Chapter 19 Flashcards
Chromatin
DNA that has been packaged with protein
Chromosome
Condensed chromatin
Sister chromatid
After a chromosome copies itself, the chromosome has two sister chromatids, so each copy is called a sister chromatid.
Centromere
A protein-based structure that holds together the two sister chromatids
Duplicated chromosome
Sister chromatids that contain the same genes
Unduplicated chromosome
Homologous chromosome
A pair of chromosomes that look alike and carry genes for the same traits.
Diploid
Two sets of chromosomes
Haploid
One set of chromosomes
Gene vs. Allele
Gene: What it codes for
Example: Eye color
Allele: Specific variety
Example: Blue eyes, brown eyes, green eyes
How many chromosomes
In the human cell
In gametes
Human cell: 46
Gametes: 23
Autosomes vs sex chromosomes
Autosomes: The chromosomes that are found in both males and females
How many: Twenty-two
Sex chromosomes: The chromosome that controls gender. Males have XY and females XX
How many: One
Interphase
The time when the organelles in the cell carry on their usual functions.
Three main phases
G1 phase: Cell returns to normal size and resumes its function in the body. A cell doubles its organelles, and it accumulates the materials needed for DNA synthesis
S phase: A copy is made of all the DNA in the cell. DNA replication occurs, so each chromosome consists of two identical DNA double-helix molecules. The molecules occur in the strands called sister chromatids
G2 phase: The cell synthesizes the proteins needed for cell division, such as the protein found in microtubules.
Mitosis
The cells that go under mitosis are all of the cells except neurons, white blood cells, and skeletal muscle cells.
Four main phases
Prophase: The centrosomes outside the nucleus have duplicated, and they begin moving away from one another toward opposite ends of the nucleus. Spindle fibers appear between the separating centrosomes. The nuclear envelope begins to fragment. The nucleolus disappears as the chromosomes coil and become condensed. The chromosomes are now clearly visible. Each is composed of two sister chromatids held together at a centromere.
Metaphase: The spindle is fully formed. The metaphase plate is a plane perpendicular to the axis of the spindle and equidistant from the poles. The chromosomes, attached to spindle fibers at their centromeres, line up at the metaphase plate during metaphase.
Anaphase: The centromere uniting the sister chromatids divide, then the sister chromatids separate, becoming chromosomes that move toward opposite poles of the spindle.
Telophase: The chromosomes arrive at the poles. During telophase, the chromosomes become indistinct chromatin again. The spindle disappears as the nuclear envelope components reassemble in each cell.
In the end, you are left with four daughter cells
Meiosis
Gametes go under meiosis
Two divisions
Eight phases
Prophase I: Homologous chromosomes pair during synapsis allowing for crossing-over to occur
Metaphase I: Independent assortment occurs as homologous chromosomes pair along the metaphase plate
Anaphase I: Homologous chromosomes separate, pulled to opposite pols by centromeric spindle fibers
Telophase I: Daughter cells have one chromosome from each homologous pair
Prophase II: Cells have one chromosome from each homologous pair
Metaphase II: Chromosomes align at the metaphase plate
Anaphase II: Daughter chromosomes move toward the poles
Telophase II: Spindle disappears, nuclei from, and cytokinesis takes place
In the end, you are left with four daughter cells
Why are haploid produced during meiosis
Haploids are produced during meiosis because you need half the cells.
This is necessary for fertilization
Major differences between mitosis and meiosis
Mitosis is the duplication division, while meiosis is the reduction division
Crossing over
Homologous chromosomes find each other, and swap DNA
Advantage: Genetic variation
Independent assortment
Gametes have a random assortment of chromosomes; some from mom, and some from dad
Advantage: Genetic variation
Karyotype
A way of viewing an unborn child’s chromosomes to determine whether a chromosomal abnormality exists.
Aneuploidy
Having either not enough, or too many chromosomes
Nondisjunction
The failure of the homologous chromosomes or daughter chromosomes to separate correctly during meiosis I and meiosis II
Monosomy
When an egg with 22 chromosomes is fertilized with normal sperm
Examples: Couldn’t find
Trisomy
When an egg with 24 chromosomes is fertilized with normal sperm
Examples: Down syndrome
Four types of changes in chromosome structure that can occur
Deletion: When an end of a chromosome breaks off, or when two simultaneous breaks lead to the loss of an internal segment.
Duplication: The presence of a chromosomal segment more than once in the same chromosome.
Inversion: When a segment of a chromosome is turned around 180°.
Translocation: The movement of a chromosome segment from one chromosome to another nonhomologous chromosome.
