Darwin stressed that species evolve by natural selection. What was the main gap in his theory?

All of the statements are correct regarding ecological succession EXCEPT

Select one:

a. there is less competition earlier in the succession process

b. it is a random process

c. initial pioneer species are plants

d. species diversity increases as succession proceeds

Which situation is an example of a prezygotic barrier?

a. Two species of fish produce sterile offspring.

b. Two species of flowers attract different pollinators.

c. Two species of insects mate, but the zygote does not survive.

d. Two species of lizards mate, but the offspring dies before reproducing

Which reproductive combination produces hybrids? a. when individuals of the same species in different geographical areas reproduce, b. when any two individuals sharing the same habitat reproduce, c. when members of closely related species reproduce, d. when offspring of the same parents reproduce.

Dispersed, repetitive sequences such as transposable elements may have played a role in duplicating short regions in a genome. Can you suggest a mechanism?

A geneticist has studied the sequence of a gene in each of three species, A, B, and C. Species A and species B are sister species; species C is more distantly related. The geneticist has calculated the ratio of nonsynonymous (NS) to synonymous (S) nucleotide substitutions in the coding region of the gene in two ways—first, by comparing the gene sequences of species A and C, and second, by comparing the gene sequences of species B and C. The NS:S ratio for the comparison of species B and C is five times greater than it is for the comparison of species A and C. What might this difference in the NS:S ratios suggest?

How might you explain the thousandfold difference in the evolutionary rates of fibrinopeptide and histone $3$?

The coding sequence of the alcohol dehydrogenase (Adh) gene of Drosophila melanogaster consists of $765$ nucleotides ($255$ codons); $192$ of these nucleotides are functionally silent—that is, they can be changed without changing an amino acid in the Adh polypeptide. In a study of genetic variation in the Adh gene, Martin Kreitman observed that $13$ of the $192$ silent nucleotides were polymorphic. If the same level of polymorphisms existed among the nonsilent nucleotides of the Adh gene, how many amino acid polymorphisms would Kreitman have observed in the populations he studied?

If the evolutionary rate of amino acid substitution in a protein is K, what is the average length of time between successive amino acid substitutions in this protein?

What is a characteristic feature that is absent in prokaryotes?

A viral disease that destroys the cells of the anterior gray horn will ______________.

If a randomly mating population is segregating n selectively neutral alleles of a gene and each allele has the same frequency, what is the frequency of all the homozygotes in the population?

Ribonuclease, a protein that degrades RNA, is $124$ amino acids long. A comparison between the amino acid sequences of cow and rat ribonucleases reveals $40$ differences. What is the average number of amino acid substitutions that have occurred per site in these two evolutionary lineages? If the cow and the rat lineages diverged from a common ancestor $80$ million years ago, what is the rate of ribonuclease evolution?

During the early evolutionary history of the vertebrates, a primordial globin gene was duplicated to form the $\alpha$- and $\beta$-globin genes. The rate of evolution of the polypeptides encoded by these duplicate genes has been estimated to be about $0.9$ amino acid substitutions per site every billion years. By comparing the human $\alpha$- and $\beta$-globins, the average number of amino acid substitutions per site has been estimated to be $0.800$. From this estimate, calculate when the duplication event that produced the $\alpha$- and $\beta$-globin genes must have occurred.