Genetics: 3-3 & 3-4
Q: Define meiosis.
A: A process in cell division during which the number of chromosomes decreases to half the original number by two divisions of the nucleus, which results in the production of sex cells
Q: If an organism is hybrid for a certain gene -- for example, a pea plant hybrid for flower color, Pp -- what percentage of that organism's sex cells will have the P allele?
A: 50%
Q: What is the relationship between a gene, a DNA molecule, and a protein?
A: A gene is the part of a DNA molecule that codes for a certain protein.
Q: When is a mutation considered harmful?
A: A mutation is considered harmful when it decreases an organism's ability to survive to reproduce.
Q: List the sequence of events that happens during protein synthesis.
A: A section of DNA unzips; messenger RNA is produced using one strand of that DNA section as a pattern; the mRNA moves into the cytoplasm where it attaches to a ribosome; a tRNA molecule that can pair with the first code word in the mRNA carries an amino acid to the ribosome; a second tRNA molecule that pairs with the next code word in the mRNA carries the appropriate amino acid to the ribosome; a bond forms between the two amino acids; the first tRNA releases from the ribosome and goes to pick up another amino acid; the ribosome moves down the mRNA molecule; another tRNA comes over carrying the next amino acid; and the process continues until the "stop" signal is reached.
Q: A new mutation in mice causes the coat to be twice as thick as normal. In what environments would this mutation be helpful, and why?
A: A thicker coat would be a helpful mutation in a cold environment, because it provides more insulation to keep the mouse warm.
Q: How long are the "words" of the DNA code?
A: All the "words" of the DNA code are three nitrogen bases (three "letters") long.
Q: During meiosis, when do sister chromatids separate?
A: Anaphase 2.
Q: What is the relationship between genes and chromosomes?
A: Chromosomes are made up of DNA; genes are made up of sections of this DNA.
Q: How many different amino acids can a single tRNA pick up?
A: Each tRNA is specific to one and only one amino acid.
Q: What has to happen before meiosis can begin?
A: Every chromosome in the parent cell is copied (during interphase).
Q: True or False: A typical chromosome holds about a dozen or so genes.
A: FALSE - a single chromosome may hold hundreds or even thousands of genes.
Q: True or False: In RNA, uracil bonds with thymine.
A: FALSE - uracil bonds with adenine.
Q: True or False: Each of the 64 possible combinations for DNA code words codes for a unique amino acid.
A: FALSE. Although there are 64 possible 3-"letter"-long combinations of 4 bases, there are only 20 amino acids. Many of the 64 "words" of the DNA code are "synonyms," with several combinations coding for the same amino acid.
Q: True or false: Both DNA & RNA can be found inside the cytoplasm.
A: FALSE. DNA is kept inside the nucleus, were it is protected from being damaged.
Q: True or False: Mutations are always harmful.
A: False. Mutations can be harmful, helpful, or neutral.
Q: State the chromosome theory of inheritance.
A: Genes are carried from parents to their offspring on chromosomes.
Q: How does a mutation in a gene cause a change in an organism's phenotype?
A: If the mutation causes a change in the protein that is produced by the gene, the phenotype of the organism may be changed.
Q: Why is meiosis necessary for organisms that reproduce sexually?
A: Meiosis is necesssary for organisms that reproduce sexually because when two sex cells combine, if chromosome number was not reduced in half by meiosis, the resulting fertilized egg would have double the normal chromosome number.
Q: Where is messenger RNA made?
A: Messenger RNA is made inside the nucleus.
Q: Compare the results of mitosis and meiosis.
A: Mitosis results in two daughter cells that are identical to each other and to the parent cell. Meiosis results in four daughter cells, each of which is genetically different both from each other and from the parent cell. Part of this difference is due to the daughter cells of meiosis having half as many chromosomes as the parent cell, while the daughter cells of mitosis have the same number of chromosomes as the parent cell.
Q: Why are mutations in an organism's body cells not passed on to their offspring?
A: Mutations in body cells do not affect sex cells. Only sex cells carry alleles to offspring.
Q: What happens to mRNA once it is formed in the nucleus?
A: Once formed in the nucleus, mRNA exits the nucleus through nuclear pores and heads out to a ribosome in the cytoplasm.
Q: What is the relationship between alleles and chromosomes?
A: Paired alleles are carried on paired chromosomes.
Q: Identify three differences between DNA and RNA.
A: RNA is single-stranded while DNA is double-stranded; the sugar in RNA's sugar-phosphate "backbone" is ribose, while in DNA's sugar-phosphate "backbone," the sugar is deoxyribose; and the four bases in RNA are adenine, cytosine, guanine, and uracil, while in DNA they are adenine, cytosine, guanine, and thymine.
Q: True or False: Genes are responsible for the production of proteins.
A: TRUE
Q: True or False: both DNA & RNA have a sugar-phosphate backbone.
A: TRUE, although the sugars are different (ribose for RNA & deoxyribose for DNA), and RNA is single-stranded while DNA is double-stranded.
Q: True or False: During protein synthesis, after the DNA molecule unzips, messenger RNA is copied off of one strand of DNA.
A: TRUE. (Only 1 of the 2 strands is used as a template for the mRNA.)
Q: True or false: Both DNA & RNA can be found inside the nucleus.
A: TRUE. (Remember, messenger RNA is made in the nucleus, using a piece of DNA as its pattern.)
Q: What determines the genetic code?
A: The order of nitrogen bases along a gene determines the genetic code.
Q: What is the first step in protein synthesis?
A: The portion of the DNA molecule where the gene is found has to "unzip" so that mRNA can be made using the gene's bases as its pattern.
Q: True or False: For a mutation to be passed on to offspring, it must occur in a sex cell.
A: True.
Q: Who is credited with identifying chromosomes as the structure that carries Mendel's "factors" from parents to offspring?
A: Walter Sutton
Q: The order of the bases along a gene determines the order in which __________________________.
A: amino acids are joined together to make a protein.
Q: The sequence of bases on a gene codes for the sequence of ___________________ in a _______________.
A: amino acids; protein
Q: During which part of meiosis (1 or 2) is the number of chromosomes of the dividing cell(s) reduced?
A: at the end of meiosis 1.
Q: When are the chromosomes copied for meiosis?
A: beginning of the process -- during interphase, when the cell is preparing to enter meiosis.
Q: After meiosis takes place, the process that restores the normal chromosome number is _______________.
A: fertilization
Q: The sex cells of an organism have ____________________ chromosomes as the body cells of that organism.
A: half as many
Q: What carries the DNA code out of the nucleus and into the cytoplams?
A: messenger RNA (mRNA)
Q: To which category of organic compounds do both DNA and RNA belong?
A: nucleic acids
Q: Where are genes located?
A: on chromosomes
Q: What carries amino acids over to ribosomes to be joined into a protein molecule?
A: transfer RNA (tRNA)
