the DNA of different organisms reveals interesting insights into how our genomes are arranged. Shown in the figure are random segments of DNA-each about 50,000 nucleotide pairs in lenght-from yeast, Drosophilia, and human. Exons are shown in orange, introns in yellow, and repetitive sequences in blue. What can be concluded based on this comparison?

They are essentially the same in humans, chimps, and mice

Which of the following is NOT true about noncoding DNA sequences?

Almost half the human genome consists of mobile genetic elements

Which of the following is true about the human genome?

True

T or F: Copy-number variations can contain genes.

30,000

Approximately how many genes are in the human genome?

1.5%

Approximately what percentage of the human genome codes for proteins?

The Neanderthal sample does not appear to have been contaminated by human DNA and thus represents a valid Neanderthal sequence

Comparison of human Neanderthal DNA sequences can reveal the genetic changes that helped to make us human. Such comparisons, however, are made more difficult by the possibility of contamination: should any human cells get mixed in with the Neanderthal samples, modern human traits may be hailed as ancient and the real differences between the sequences would be missed. One way to check for contamination is to make a pairwise comparison among all of the human DNA samples. This comparison will yield an estimate of the amount of variation that is naturally present in a representative human population. These human sequences can then be compared with the sequence of the Neanderthal sample to see if the amount of variation differs. Shown in the figure is the result of such a comparison. Nearly 1,000 samples of human DNA were compared to one another and to a single sample of Neanderthal DNA. In both cases, investigators looked at mitochondrial DNA, which is often used to chronicle the evolution of species that diverges very recently. For added reference, the human mitochondrial DNA samples were also compared with about a dozen sequences from the mitochondria of chimps. What conclusion can be drawn from these results?

Population B most likely enjoys a diet higher in starch

Copy-number variations can sometimes include entire genes, so that the affected individuals possess more than the traditional two copies of any gene. For example, in some populations, individuals have up to nine copies of the gene that encodes salivary amylase, an enzyme that breaks down starch. In this case, the more copies of the amylase gene the individuals have, the more enzyme they produce. The graph shows how many copies of the amylase gene (AMY1) are present in the genomes of individuals from two different populations. Based on these data, what can be concluded about these populations?

An average of 1 nucleotide in 1,000

Humans differ from one another by how much?

A calculation based on the size of the genome and the average size of the genes that had been sequenced.

In the mid-1980s, Walter Gilbert, a physicist-turned-biologist, suggested that humans could have 100,000 genes. On what did he base this ballpark estimate?

Single-nucleotide polymorphisms

Most of the genetic variation in the human genome takes what form?

Presence of mobile genetic elements

One way to identify protein-coding genes is to search a DNA sequence for open reading frames-long sequences of 100 or more codons that lack a stop codon. But this process can be made more difficult by the fact that in higher eukaryotes, genes can stretch over tens of thousands of nucleotide pairs, much of which contains introns. To help find the exons buried within this noise, computers can be used to search for other distinctive features that mark the presence of a protein-coding gene. Which is NOT considered a feature characteristic of a protein-coding gene?

True

T or F: An organism can produce far more distinct proteins than would be expected based on its number of genes.

True

T or F: Most of the genetic variation in the modern human genome was most likely already present in our early human ancestors.

True

T or F: The evolution of species is likely to have more to do with innovations in gene regulatory sequences than in the proteins or functional RNAs those genes encode.

False (It contains 3.2 x 10^9)

T or F: The human genome contains 3.2 x 10^6 nucleotide pairs divided among 22 autosomes and 2 sex chromosomes

True

T or F: Two people selected at random from anywhere on Earth are likely to be identical with respect to 99.9% of their nucleotides.

a chimp.

To determine what makes humans the unique animal that we are, it is most useful to compare our genome with that of: