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40 Cards in this Set

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sister chromatids

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


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


Where microtubules attach to the chromosomes during mitosis.


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

mitotic spindle

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


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


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


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


threadlike structures made of DNA molecules that contain the genes

S Phase

When DNA replicates to form sister chromatids


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

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

1. Prophase

2. Prometaphase

3. Metaphase

4. Anaphase

5. Telophase

6. Cytokinesis


The first phase of mitosis where the chromosomes condense.


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.


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


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


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


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

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

S, G2, Beginning of M

When is DNA condensed in all or part of phase?

Beginning of M and End of M

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

S, G2, Beginning of M, End of M

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.

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.)

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

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

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.

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.)

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

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

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?

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.)

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?

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

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

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.)

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?

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

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?

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.)

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.

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.)

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?

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).)

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

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

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.

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

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

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.)

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?

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.)

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.)

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

Independent assortment explains _______.

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.)

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

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

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

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