Download ANSWERS Pitts` Biology 110 review: genetics 1

ANSWERS Pitts’ Biology 110 review: genetics
1. Chromosomes contain information for building proteins.
2. SHARE - Proteins are used several ways in living cells. Some protein molecules are used in the
construction of cells and tissues. Most enzymes are composed of proteins. Other proteins have special
functions; for example, hemoglobin is a protein whose primary function is to transport oxygen in the
bloodstream.
3a. Enzymes control the rates at which most chemical reactions occur in living cells. Generally, a reaction
will not occur (or will not occur fast enough to produce a significant amount of the product) if an enzyme is
not present to increase the speed of the reaction.
3b. Enzymes determine which chemical reactions occur in a cell. These reactions, in turn, determine the
size, shape, and activities of each cell. In effect, enzymes determine each of our characteristics. “We are
what we are because of our enzymes.”
4. Each enzyme can usually influence only one specific chemical reaction (but an enzyme may be used
millions of times for this reaction).
5. Each enzyme has areas (called active sites) where the reacting molecules (which are called substrates)
attach. Since the active sites have specific shapes, only certain molecules can attach and be involved in the
reaction regulated by that enzyme.
6. Chromosomes primarily contain deoxyribonucleic acid (DNA) molecules and protein molecules.
7. The information for constructing proteins is stored in the deoxyribonucleic acid (DNA) molecules.
8. The number of chromosomes present in a cell will depend on whether the cell is a somatic cell (= body
cell) or a gamete (= egg or sperm).
9. A gamete is a type of sex cell that is used for sexual reproduction. A gamete contains only one of each
kind of chromosome, unlike body cells (e.g., liver cells, skin cells, muscle cells) which contain two of each
kind of chromosome. Two types of gametes are egg and sperm.
10. Each human gamete (i.e., egg or sperm) will normally contain 23 chromosomes.
11. A human gamete will normally have 23 different kinds of chromosomes.
12. A human gamete will normally have one of each kind of chromosome.
13. The term “haploid” is used to describe a cell that has one of each kind of chromosome.
14. Two examples of human cells that are haploid are egg and sperm.
15. Another term used to describe a haploid cell is “1N” or “N.”
16. A 1N (= haploid) human cell would contain 23 chromosomes.
17. The term “diploid” refers to a cell that has two of each kind of chromosome that is normally found in
that species. This cell can also be described as being “2N.”
18. A diploid human cell contains a total of 46 chromosomes, two of each of the 23 different kinds.
19. All of the cells in a human except the eggs and sperm are normally diploid.
20. The process of meiosis is involved in the production of gametes.
21. The process of meiosis reduces chromosome numbers by 1/2. Normally, the cell which enters meiosis is
a germ cell which is 2N. This chromosome number is reduced to 1N (= N) in each of the gametes that is
produced.
22. Since the germ cell is diploid, it has two copies of chromosome No. 1. Let's refer to them as 1' and 1”.
Each gamete is going to have one copy of chromosome No. 1. Either copy of chromosome No. 1 could be
in a gamete. Pure chance determines which chromosome goes into a particular gamete. That is, about 50%
of the gametes would have chromosome 1' and the other 50% of the gametes would have chromosome 1”.
23. The term “homologous” is used to describe two chromosomes that control the same characteristics.
24. The term “gene” is used to describe the part of a chromosome that controls or influences one
characteristic.
25. The number of genes present on a chromosome depends, in part, on the length of the chromosome and
the length of each gene. Chromosomes, like books, differ in length. The number of genes present on a
chromosome, like the number of pages in a book, may be small or large.
26. Some 50,000 to 100,00 human traits are thought to be genetically influenced.
27. At least one gene influences each trait; therefore, at least 75,000 genes would be present. However,
some traits, such as height, are influenced by several sets of genes so the total could be well over 75,000.
28. The goal of the workers in the Human Genome Project is to prepare a “map” of each of the 23 different
kinds of human chromosomes. This map would show the position and size of each gene. Each gene would
be analyzed and the sequence of nucleotides in it would be determined.
29. The information storing molecule in a gene is deoxyribonucleic acid (DNA).
30. A chromosome is a cell organelle that contains genetic information in a molecule called
deoxyribonucleic acid (DNA); the sections of DNA that control specific traits are called genes.
31. The term “alleles” is used to describe genes that control or influence the same characteristic.
32. A diploid human cell would possess at least two genes for each trait. For example, if Chromosome No.
4' has a gene that influences eye color, then its homologue, Chromosome No. 4”, would also have a similar
gene at the same location. (Remember, since this is a diploid cell, two of each kind of chromosome would
be present in the cell.) Since these two genes influence the same trait, they would be alleles.
33. No. Two genes that influence the same trait would be called alleles but they do NOT have to be
identical. For example, one gene might have information that produces brown eyes, while another gene
might have information that produces blue eyes. These two genes could still be called alleles even though
they are not identical.
34. No. Since they influence different traits they are not alleles. All of the genes influencing eye color could
be called alleles, and all of the genes influencing hair color could be called alleles. But describing the gene
for eye color and the gene for hair color as alleles would be as incorrect as saying that two females with
different mothers and different fathers are sisters.
35. The term “homozygous” means that two alleles (= genes controlling the same characteristic) in a
diploid cell are identical. For example, in a diploid cell that is described as being homozygous the two
genes for eye color may both have information for blue eyes, or they may both have information for brown
eyes.
36. The term “heterozygous” means that a diploid cell has two slightly differing alleles for a specific trait.
For example, one of the alleles for eye color might have information for brown eyes and the other allele
might have information for blue eyes.
37. In a diploid cell that is heterozygous for a particular trait, one of the two alleles will be used (=
“expressed”) while the other allele is not used. For example, if the cell has one allele for brown eyes and
one allele for blue eyes, the allele for brown will be used and the allele for blue will not be used. Therefore,
the allele for brown is dominant over the allele for blue.
38. In a diploid cell that is heterozygous for a particular trait, the allele that is not used is said to be
recessive. For example, in question 37 the allele for brown eye color is used but the allele for blue eye color
is not used. The allele for brown is “dominant,” and the allele for blue is “recessive.”