Bio 340 - Mg Exam 1

Front 1

sister chromatids

Back 1

Two identical DNA molecules, produced during DNA replication that separate during mitosis.

Front 2

Centromeres

Back 2

The region where the identical DNA molecules are most tightly attached to each other, after chromosomes condense.

Front 3

kinetochores

Back 3

Where microtubules attach to the chromosomes during mitosis.

Front 4

interphase

Back 4

Where most of the cell growth occurs, in dividing cells.

Front 5

mitotic spindle

Back 5

A structure consisting of microtubules, which forms during early mitosis and plays a role in cell division.

Front 6

chromatin

Back 6

A complex of DNA and protein in a dispersed form filling most of the nucleus, during interphase.

Front 7

cytokinesis

Back 7

When the rest of the cells divides, following division of the nucleus in most eukaryotes.

Front 8

centrosomes

Back 8

The organizing centers for microtubules involved in separating chromosomes during mitosis.

Front 9

chromosomes

Back 9

threadlike structures made of DNA molecules that contain the genes

Front 10

S Phase

Back 10

When DNA replicates to form sister chromatids

Front 11

Prophase

Back 11

When chromosomes condense, they then stay condensed until the forming of the two daughter cells.

Front 12

The order of the 5 stages of mitosis and the splitting of the cytoplasm into daughter cells

Back 12

1. Prophase

2. Prometaphase

3. Metaphase

4. Anaphase

5. Telophase

6. Cytokinesis

Front 13

Prophase

Back 13

The first phase of mitosis where the chromosomes condense.

Front 14

Prometaphase

Back 14

The second subphase of mitosis, in which discrete chromosomes consisting of identical sister chromatids appear, the nuclear envelope fragments, and the spindle microtubules attach to the kinetochores of the chromosomes.

Front 15

Metaphase

Back 15

the second phase of mitosis where the chromosomes line up across the center of the cell. Each chromosome is connected to a spindle fiber at its centromere

Front 16

Anaphase

Back 16

The third phase of mitosis, during which the chromosome pairs separate and move toward opposite poles

Front 17

Telophase

Back 17

The final stage of mitosis or meiosis, during which a nuclear membrane forms around each set of new chromosomes.

Front 18

Cytokinesis

Back 18

The final stage of the cell cycle, in which the cell's cytoplasm divides, distributing the organelles into each of the two new cells.

Front 19

When are sister chromatids present in all of part of the phases?

Back 19

S, G2, Beginning of M

Front 20

When is DNA condensed in all or part of phase?

Back 20

Beginning of M and End of M

Front 21

When is DNA content per cell doubled in all or part of phase?

Back 21

S, G2, Beginning of M, End of M

Front 22

Which of the following would be true of a plant heterozygous for a single gene controlling flower color? (Assume complete dominance).

A. It displays the recessive flower color.

B. About half of all its progeny will display the recessive flower color.

C. If crossed with another heterozygous plant, the majority of progeny will have the dominant flower color.

D. It will produce gametes with recessive flower color alleles and gametes with dominant flower color alleles in about a 3:1 ratio.

Back 22

C. If crossed with another heterozygous plant, the majority of progeny will have the dominant flower color. (There will be roughly three times as many plants with the dominant flower color as plants with the recessive flower color.)

Front 23

The 3:1 phenotypic ratio observed among progeny of an F1 X F1 cross requires random union of gametes.

Back 23

True. (The 1:2:1 genotypic ratio represents relative probabilities of gamete combinations based on the assumption that gamete union is random.)

Front 24

Of the methods listed below, which would be the best way to determine which of two alleles of a gene is dominant to the other?

A. Observe the relevant phenotype among the progeny of several crosses between individuals within a single, pure-breeding line.

B. Count the number of recessive individuals resulting from a cross between two recessive parents.

C. Perform crosses between series of randomly selected pairs to see which phenotype occurs more frequently.

D. Observe the relevant phenotype in the progeny that result from a cross between individuals from two different pure-breeding lines.

Back 24

D. Observe the relevant phenotype in the progeny that result from a cross between individuals from two different pure-breeding lines. (All progeny will be heterozygous for the trait in question and will display the phenotype that corresponds with the dominant allele.)

Front 25

In an individual that is heterozygous for a particular trait, the recessive allele is not expressed.

Back 25

True. (Only the dominant allele is expressed in an individual that is heterozygous for a particular trait.)

Front 26

Round (R) seed shape is dominant to wrinkled (r) seed shape in pea plants. If an RR plant is crossed with an rr plant, what is the frequency of phenotypes in the F2 generation?

Back 26

3 round seeds, 1 wrinkled seed. (The F1 generation would have the genotype Rr, so crossing two heterozygotes would result in 3 plants with round seeds and 1 plant with wrinkled seeds.)

Front 27

If the first three F2 offspring grown from the cross described above are round, what is the probability that the next F2 offspring will be wrinkled?

Back 27

25%. (The proportion of rr is ¼, so the next offspring has a 25% chance of being wrinkled.)

Front 28

The law of independent assortment states that one gene in a pair is always dominant to the other.

Back 28

False. (The law of independent assortment states that during gamete formation, segregating pairs of unit factors assort independently of each other; the law says nothing about dominance.)

Front 29

If a yellow pea plant with round seeds that has the genotype GgWw is crossed to itself, what proportion of the offspring will be green with round seeds?

Back 29

3/16. (This is the probability of offspring that are either green with round seeds or yellow with wrinkled seeds.)

Front 30

The following phenotypic ratios are determined for a trihybrid cross in which the gametes assort independently: A 1 : A 2 = ¼ : ¾ B 1 : B 2 = ¼ : ¾ C 1 : C 2 = ¾ : ¼ What is the probability that the F2 offspring will have the phenotype A 1 B 1 C 1?

Back 30

3/64. (This is the probability that the offspring will be A 1 B 1 C 1, A 1 B 2 C 2, or A 2 B 1 C 2.)

Front 31

Which of the following phenomena is a consequence of Independent Assortment?

A. The phenotypic ratio among phenotypes produced from an F1 X F1 dihybrid cross is 9:3:3:1.

B. For any gene displaying complete dominance, heterozygous individuals exhibit the dominant phenotype.

C. Smooth seed trait is dominant to wrinkled seed trait in peas.

D. Pure breeding plants, when mated with each other, produce completely homozygous offspring.

Back 31

A. The phenotypic ratio among phenotypes produced from an F1 X F1 dihybrid cross is 9:3:3:1. (The 9:3:3:1 ratio requires that the four gamete classes produced occur with equal frequency. This requires independent assortment.)

Front 32

A pea plant is heterozygous for two genes; one controlling height, one controlling color. The genotype is written PpTt. Based on the Law of Independent Assortment, approximately what proportion of the pollen produced by this plant should have the genotype PT?

Back 32

1/4. (There are four different possible genotypes. Independent Assortment assumes that all are equally likely. Therefore, each of the four should occur with roughly equal frequency (1/4).)

Front 33

The 9:3:3:1 ratio exhibited in the F2 generation of a dihybrid cross is a genotypic ratio.

Back 33

False. (There are more than four different genotypes in the F2 generation of a dihybrid cross.)

Front 34

Which of the following statements is true regarding a trihybrid cross between two true-breeding homozygous individuals with contrasting phenotypes?

A. The F2 generation has 4 different phenotypes.

B. The least frequent F2 phenotypic class is recessive for all three traits.

C. The laws of probability cannot be used in crosses with three or more traits.

D. The most frequent F2 phenotypic class is recessive for all three traits.

Back 34

B. The least frequent F2 phenotypic class is recessive for all three traits. (1/64 of the F2 phenotypes is triply recessive.)

Front 35

How could the botanist best determine whether the genotype of the green-pod plant is homozygous or heterozygous?

Back 35

cross the green-pod plant with a yellow-pod plant. (A cross between a plant of unknown genotype and one that is known to be homozygous recessive is called a test cross because the recessive homozygotetests whether there are any recessive alleles in the unknown. Because the recessive homozygote will contribute an allele for the recessive characteristic to each offspring, the second allele (from the unknown genotype) will determine the offspring’s phenotype.)

Front 36

Suppose that the botanist carried out the test cross described in Parts A and B and determined that the original green-pod plant was heterozygous (Gg). Which of Mendel’s findings does her test cross illustrate?

Back 36

law of segregation. (The law of segregation states that the two alleles for a gene separate during gamete formation, and end up in different gametes. In the case of the heterozygous green-pod plant (Gg), one gamete will receive the dominant allele (G), and the other gamete will receive the recessive allele (g). The law of segregation accounts for the prediction that 50% of the offspring of the test cross will have green pods and 50% will have yellow pods.)

Front 37

During which part of meiosis (meiosis I or meiosis II) do the two alleles of a gene separate? During which phase does the separation occur? (Assume no recombination.)

Back 37

meiosis I, anaphase. (Alleles separate from one another during anaphase of meiosis I, when the homologous pairs of chromosomes separate.)

Front 38

Independent assortment explains _______.

Back 38

why a collection of meiotic products that includes gametes of genotype Ab will also include gametes of genotype AB in roughly the same proportion. (Because alignment of the chromosomes is random, the alignment that produces Ab is just as likely as the alignment that produces AB. Therefore, the two genotypes should both occur with equal frequency.)

Front 39

Independent assortment occurs only in cells that are heterozygous for two genes (AaBb) and not in cells that are completely homozygous (AABB or aabb).

Back 39

false. (Even though there would be no genotypic differences in the products of such meioses, random alignment of chromosomes would still have occurred.)

Front 40

Which of the following genotypes represents a gamete produced by a failure to segregate during meiosis in a cell of genotype AaBbCC?

Back 40

AaBC. (This gamete contains two copies of gene "A". Proper segregation would have separated A from a and allowed only one copy per gamete.)