Learn Genetics Online: Cell Division

1. The 23rd set of chromosomes are the sex chromosomes, because they determine gender. A typical human female will have two X chromosomes, or XX. On the other hand, a typical human male will only have one X chromosome and one ______ chromosome.

Human males are XY. The Y chromosome has the information to build the male reproductive system. The X chromosome is found in all humans because it has information to build many different parts of the body, including the female reproductive system. When Y is present, the information in X to build the female reproductive system is "canceled out."

Explanation

Human males are XY. The Y chromosome has the information to build the male reproductive system. The X chromosome is found in all humans because it has information to build many different parts of the body, including the female reproductive system. When Y is present, the information in X to build the female reproductive system is "canceled out."

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2. A eukaryotic cell, such as a human cell, is larger than a prokaryotic cell, such as a bacterium.

True

False

Eukaryotes are larger than prokaryotes. Eukaryotes are larger because they have organelles and a nucleus inside of them, whereas prokaryotes are much more simple and do not keep their DNA in a nucleus and do not have organelles. This is visible on the "cell size and scale" activity.

Explanation

Eukaryotes are larger than prokaryotes. Eukaryotes are larger because they have organelles and a nucleus inside of them, whereas prokaryotes are much more simple and do not keep their DNA in a nucleus and do not have organelles. This is visible on the "cell size and scale" activity.

3. In DNA replication, what is the name of the enzyme that adds in complementary nucleotides?

DNA helicase

DNA ligase

DNA polymerase

DNA polymerase is the enzyme that adds in new complementary bases, using base-pairing rules. You can remember this because in Replication we are building a DNA polymer - the word polymer means "large molecule." A polymerase is basically a "polymer-maker"

Explanation

DNA polymerase is the enzyme that adds in new complementary bases, using base-pairing rules. You can remember this because in Replication we are building a DNA polymer - the word polymer means "large molecule." A polymerase is basically a "polymer-maker"

4. Match each of the vocabulary terms associated with genetics to its correct definition.

DNA

Chromosome

Gene

Protein

Trait

From "tour of the basics". If you missed these, please go back and review this section again.

Explanation

From "tour of the basics". If you missed these, please go back and review this section again.

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5. Which of the following correctly displays complementary base-pairing of DNA nucleotides?

A always bonds with G, and C always bonds with T.

A always bonds with C, and G always bonds with T.

A always bonds with T, and C always bonds with G.

None of the above are true.

All of the above are true.

Please review "tour of the basics" and "build a DNA molecule" if you got this question incorrect.

Explanation

Please review "tour of the basics" and "build a DNA molecule" if you got this question incorrect.

6. All living things have 46 chromosomes.

True

False

False - humans have 46 but other organisms may have more or less DNA. For example, a giant sequoia tree has 22 chromosomes, a fly has only 8, and a carp (type of fish) has 104! Notice that all of these numbers are even: that is because all of these organisms are diploid, meaning that they have 2 sets of chromosomes. (One set from each parent)

Explanation

False - humans have 46 but other organisms may have more or less DNA. For example, a giant sequoia tree has 22 chromosomes, a fly has only 8, and a carp (type of fish) has 104! Notice that all of these numbers are even: that is because all of these organisms are diploid, meaning that they have 2 sets of chromosomes. (One set from each parent)

7. Check ALL of the statements which are true about DNA.

DNA encodes a detailed set of plans, like a blueprint, for building different parts of the cell.

DNA stands for DeoxyRibonucleic Acid.

DNA lives in the nucleus of the cell, but is permitted to leave as necessary.

The DNA molecule comes in the form of a twisted ladder shape called a "double helix".

All are true of DNA except that DNA is actually NOT allowed to leave the nucleus. The information encoded in DNA is so important that it is "held captive" inside the nucleus to keep it safe from destruction or mutation.

Explanation

All are true of DNA except that DNA is actually NOT allowed to leave the nucleus. The information encoded in DNA is so important that it is "held captive" inside the nucleus to keep it safe from destruction or mutation.

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8. Check ALL of the statements which are true about a human sperm cell.

Sperm cells have the same amount of DNA as any other human cell.

Sperm cells contain just one copy of each of the 23 human chromosomes.

The head of a sperm cell is almost all nucleus to make it a more efficient swimmer.

The human sperm cell is approximately the same size as a human egg cell.

Sperm cells are gamete (sex) cells and are haploid - meaning they only have one copy of each of the 23 human chromosomes. This is important because in reproduction a sperm cell will join with an egg cell, which is also haploid, thus joining each set of 23 chromosomes to make 46 total (diploid) needed to make a baby. The head of a sperm cell is almost all nucleus because much of the cytoplasm has been squeezed out - this makes the sperm cell a much more efficient swimmer to deliver the DNA to the egg cell. These answers can be found in the "Cell Size and Scale" activity.

Explanation

Sperm cells are gamete (sex) cells and are haploid - meaning they only have one copy of each of the 23 human chromosomes. This is important because in reproduction a sperm cell will join with an egg cell, which is also haploid, thus joining each set of 23 chromosomes to make 46 total (diploid) needed to make a baby. The head of a sperm cell is almost all nucleus because much of the cytoplasm has been squeezed out - this makes the sperm cell a much more efficient swimmer to deliver the DNA to the egg cell. These answers can be found in the "Cell Size and Scale" activity.

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9. Which of the following do scientists use to "read" a set of chromosomes? (Check all that apply)

Size

Banding Pattern

Centromere Position

All three are very important in "reading" a chromosome. Please review "How do scientists read chromosomes"

Explanation

All three are very important in "reading" a chromosome. Please review "How do scientists read chromosomes"

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10. Check all of the following that are true about DNA replication:

DNA replicates in both directions.

DNA Polymerase uses complementary base-pairing rules to add in new nucleotides.

DNA replication happens in the cytoplasm.

DNA replication happens after cell division.

DNA replication happens in the NUCLEUS, not cytoplasm. DNA is not allowed to leave the nucleus, so all processes involving DNA will occur in the nucleus. Also, DNA replication happens BEFORE cell division, so the cell temporarily doubles its DNA before dividing so that each new cell gets the correct amount. From the "DNA Replication" activity from phschool.

Explanation

DNA replication happens in the NUCLEUS, not cytoplasm. DNA is not allowed to leave the nucleus, so all processes involving DNA will occur in the nucleus. Also, DNA replication happens BEFORE cell division, so the cell temporarily doubles its DNA before dividing so that each new cell gets the correct amount. From the "DNA Replication" activity from phschool.

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