Question 1

The diploid number of a roundworm species is 4. Assuming there is no crossover, and random segregation of homologs during meiosis, how many different possible combinations of chromosomes might there be in the offspring?

Accepted Answer

The number of different possible combinations of chromosomes that might occur in the offspring can be calculated using the formula 2n, where n is the number of homologous pairs of chromosomes. In this case, the diploid number is 4, which means that there are two homologous pairs of chromosomes. Using the formula, we get 2^2 = 4. Therefore, each gamete can have one of four possible combinations of chromosomes (i.e. AB, Ab, aB, ab). When these gametes combine during fertilization, the total number of possible combinations of chromosomes in the offspring is 4 x 4 = 16. Therefore, the best choice is C) 16.

Question 2

Which of the following would enable you to detect aneuploidy?

Accepted Answer

Aneuploidy refers to the abnormal number of chromosomes in a cell, which can be detected by analyzing the chromosomes' karyotype, typically by examining the number and structure of chromosomes in a sample of cells. Thus, karyotyping is the best choice for detecting aneuploidy among the given options. Autosomy refers to the inheritance of traits on autosomes, which is not directly related to aneuploidy detection. Syngamy and synapsis are biological processes involved in sexual reproduction and chromosome pairing, respectively, which are not specific to detecting aneuploidy.

Question 3

Homologous chromosomes ________.

Accepted Answer

Homologous chromosomes are pairs of chromosomes that contain the same genes, but may have different alleles for those genes. They are similar but not identical, and carry information for the same traits. Option A is incorrect because homologous chromosomes are not identical, but rather similar. Option C is incorrect because homologous chromosomes may have different alleles for the same genes. Option D is incorrect because homologous chromosomes align on the metaphase plate in meiosis I, not meiosis II.

Question 4

Hexaploid wheat was produced synthetically by He and co-workers. They mated the diploid species, A. tauschii, and the tetraploid species, T. turgidum. Which of the following is an accurate statement about the relative contribution of each parent to the genome of the hexaploid offspring?

Accepted Answer

Aegilops tauschii contributed two sets of chromosomes (2n) and T. turgidum contributed four sets of chromosomes (4n), resulting in a total of six sets of chromosomes (6n) in the hexaploid offspring.

Question 5

For the duration of meiosis I, each chromosome ________.

Accepted Answer

The answer of For the duration of meiosis I, each...

Question 6

What makes sexually reproduced offspring genetically different from their parents?

Accepted Answer

During meiosis, genetic recombination occurs through crossing over which creates new combinations of genes in the offspring. This is why sexually reproduced offspring are genetically different from their parents.

Question 7

In the snail Pomacea patula catemacensis, n = 13. What is the diploid number for this organism?

Accepted Answer

The diploid number is twice the haploid number, so the diploid number for this organism would be 2 x 13 = 26.

Question 8

The egg of a fruit fly has 4 individual chromosomes. How many chromosomes are in a somatic cell of a fruit fly?

Accepted Answer

Somatic cells are diploid and have two sets of chromosomes. Fruit flies have eight chromosomes in each somatic cell, with four homologous pairs. Therefore, the correct answer is C, which represents 8 chromosomes.

Question 9

Homologous pairs of chromosomes align opposite to each other at the equator of a cell during ________.

Accepted Answer

Homologous pairs of chromosomes align opposite to each other at the equator of a cell during metaphase I of meiosis. In metaphase I, homologous chromosomes form a line known as the metaphase plate or equator of the cell. This is where the pair of homologous chromosomes align opposite to each other.

Question 10

Crossing over normally takes place during which of the following processes?

Accepted Answer

Crossing over, the exchange of genetic material between homologous chromosomes, occurs during prophase I of meiosis I. This process does not occur during mitosis or meiosis II.

Question 11

Quaking aspen can send out underground stems for asexual reproduction. Sexual reproduction is not as common, but when it does happen, the haploid gametes have 19 chromosomes. How many chromosomes are in the cells of the underground stems?

Accepted Answer

The haploid gametes have 19 chromosomes which means the diploid sporophyte must have 38 chromosomes. Since the underground stems are used for asexual reproduction, they are also diploid, and would therefore have 38 chromosomes.

Question 12

When we first see chiasmata under a microscope, we know that ________.

Accepted Answer

Chiasmata are visible structures formed during prophase I of meiosis when homologous chromosomes exchange genetic material through crossing-over. Therefore, when we first see chiasmata under a microscope, it indicates that prophase I is occurring.

Question 13

When does DNA replication take place regarding meiosis? DNA replication ________.

Accepted Answer

DNA replication occurs before meiosis I begins, during the S phase of interphase.

Question 14

What is a major difference between mitosis and meiosis I in a diploid organism?

Accepted Answer

The major difference between mitosis and meiosis I in a diploid organism is that in mitosis, sister chromatids separate, while in meiosis I, homologous pairs of chromosomes separate. This results in the formation of genetically identical daughter cells in mitosis, whereas in meiosis I, daughter cells are genetically diverse due to the separation of homologous pairs of chromosomes. Option A correctly states this difference. Option B is incorrect because homologous pairs of chromosomes separate in meiosis I, not meiosis II. Option C is incorrect because DNA replication takes place before both mitosis and meiosis I. Option D is incorrect because meiosis I results in daughter cells that are genetically diverse, not identical.

Question 15

Centromeres split and sister chromatids migrate to opposite poles in ________ of meiosis.

Accepted Answer

In anaphase II of meiosis, the centromeres of each chromosome split, allowing the sister chromatids to migrate to opposite poles. This is a key difference from anaphase I, where homologous chromosomes, rather than sister chromatids, are separated.

Question 16

The chromosome number of hexaploid wheat, Triticum aestivum, can be represented as ________.

Accepted Answer

Hexaploid wheat, Triticum aestivum, has six sets of chromosomes, hence its chromosome number is represented as 6n.

Question 17

What phase of meiosis is seen in the accompanying figure?

Accepted Answer

The answer of  What phase of meiosis is seen...

Question 18

For a species with a haploid number of 23 chromosomes, how many different combinations of maternal and paternal chromosomes are possible for the gametes?

Accepted Answer

For a haploid number of 23 chromosomes, each gamete will have a different combination of maternal and paternal chromosomes. The total number of possible combinations is 2^23, which is approximately 8 million.

Question 19

If a horticulturist breeding gardenias succeeds in having a single plant with a particularly desirable set of traits, which of the following would be her most probable and efficient route to establishing a line of such plants?

Accepted Answer

Cloning the plant would be the most efficient route to establishing a line of plants with the same desirable traits, as the cloned plants would be genetically identical to the original plant. Backtracking through previous experiments or forcing the plant to self-pollinate may not lead to the same desirable traits, and breeding with a plant with weaker traits would dilute the desirable traits. Adding nitrogen to the soil may affect the plant's growth but would not necessarily ensure the continuation of the desirable traits.

Question 20

If meiosis produces haploid cells, how is the diploid number restored for those organisms that spend most of their life cycle in the diploid state?

Accepted Answer

Organisms that spend most of their life cycle in the diploid state restore their diploid number through fertilization, which involves the fusion of haploid gametes (sperm and egg) to form a diploid zygote.

Quiz 13: Meiosis