Study questions for the lectures 8-9
1. The human gametes have about 3 billion bp of DNA in their chromosomes.
a. Express the size of the diploid genome in kb (kilo bases; 1kb = 1000bp)
Human gamete = haploid genome = 3 billion bp of DNA in their chromosomes
Diploid genome = 2 x 3 billion bp = 6 million kb of DNA in their chromosomes
b. If the entire DNA was in relaxed B-DNA form, what would be the average length of a
chromosome expressed in cm?
Since B-DNA is approx. 10 bp/turn and each turn is every 3.4 nm, each bp is 0.34 nm
6 billion bp / 46 chromosomes = 130 million bp/chromosome
130 million bp x 0.34 nm = 44 million nm x 10 = 4.4 cm
c. On average, how many complete turns would be in each chromosome?
4.4 cm = 44,000,000 nm
44,000,000 nm / 3.4 nm/turn = 13 million complete turns
d. If there are around 30-40,000 genes in a human gamete, how many genes are there in
an average chromosome?
If there is 30-40,000 genes and 23 chromosomes in a human gamete (haploid),
30-40,000 genes/gamete ÷ 23 chromosomes/gamete = 1304–1739
2. Define homologous chromosomes.
Chromosomes that are identical in size, shape, and banding pattern (each derived from
1 parent), and carry the same genes but may have different alleles
3. Define non-homologous chromosomes.
Chromosomes that differ in size, shape, and banding pattern, and carry different genes
4. How many homologous chromosomes are there in a germ cell of a woman? Of a man? There are 23 homologous chromosomes in the germ cell of a woman (22 homologous
autosomal chromosomes + 1 homologous sex chromosome XX)
There are 22 homologous chromosomes in the germ cell of a man (not 23 like in women
because the male sex chromosomes XY are not homologous)
5. Distinguish between homologous chromosomes and sister chromatids.
Homologous chromosomes: 2 non-identical chromosomes that match in size, shape,
and banding pattern (each derived from 1 parent); they carry the same genes but may
have different alleles
Sister chromatids: 2 identical copies of a chromosome that exist immediately after DNA
6. What is the purpose of cell division in Prokaryotes? In Eukaryotes?
Prokaryotes: the purpose of cell division is reproduction
Eukaryotes: the purpose of cell division is tissue growth and repair of damaged tissues
(via mitosis), and reproduction (via meiosis)
7. Distinguish between DNA replication and cell division.
DNA replication occurs during S phase of the cell cycle as chromosomes duplicate (in
which 2 identical copies of DNA are produced from one DNA molecule) 1 cell remains
Cell division occurs at the end of the M phase (mitosis) in which the parent cell divides
into 2 daughter cells 1 cell is split into 2 cells
8. Distinguish between reason/purpose for/of mitosis and reason/purpose for/of meiosis?
The purpose of mitosis is tissue growth and repair of damaged tissues by producing
daughter cells that are identical to the parent cell no variabiliy
The purpose of meiosis is reproduction to form gametes that are not identical to each
other or to the parent cell; the goal is to preserve information while keeping/making it
variable at the same time variability due to independent assortment of homologous
9. How is variability of genetic information attained by meiosis and fertilization? Variability in meiosis is due to independent assortment of homologous chromosomes
(different arrangements of chromosomes at metaphase I and II in meiosis)
Variability is also due to crossing over of homologous chromosomes in prophase I during
Variability of genetic information occurs in fertilization due to the fusion of 1 haploid cell
from the mother and 1 haploid cell from the father
10. What is a cell cycle? What are the stages of cell cycle?
The cell cycle is the orderly set of events that take place between the formation of a new
cell and the division of that “parent” cell into 2 new “daughter” cells
Stages of the cell cycle:
o G 1hase: cell growth occurs as organelles double (chromosomes are unipartite)
o S phase: DNA replication occurs as chromosomes duplicate (chromosomes are
o G 2hase: cell growth occurs as cell prepares to divide