GRE Subject Test: Biology › Chromatin and Chromosomes
Human beings have diploid cells. What is indicated by this statement?
Humans have homologous chromosome pairs
Humans have both sex chromosomes and somatic chromosomes
Humans have two chromosomes in each cell nucleus
Humans have two stages of cell division
Human beings have somatic (body) cells that are diploid. This means that each cell has two copies of each of the 23 chromosomes: one from the father and one from the mother. As a result, the karyotype of a human being would show 23 pairs of chromosomes, for a total of 46. Diploid cells contain two non-identical copies of the same genes. All diploid cells will contain two separate alleles for each gene in the genome, represented by the two homologous chromosomes.
An important note to make is that human germ (sex) cells are haploid, meaning that the chromosomes are not paired in sperm cells and egg cells.
Human beings have diploid cells. What is indicated by this statement?
Humans have homologous chromosome pairs
Humans have both sex chromosomes and somatic chromosomes
Humans have two chromosomes in each cell nucleus
Humans have two stages of cell division
Human beings have somatic (body) cells that are diploid. This means that each cell has two copies of each of the 23 chromosomes: one from the father and one from the mother. As a result, the karyotype of a human being would show 23 pairs of chromosomes, for a total of 46. Diploid cells contain two non-identical copies of the same genes. All diploid cells will contain two separate alleles for each gene in the genome, represented by the two homologous chromosomes.
An important note to make is that human germ (sex) cells are haploid, meaning that the chromosomes are not paired in sperm cells and egg cells.
What is a nucleosome?
A repeating unit of chromatin
A membrane-bound organelle that contains epigenetic information
Non-chromosomal DNA that is free floating in the cytosol
A complex of proteins that controls nuclear import
Nucleosomes are the basic, repeating units of eukaryotic chromatin. They consist of chromosomal DNA wrapped around special DNA-binding proteins called histones. There are many examples of non-chromosomal DNA, such as plasmids, but they do not contain nucleosomes. Nuclear import is controlled by importin proteins.
What is a nucleosome?
A repeating unit of chromatin
A membrane-bound organelle that contains epigenetic information
Non-chromosomal DNA that is free floating in the cytosol
A complex of proteins that controls nuclear import
Nucleosomes are the basic, repeating units of eukaryotic chromatin. They consist of chromosomal DNA wrapped around special DNA-binding proteins called histones. There are many examples of non-chromosomal DNA, such as plasmids, but they do not contain nucleosomes. Nuclear import is controlled by importin proteins.
Which answer choice incorrectly matches the type of chromatin with the phase of mitosis?
Euchromatin—telophase
Euchromatin—interphase
Heterochromatin—interphase
Heterochromatin—metaphase
Heterochromatin—prophase
DNA is stored in loosely wound euchromatin before mitosis. During mitosis, the DNA condenses into chromosomes, which are made of heterochromatin. It becomes more dense during prophase, and stays that way until the end of mitosis. Euchromatin is more lightly packed than heterochromatin.
Mitosis follows the following sequence: prophase, metaphase, anaphase, telophase, cytokinesis. Interphase refers to the time period between mitotic divisions. During interphase, most DNA is euchromatin, but some regions remain as heterochromatin to prevent unwanted transcription; thus DNA exists as both types of chromatin during interphase, but only as heterochromatin during mitosis. Matching euchromatin to telophase is the answer, as this is a false statement.
Which answer choice incorrectly matches the type of chromatin with the phase of mitosis?
Euchromatin—telophase
Euchromatin—interphase
Heterochromatin—interphase
Heterochromatin—metaphase
Heterochromatin—prophase
DNA is stored in loosely wound euchromatin before mitosis. During mitosis, the DNA condenses into chromosomes, which are made of heterochromatin. It becomes more dense during prophase, and stays that way until the end of mitosis. Euchromatin is more lightly packed than heterochromatin.
Mitosis follows the following sequence: prophase, metaphase, anaphase, telophase, cytokinesis. Interphase refers to the time period between mitotic divisions. During interphase, most DNA is euchromatin, but some regions remain as heterochromatin to prevent unwanted transcription; thus DNA exists as both types of chromatin during interphase, but only as heterochromatin during mitosis. Matching euchromatin to telophase is the answer, as this is a false statement.
Which of the following are not observed when performing a karyotype?
Gene loci
Position of centromeres
Number of chromosomes
Size of chromosomes
Differences in satellite chromosome position and number
Karyotypes describe whole chromosome structure, including the number and size of chromosomes, position of centromeres, distribution of heterochromatin versus euchromatin, and the presence of satellite chromosomes that are found near the centromeres. However, a karyotype is unable to label specific gene sequences and determine their chromosomal locations. Most karyotypes depict chromosomes of a cell in metaphase.
Which of the following are not observed when performing a karyotype?
Gene loci
Position of centromeres
Number of chromosomes
Size of chromosomes
Differences in satellite chromosome position and number
Karyotypes describe whole chromosome structure, including the number and size of chromosomes, position of centromeres, distribution of heterochromatin versus euchromatin, and the presence of satellite chromosomes that are found near the centromeres. However, a karyotype is unable to label specific gene sequences and determine their chromosomal locations. Most karyotypes depict chromosomes of a cell in metaphase.
Which of the following proteins is necessary for nucleosome formation?
Histones
DNA ligase
Chromatin
Histone methyltransferases
Nuclear lamin
The correct answer is histones. DNA wraps around histones to form the nucleosomes. Further condensation of many nucleosomes results in chromatin (DNA state). Histone methyltransferases are important enzymes that modify histones during epigenetic gene regulation; however, they are not necessary for nucleosome formation. DNA ligase is responsible for catalyzing the formation of phosphodiester bonds, but is unrelated to nucleosome formation.
Which of the following proteins is necessary for nucleosome formation?
Histones
DNA ligase
Chromatin
Histone methyltransferases
Nuclear lamin
The correct answer is histones. DNA wraps around histones to form the nucleosomes. Further condensation of many nucleosomes results in chromatin (DNA state). Histone methyltransferases are important enzymes that modify histones during epigenetic gene regulation; however, they are not necessary for nucleosome formation. DNA ligase is responsible for catalyzing the formation of phosphodiester bonds, but is unrelated to nucleosome formation.