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BIOL 121 Unit II Study Guide
- Bacteria have circular chromosomes and divide by binary fission. Eukaryotic species have linear
chromosomes and divide by mitosis or meiosis.
- A nucleosome is made up of eight histone proteins (two H2a, two H2b, two H3, and two H
histone proteins) and two rounds of DNA double helix wrapping around those eight histone core
proteins. Nucleosome is a feature of the chromosomes of eukaryotic but not prokaryotic
species.
- The mitotic phase alternates with interphase in the cell cycle. DNA replication takes place in the
S phase of interphase. Interphase (G1, S, and G2 phases) takes much longer than mitotic phase
(prophase, metaphase, anaphase, telophase, and cytokinesis) for cells to complete. Centrosome
duplication starts at the end of G1 and the beginning of S. The duplication is complete at G2.
Nuclear membrane fragments at the end of prophase but reappears at telophase.
Centrosome duplication (https://www.cell.com/fulltext/S0092-8674(01)00366-X)
- Centrosome is a microtubule organizing structure. It is replicated in the interphase of cell cycle.
Centromere on the other hand is a waist structure of duplicated chromosome where
kinetochore is formed.
- Microtubules form spindle structures during mitosis and meiosis. They are formed by α-tubulin
and β-tubulin proteins through a process called polymerization. Microtubules grow out from
centrosome and connect to kinetochore of duplicated chromosomes. The separation of sister
chromatids is achieved by depolymerization of microtubules from the kinetochore side and
degradation of cohesin proteins.
- Homologous chromosomes are in general of the same length. If one of each pair of homologous
chromosomes is inherited from the mother, the other of the pair must be from the father. The
genes on homologous chromosomes are in general in the same sequential order but can be in
different forms called alleles. Duplicated homologous chromosomes form tetrads during
prophase I of meiosis.
- A chromatid is a replicate chromosome.
- Sister chromatids are the two chromatids of a replicated chromosome.
- Mitosis can happen in both somatic cells and reproductive cells. But meiosis only happens to
reproductive cells that will form gametes.
- A zygote divides by undergoing mitosis to form two daughter cells, which will divide further to
form a multi-cell embryo.
- How many chromosomes are there in a human somatic cell? How many chromosomes are there
in a human egg or sperm?
- What is the difference between the processes of cytokinesis of plants and animals?
- What is the name for bacterial cell division?
- In which cells microtubule spindles form within nuclear membrane?
- What protein complex holds sister chromatids together?
- What is the difference between normal cells and tumor cells with regard to their growth?
- What happens during the prophase of meiosis I?
- If a cell contains 32 chromatids at the metaphase of mitosis, how many chromosomes will each
daughter cell have?
- How does cyclin and cyclin-dependent kinase protein complex work in cell cycle?
- In which cell division (mitosis or meiosis) can you see crossing over or tetrads formation?
- What protein associates with Cdk to form a catalytically active complex in cell cycle progression?
- Each round of mitosis produces two genetically identical daughter cells while each round of
meiosis through meiosis I and II produces four genetically different daughter cells.
- When crossing an organism that is homozygous recessive for a single trait with a heterozygote,
what is the chance of producing an offspring with the homozygous recessive phenotype?
- Black fur in mice ( B ) is dominant to brown fur ( b ). Short tails ( T) are dominant to long tails ( t ).
What fraction of the progeny of the cross BbTt × BBtt will have black fur and long tails?
- Radish flowers may be red, purple, or white. A cross between a red-flowered plant and a white-
flowered plant yields all-purple offspring. The part of the radish we eat may be oval or long, with
long being the dominant characteristic. If true-breeding red long radishes are crossed with true
breeding white oval radishes, what will be the phenotype of F1 generation?
- In snapdragons, heterozygotes for one of the genes have pink flowers, whereas homozygotes
have red or white flowers. When plants with red flowers are crossed with plants with white
flowers, what proportion of the offspring will have pink flowers?
- In cattle, roan coat color (mixed red and white hairs) occurs in the heterozygous ( Rr ) offspring of
red ( RR ) and white ( rr ) homozygotes. What crosses would produce offspring in the ratio of 1
red : 2 roan : 1 white?
- Huntington's disease occurs only under a dominant heterozygous condition with late age of
onset in humans. If one parent has the disease, what is the probability that his or her child will
have the disease?
