End-of-topic test: Mutations and Genetic Variation

A strand is written from its 5′ end to its 3′ end, and both ends are marked. The DNA shown is the coding strand, so its letters match the mRNA’s, with T where the mRNA has U. The original is drawn above the changed copy, both grouped in threes from the start codon. Suppose a scorpionfly’s gene for a leg-joint protein changes. The original coding strand and the changed copy are drawn below.

Which kind of change is drawn?

The DNA shown is the coding strand, so its letters match the mRNA’s, with T where the mRNA has U. The original codon is drawn above the changed codon. Suppose one codon on the coding strand of a gerenuk’s gene for a muscle protein has changed from 5′-ATT-3′ to 5′-GTT-3′, drawn above the chart. Gerenuks are long-necked antelopes.

Which kind of mutation is this?

The DNA shown is the coding strand, so its letters match the mRNA’s, with T where the mRNA has U. Suppose one codon on the coding strand of a bristletail’s gene for a protein in its legs changes from 5′-GAA-3′ to 5′-TAA-3′. The changed codon is the 60th of about 320. On the mRNA, GAA names Glu, and UAA is a stop codon.

Which of the following describes the protein made from the changed gene?

Suppose a biologist compares the gene for a cartilage protein in two gorals, a kind of goat-antelope. The second goral’s copy carries one changed base. Both copies give an mRNA 1,380 nucleotides long, and both proteins have the same 460 amino acids in the same order. The table gives the mean mRNA per cell for each copy, with its standard error (SE).

Where did the changed base land?

Suppose two related bacteriophages infect one bacterium. Each bacteriophage carries one molecule of DNA. Inside the cell both molecules are copied, and every base is paired correctly. A new bacteriophage leaves the cell carrying a DNA molecule whose first half matches the first bacteriophage’s DNA and whose second half matches the second’s.

Which event made the new bacteriophage’s DNA?

Suppose a steenbok, a small antelope, carries a mutation that doubles the size of its ears. Blood flowing through the large ears sheds body heat quickly in hot air and loses body heat quickly in cold air.

In which of the following places does the mutation raise the steenbok’s chance of surviving and reproducing?

In a booklouse, a tiny insect, one stretch of DNA at one place on a chromosome carries the instructions for a protein of its jaws. In some booklice one base of that stretch is a G. In others that base is a T, and every other base is the same. A booklouse is diploid: it carries one copy of that chromosome from each parent.

How many different alleles of the jaw-protein gene can one booklouse carry at most?

A population of snakeflies carries three alleles of a gene for a protein of its wing veins. Over one generation, crossing over, independent orientation and fertilization shuffle the alleles, and no base of the gene changes in any cell.

Which of the following is the largest number of alleles of that gene the next generation can carry?

A biologist grows cells from a lechwe, an antelope, for 50 divisions in three dishes and then counts the new mutations in each cell’s DNA. The table gives the mean count per cell for each dish.

Which of the following is the source of the 35 new mutations in the cells grown in plain medium?

Suppose an animal’s cell copies 4,800,000,000 base pairs each time it copies its DNA, and about one uncorrected error stays in every 400,000,000 base pairs copied.

How many uncorrected errors does one copying of the cell’s DNA leave?

Suppose one species of bacterium lives in the water of a flower vase, and none of its cells carries a gene for an enzyme that digests plant fibers. A cell of a second species arrives on a cut stem carrying a plasmid with such a gene. Over a week, the two species form bridges, and plasmid copies cross into many cells of the first species. No cell of the first species mutates in that gene.

Which of the following describes the first species after the week?

A technician spreads a bacterium over two plates of plain jelly. Seventy colonies grow on one, sixty-five on the other. She stamps each plate’s colonies onto two plates whose jelly holds a mouthwash that kills most bacteria, then onto one more plain plate. In every plate drawing, a dot is one colony, the large plate at the top is the first plate, and the small plates beneath it are the plates the stamp was pressed onto, in a row.

Which of the following explains why the colonies on the two pairs of mouthwash plates sit at different positions?

The drawing below sorts the chromosomes of an animal’s zygote into kinds by length: a karyotype. A dark rod came from the mother, and a light rod came from the father.

Which of the following does the karyotype show?

Suppose a plant’s zygote holds 5 complete sets of chromosomes: 5 copies of every gene.

Which of the following is the relative amount of any gene’s product in the zygote’s cells, as a multiple of the usual amount?

In the drawing, each box is one segment of a chromosome, and each segment carries many genes. The chromosome before the change is drawn above, and after it beneath. A second chromosome, where drawn, sits beneath the first with its own letters. A change in the structure of the chromosomes in a cell is drawn below.

Which kind of change is this?

Suppose a nyala’s egg carries a chromosome on which one segment, about 60 genes long, appears twice. A normal sperm fertilizes the egg. Every gene on the segment keeps its sequence.

Which of the following describes the amount of each of those 60 genes’ proteins in the zygote’s cells?

In a drop of water from a watering can, a cell of one bacterial species bursts, and its DNA spills into the water in pieces. The drop holds no bacteriophage, and no cell in it forms a bridge to another. An hour later a cell of a second species carries, joined into its chromosome, a gene the burst cell had.

Which route brought the gene into the second species’ cell?

In a bacterium living on the surface of a leaf, a stretch of DNA in the chromosome cuts itself out and joins in again in the middle of the gene for a protein of the cell’s flagellum, the whip-like tail the cell swims with.

Which of the following describes the flagellum gene now?

Crossing over happens in the meiosis of a yeast cell, a fern, a lanternfly and a human, and in each of them it happens the same way.

Which of the following explains why the four share crossing over?