REPRODUCTION AT THE CELLULAR LEVEL Flashcards
Autosomes
are the 22 pairs of chromosomes that control traits unrelated to gender.
Sex chromosomes
are the 1 pair that contains the genes that do control gender.
diploid
(body cells) that have 46 (2n) paired chromosomes are called
haploid
(sex cells) that have only 23 (n) unpaired chromosomes are called
The cell cycle 5
Interphase
– cell doubles its organelles; cell grows
in size
– DNA replication occurs
– proteins needed for division are synthesized
– nuclear division Cytokinesis
– cytoplasmic division
major checkpoints 3
G1, if passed, the cell is committed to divide.
G2 cycle pauses to verify DNA replication.
M cycle pauses to verify spindle assembly and chromosome attachment.
Chromosomes that are dividing are made up of two identical parts called__________
sister chromatids.
centromere
where the sister chromatids are held together at a region
Mitosis occurs in body cells.
There are four phases.
Prophase Metaphase Anaphase Telophase
PROPHASE
1 Chromosomes condense and become visible. The nuclear envelope fragments. The nucleolus disappears. Centrosomes move to opposite poles. Spindle fibers appear and attach to the centromeres.
MITOSIS: METAPHASE
2
Chromosomes line up at the middle of the cell (equator).
Spindle becomes fully-formed.
MITOSIS: ANAPHASE
3
Sister chromatids separate at the centromeres and move towards the poles.
MITOSIS: TELOPHASE AND CYTOKINESIS
4
Chromosomes arrive at the poles.
Chromosomes become indistinct chromatin again.
Nucleoli reappear.
Spindle disappears.
Nuclear envelope reassembles.
Two daughter cells are formed by a ring of actin filaments (cleavage furrow).
Meiosis occurs
in sex cells
Prophase I
1
Homologous chromosomes pair (synapsis); crossing- over occurs, in which there is exchange of genetic information.
Metaphase I
2
Homologous pairs line up at the equator.
Anaphase I
3
Homologous chromosomes separate and move toward opposite poles
Telophase I
4
Two daughter cells result, each with 23 duplicated chromosomes.
Prophase II
5
Chromosomes condense again.
Metaphase II
6
Chromosomes align at the equator.
Anaphase II
7
Sister chromatids separate to opposite poles.
Telophase II
8
Four daughter cells result, each with 23 unduplicated chromosomes.
MITOSIS VS. MEIOSIS differences
MITOSIS
Growth and repair of cells Occurs in body cells
1 division
Results in 2 diploid, genetically identical cells
MEIOSIS
Formation of gametes Occurs in sex cells
2 divisions
Results in 4 haploid, genetically different cells
Monosomy
cell has only 1 copy of a chromosome e.g., Turner syndrome (only 1 X chromosome)
Trisomy
cell has 3 copies of a chromosome
e.g., Down syndrome (3 copies of chromosome 21)
