WEEK 3: Mitosis & Meiosis (LAB) Flashcards
DNA
- where the bulk of information required to generate any individual for more organisms
- the amount of DNA depends on the species
Chromosome
A chromosome is a single, linear molecule of DNA that is packaged with histone proteins into a compact structure and serves as the genetic material of an organism. A structure consisting of DNA and associated proteins that carry and transmit genetic information.
- count chromosomes by counting the centromere
Chromosomes are the packaging system used by eukaryotes; a chromosome consists of a molecule of DNA wrapped around and associated with various proteins. There are two different types of packaging:
- loose packaging
- tight packaging
Loose Packaging
DNA is wrapped around histone proteins; both DNA replication and transcription require loose packaging.
- Looks like “beads on a string” when we look at DNA wound on nucleosomes
Nucleosomes
The basic repeating unit of chromatin, consists of a core of eight histone proteins (two each of H2A, H2B, H3, and H4) and about 146 bp of DNA that wraps around the core about two times.
Chromatin
The material found in the eukaryotic nucleus; consists of DNA and histone proteins.
Histone
Low-molecular-weight proteins found in eukaryotes that associate closely with DNA to form chromosomes.
Tight Packaging
Highly condensed chromosome; the transmission of DNA into new cells (cell division) requires a high level of packaging.
Telomere
Stable end of a eukaryotic chromosome.
Centromere
Constricted region on a chromosome that stains less strongly than the rest of the chromosome; serves as the attachment point for spindle microtubules.
- A constricted region of a chromosome where spindle fibres attach
- Moderately repetitive DNA in heterochromatin form
- Chromosome fragments that lack centromeres are lost in mitosis
Metacentric Chromosome
Chromosomes in which the two chromosome arms are approximately the same length.
Acrocentric Chromosomes
Chromosome in which the centromere in near one end, producing a long arm at one end and a knob, or satellite, at the other end.
Telocentric Chromosomes
Chromosome in which the centromere is at or very near one end.
Gametes
In animals, gametes are the eggs and sperm cells.
- Gametes are haploid (n) in terms of chromosome number because these cells contain half the number of chromosomes as the respective somatic cells.
- Human gametes contain 23 chromosomes and are designed as n =23 (each of these chromosomes are different)
Somatic Cells
Somatic cells are referred to as diploid (2n) because these cells have twice the number of chromosomes as the respective gametes.
- Human somatic cells (e.g., neurons, chondrocytes, white blood cells) are diploid and described 2n = 46.
- Each somatic cell contains two copies of chromosome 1, two copies of chromosome 2 and so on. We refer to the pairs of the same chromosome in diploid cells as homologous chromosomes.
Homologous Chromosome / Homologous Pair
Homologous chromosomes are pairs of chromosomes that contain the same set of genes but may have different versions of those genes (alleles).
A pair of chromosomes that are alike in structure and size and that carry the genetic information for the same set of hereditary characteristics. One chromosome of a homologous pair is inherited from the male parent, and the other is inherited from the female parent.
- Each somatic cell contains two copies of chromosome 1, two copies of chromosome 2 and so on. We refer to the pairs of the same chromosome in diploid cells as homologous chromosomes.
Homolog
A homolog refers to one member of a pair of homologous chromosomes.
Haploid (n)
Haploid cells carry one set of genetic information. i.e. possessing a single set of chromosomes (one genome).
- Gametes are haploid (n) in terms of chromosome number because these cells contain half the number of chromosomes as the respective somatic cells.
Diploid (2n)
Diploid calls carry two sets of genetic information; i.e. possessing two sets of chromosomes (two genomes).
- Human somatic cells (e.g., neurons, chondrocytes, white blood cells) are diploid and described 2n = 46.
Genome
Complete set of genetic instructions for any organism.
- All the genes present in a gamete are known as a genome.
C-value (c)
Amount of DNA per cell in an organism; the nu,ber of DNA molecules per cell equals the number of chromosomes when the chromosomes are unreplicated (no sister chromatids are present) and twice the number of chromosomes when sister chromatids are present.
- The measure of the amount of DNA in a genome is termed the C-value (c) and is expressed in units of mass or length (base pairs = bp).
Karyogram
Karyograms are the study of a whole set of chromosomes arranged in pairs by size and position of the centromere.
- A karyogram is an image that displays the chromosomes within a cell.
- The chromosomes used for a karyogram are specifically metaphase chromosomes and are customarily arranged by size and type.
- All chromosomes of the same size and with the same centromere position are sorted and grouped together with homologous chromosomes placed directly beside each other.
Cell Cycle
Stages through which a cell passes from one cell division to the next; the process by which cells alternate between a growth phase (interphase) and a dividing phase (mitosis and cytokinesis) to produce two new daughter cells.
Interphase (I)
Is the time during the cell cycle when cells perform designated functions, maintain structural and metabolic functions, and finally prepare to divide.
Is made up of three sub-phases/sub-stages:
- gap 1 (G1) phase,
- S-phase (S)
- Gap 2 (G2) phase
During G1 phase, the cell grows and carries out normal metabolic processes. During S phase, DNA replication occurs, in preparation for cell division. During G2 phase, the cell checks for DNA damage and makes final preparations for division.
Time spent in each stage can vary considerably between species and cell types.
- It is safe to assume that most cells spend the majority of time in interphase.
Gap 1 (G1) Phase
Stage of interphase in the cell cycle in which the cell grows and develops; begins when the previous round of cell division ends.
- Predominant G1 cellular functions include performing cell-specific duties and building new cellular components.
- DNA is not made during G1