Question 1

Some common domesticated fruit plants, including seedless watermelon and banana, are triploids. The seeds are small because most are genetically abnormal and do not undergo complete development. Why are most of the seeds genetically abnormal? (Hint: In normal meiosis, the chromosomes form pairs.)

Accepted Answer

Triploid plants have three sets of chromosomes instead of the usual two sets in diploid plants. This means that during meiosis, the chromosomes cannot form proper pairs, leading to errors in chromosome distribution and resulting in genetically abnormal seeds, which are usually small and don't undergo complete development.

Question 2

Among human embryos that are unable to complete development, some have three complete copies of the nuclear genome and others have four complete copies of the nuclear genome. How many chromosomes do cells of these embryos possess, respectively?

Accepted Answer

Human cells normally have 23 pairs of chromosomes, for a total of 46. When an embryo has three complete copies of the nuclear genome, it has a total of 69 chromosomes (23 x 3). When an embryo has four complete copies of the nuclear genome, it has a total of 92 chromosomes (23 x 4). Therefore, the answer is C.

Question 3

The C-value paradox applies to:

Accepted Answer

The C-value paradox refers to the lack of correlation between genome size and organismal complexity in eukaryotes. It does not apply to viruses, archaea, or bacteria.

Question 4

Artificial chromosome doubling can be induced by means of chemicals that prevent the spindle from forming or functioning normally. A certain species of grass has seven pairs of chromosomes. How many chromosomes are present after one round of artificial chromosome doubling? After two rounds of chromosome doubling?

Accepted Answer

After one round of chromosome doubling, the number of chromosomes doubles from 14 to 28. After a second round, it doubles again from 28 to 56.

Question 5

Which of the following statements applies to transposable elements?

Accepted Answer

All of the statements apply to transposable elements. Some transposable elements are capable of replicating and inserting themselves into another location in the genome, which can lead to an increase in copy number over generations. Transposable elements account for a significant fraction of the human genome, and some types can transpose via an RNA intermediate. Therefore, the best choice is E, as all of these options are correct.

Question 6

The region of DNA sequences before the start of a gene is often called the promoter. One type of promoter is called the TATA box. Many species' promoters are TATA boxes or a variation of the TATA box. DNA sequences that are similar in different organisms are called _____ sequences.

Accepted Answer

Similar DNA sequences in different organisms are referred to as conserved sequences.

Question 7

Which of the following are sequence motifs?

Accepted Answer

Sequence motifs are short, recurring patterns of nucleotides that are found in DNA or RNA sequences. Promoters, coding regions, open reading frames, and hairpin structures are all examples of sequence motifs.

Question 8

A diploid plant species has 16 chromosomes. How many chromosomes are in a tetraploid "version" of this plant? In the hexaploid? In the octoploid? (Hint: "Tetra" refers to four, "hexa" to six, and "octo" to eight.)

Accepted Answer

A tetraploid has four sets of chromosomes, so it would have 4 x 16 = 64 chromosomes. A hexaploid would have 6 x 16 = 96 chromosomes, and an octoploid would have 8 x 16 = 128 chromosomes. Therefore, the best choice is D.

Question 9

Polyploids with an odd number of sets of chromosomes have many problems in meiosis but none in mitosis. Why?

Accepted Answer

Polyploids with an odd number of sets of chromosomes have problems in meiosis because the homologous chromosomes cannot pair up properly, leading to unbalanced gametes. However, in mitosis, there is no need for homologous chromosome pairing, so the polyploid can divide normally without any problems.

Question 10

A polyploid plant is identified that has phenotypes similar to two different diploid plants species found nearby. Which of the following would support the idea that the polyploid plant is a hybrid of the two diploid species?

Accepted Answer

The number of chromosomes in the polyploid plant being the sum of the chromosomes from the two diploid plants supports the idea of hybridization, indicating that it contains genetic material from both parent species.

Question 11

The C-value paradox states that genome size:

Accepted Answer

The C-value paradox refers to the observation that genome size does not correlate with the organism's complexity, meaning that more complex organisms do not necessarily have larger genomes than simpler ones.

Question 12

A retrotransposon known as Alu1 is about 300 base pairs in length and is present in the human genome in about 1 million copies. Approximately what percentage of the human genome is accounted for by this transposon?

Accepted Answer

The answer of A retrotransposon known as Alu1 is about...

Question 13

The marbled lungfish has a genome size almost 50 times larger than that of the human genome. The MOST likely explanation is that the lungfish:

Accepted Answer

The presence of repetitive DNA is the most likely explanation for a genome size that is much larger than expected. This is because repetitive DNA sequences can account for a significant proportion of the total genome size.

Question 14

A diploid species of plant with 22 chromosomes has a tetraploid relative with 44. How many chromosomes are present in the reproductive cells of each species?

Accepted Answer

Reproductive cells, or gametes, are haploid, meaning they contain half the number of chromosomes found in somatic (body) cells. Therefore, the diploid species' gametes have 11 chromosomes (half of 22), and the tetraploid species' gametes have 22 chromosomes (half of 44).

Question 15

Which of the following contribute to the C-value paradox illustrated in Figure 13.8 below?

Accepted Answer

The C-value paradox refers to the fact that genome size does not necessarily correlate with an organism's complexity. Choices B, D, and E all contribute to this paradox because they illustrate that genome size is not simply a reflection of the amount of genetic information needed for an organism's development and function. Non-coding DNA (choice B), transposable elements (choice D), and repetitive DNA (choice E) do not directly contribute to the organism's phenotype, yet they can significantly impact genome size. This means that organisms with similar levels of developmental and functional complexity can have vastly different genome sizes, leading to the C-value paradox.

Question 16

The estimated number of genes in the human genome is:

Accepted Answer

The current estimated number of protein-coding genes in the human genome is approximately 25,000. This is a revision from the earlier estimation of 20,000-25,000 genes. While there is still ongoing research and debate about the exact number, the most recent estimate is closest to 25,000.

Question 17

The vast majority of naturally occurring polyploids have an even number of sets of chromosomes.

Accepted Answer

This is true. The majority of naturally occurring polyploids have an even number of sets of chromosomes because they usually result from hybridization between two diploid parent species.

Question 18

Two viruses with genomes of double-stranded DNA are compared and one has a genome size two times as big as the other. This is likely because the one with the larger genome:

Accepted Answer

The size of a genome is usually related to the number of genes it contains. Therefore, the virus with the larger genome is likely to have more genes than the one with the smaller genome.

Question 19

Various species of the flowering plant Chrysanthemum have 18, 36, 54, 72, and 90 chromosomes. The variation is likely due to:

Accepted Answer

The variation in the number of chromosomes in Chrysanthemum species is likely due to polyploidy, which occurs when an organism has multiple sets of chromosomes. This can occur through hybridization events or errors during cell division, and can result in an increase in the number of chromosomes in an individual.

Question 20

Complex organisms can be characterized as having a:

Accepted Answer

The answer of Complex organisms can be characterized as having...

Quiz 13: Genomes