Chapter 12 Flashcards
Meiosis
Asexual Reproduction
reproduction without sex
Gametes
sex cells
Female gamete
egg
male gamete
sperm
two gametes unite to form a single cell called a ______
zygote
The zygote is the first cell of _ ___ __________
a new individual
When a cell undergoes meiosis, ____ cells are produced from ___ successive divisions, which generally take place without pausing.
FOUR, TWO
When a cell undergoes meiosis, FOUR cells are produced from TWO successive divisions, which generally take place without pausing.
Prophase 1 in Meiosis
3 parts
- the chromosomes coil, becoming shorter and thicker; the chromosomes also become aligned in homologous pairs.
- the nuclear envelope and the nucleolus disassociate
- Parts of each closely associated pair of chromosomes are exchanged with each other.
Two homologous chromosomes paired at meiosis are called a ________
bivalent
centromere
a dense, constricted area of a chromosome to which spindle fibers become attached
spindle fibers
consist of microtubules that look like thin threads
Crossing over
results in an exchange of DNA contributed by the two parents, which is the basis for some of the variability seen in the offspring.
Chiasma (plural: chiasmata)
an “X” shaped figure that results from each cross over
Metaphase 1 of meiosis
2 parts
- The pairs of chromosomes become aligned at the equator of the cell
- The now complete spindle becomes more apparent
Anaphase 1 of meiosis
1 part
Each chromosome, consisting of two chromatids, migrates to a pole. the two chromosomes migrate to opposite poles
Telophase 1 of meiosis
This phase has been completed when the original cell has become 2 cells or 2 nuclei
Prophase II
Chromosomes become shorter and thicker, their two stranded nature once becomes more apparent
Metaphase II
- The centromeres of the chromosomes become aligned along the equator
- New spindles become conspicuous and complete
In metaphase II, the two spindles may be formed
either perpendicular to the ones that formed in Metaphase I or along the same plane
Anaphase II
The centromeres and chromatids of each chromosome separate and migrate to opposite poles
Telophase II (2 parts)
- the coils of the chromatids relax, so that the chromosomes become longer and thinner. At this point each chromosome consists of one DNA molecule in contrast to the two at the beginning of Meiosis II
- New nuclear envelopes and nucleoli appear for each group of chromosomes
Haploid
any cell having one set of chromosomes
Diploid
any cell with two sets of chromosomes
by the time meiosis is complete, ____ haploid cells have been produced by ___ diploid cell
FOUR, ONE
Triploid
cells that have three sets of chromosomes
Alternation of generations
occurs when a diploid SPOROPHYTE phase and a haploid GAMETOPHYTE phase
