Meiosis Flashcards
Define:
-Haploid
-Diploid
-Chromatid
-Homologous pair
Haploid – Single set of unpaired chromosomes
Diploid - containing two complete sets of chromosomes, one from each parent.
Chromatid - each of the two thread-like strands into which a chromosome divides
Homologous pairs - A homologous chromosome is a set of one maternal chromosome and one paternal chromosome that pair up with each other inside a cell during meiosis.
Define:
-Crossing over
-Independent segregation
-Alleles
Cross-over - is the exchange of genetic material between homologous chromosomes
Independent segregation - formation of random combinations of chromosomes in meiosis
Alleles - same form of the same gene
What are Homologous chromosomes
What is a genetic loci
Pairs of chromosomes are known as HOMOLOGOUS CHROMOSOMES.
Each chromosome in a pair of chromosomes has the same length and shape and carries the same gene in the same location, or LOCUS.
Since each chromosome comes from one parent, the alleles for the same gene may be different (one
carrying B and one carrying b for blue eyes, for example)
A loci is the location of a particular gene on a chromosome. One on each homologous pair, one from each parent.
Define Meiosis
is a cell division process that results in the formation of 4 haploid gametes that are not genetically identical to the original parent cell.
what is the interphase?
What follows interphase?
Just as in mitosis, interphase must occur before meiosis. In interphase, the chromosomes must duplicate to create two chromatids each. Therefore, if we start with a 2n number of 4 chromosomes, we end up with 8 sister chromatids after replication.
Meiosis 1, where homologous pairs are separated,
Meiosis 2, where sister chromatids are separated,
What is in Meiosis 1 &2
Meiosis 1
Prophase 1
Metaphase 1
Anaphase 1
Telophase 1
Meiosis 2:
Metaphase 2
Anaphase 2
Telophase 2
Prophase 1 in detail:
what is the process and what can occur to improve genetic diversity
-Two chromatids condense and are joined by a central centromere
-pairs of homologous chromosomes match up with same genes aligning
-parts of non-sister chromatids may cross over.
Crossing over involves genetic material transferring between the lined up homologous chromosomes. This creates chromosomes that are known as ECOMBINANT
CHROMOSOMES. The location where the crossing over takes place is called CHIASMATA.
-spindle fibers form.
Metaphase 1 in detail:
The pairs of the homologous chromosomes align at the
metaphase plate, with each homologue orientated towards each pole. This orientation is random.
Spindle fibres then pull homologous chromosomes apart.
Anaphase 1 in detail:
1,the spindle fibres pull apart the homologous chromosomes towards the poles.
The combination of homologous chromosomes that gets pulled towards each pole is COMPLETELY RANDOM.
The cell membrane begins to close between the poles.
Telophase 1 in detail:
Two new cells are formed
Each of these cells is genetically unique because of the
random assortment of homologous chromosomes during anaphase 1 and also because of crossing over.
prophase 2 in detail:
During Prophase 2, the chromosomes again condense.
There is no interphase between the two stages of meiosis. Therefore, there is no replication of the DNA.
The spindle fibres begin to form in each of the newly formed haploid cells.
Metaphase 2 in detail:
The chromosomes are now aligned at the metaphase plate of each haploid cell.
The spindle fibres attach to the centromere of each sister chromatid
The arrangement of each chromosome along the metaphase plate is random, just as in Metaphase 1.
Anaphase 2 in detail:
The spindle fibres contract and thus pull the sister chromatids apart, towards each pole
Each cell membrane begins to constrict between the poles.
Telophase 2 in detail:
Four new cells are now formed. These cells are the gametes (sperm or ova)
Each of the haploid cells have different genetic material
(through recombination and random assortment of the
chromosomes).
How do these result in variation:
Crossing over
Independent assortment
Segregation
Because of crossing over, some of the gametes produced have a different combination of alleles on their chromosome(s) compared to the original parent chromosome(s). The allele combinations on a chromosome that are different to the original parent chromosome are called Recombinants
Each homologous pair of chromosomes line up randomly (with respect to other pairs) along the equator in meiosis (so the alleles of different genes that are carried on different chromosomes line up randomly in relation to each other). Independent assortment causes variation as it results in gametes with different allele combinations (between the different genes)
Segregation is when the homologous pairs of chromosomes separate from each other during Meiosis II so each gamete cell receives one copy of each gene (a single allele for each gene) Segregation causes variation because there is the possibility that it will result in gametes having a different allele for a gene; and that different allele combinations for a gene can be formed in fertilization through random gamete fusion
