Chapter 10.1: Meiosis Flashcards
What are the 6 things that happen during prophase I?
The chromosomes condense and become visible and centrioles
duplicate. The homologous will chromosomes pair up, forming
bivalents. Chiasmata, where crossing over has occurred, become
visible. The centrioles move to the poles of the cell and the nuclear
membrane begins to break down
What are the 4 things that happen during Metaphase I?
The chromosomes become shorter and thicker and the spindle
microtubules attach to the centromeres. The bivalents lines up along the
equator. Those with chiasmata temporarily have unusual shapes. The
spindles attach to the chromosomes and start to pull them apart.
What are the two things that happen during Anaphase I?
The spindle fibres begin to shorten, separating the homologous
chromosomes. They are pulled to opposites poles, thereby halving
the chromosome number. Each of the chromosomes is made up of
two chromatids; however, these might not be identical due to
crossing over
What are the 3 things that happen during Telophase I?
The nuclear membranes begin to reform around the chromosomes. The
cell membrane closes, dividing into two cells. The chromosomes begin
to uncoil partially. The new cells may enter a short interphase, but
there will be no further replication of the DNA.
What are the three things that happen during Prophase II?
The chromosomes recoil, becoming short and thick once
again. The centrioles replicate and move to opposite poles.
The nuclear membranes will break down.
What are the 3 things that happen during Metaphase II?
The spindle fibres begin to form and attach to the
chromosomes by the centromere. The chromosomes line up
along the equator. The centromeres divide to allow the
chromosomes to separate.
What happens during Anaphase II?
The sister chromatids are separated, pulled apart by the
spindle fibres to the opposite poles.
What are the 3 things that happen during Telophase II?
The chromatids decondense and are now known as chromosomes.
The nuclear membrane and nucleoli reform around the DNA. The
cells divide, forming a total of four haploid cells.
-Outline formation of chiasmata in the process of crossing over
Breakages of the chromatids occur frequently during the
coiling and shortening process, but this is immediately
repaired. However, since the homologous chromosomes
are paired closely together, these fragments may swap
between non-sister chromatids. The place where the
crossing over occurs is called the chiasma (plural:
chiasmata). This results in new combinations of genes.
How does crossing over contribute to genetic variety?
This is when fragments of DNA are swapped between homologous chromosomes, forming
new combinations of linked genes. The new genotypes are not due to random assortment.
There are virtually unlimited possibilities of recombinations.
When does crossing over occur?
prophase I
How does random orientation contribute to genetic variety?
During metaphase I, the bivalents line up randomly along the equator. The homologous pairs
and their alleles are separated. However, the chromosomes move independently of each
other, so there is no relationship between the chromosome and which pole it moves to. A
total of 2^23 combinations can be formed in humans.
When does random orientation occur?
metaphase I
State Mendel’s law of independent assortment
Allele pairs separate independently during the formation of gametes. If two genes are
unlinked, then the pairs of alleles will be segregated randomly during meiosis. As a result,
traits are transmitted to offspring independently of one another
Explain the relationship between Mendel’s law of independent assortment and
meiosis
Independent assortment is the result of random orientation of the homologous
chromosomes during metaphase I. Mendel’s discoveries were based on physical
characteristics, or phenotypes, and not the actual alleles or chromosomes.
