Meiosis Flashcards
Describe meiosis
Nuclear division
Haploid gametes from diploid cells
Daughter cell half the number of chromosomes than parent cell
Two haploid gametes fuse - diploid zygote
Prophase 1
The nuclear membrane breaks down
DNA condenses and becomes visible as chromosomes
DNA replication has already occurred so each chromosome consists of two sister chromatids joined together by a centromere
The chromosomes are arranged side by side in homologous pairs
As the homologous chromosomes are very close together the crossing over (genetic recombination)
of non-sister chromatids may occur
Spindle fibers form
Metaphse 1
Paris of Hc line up at equator Of spindle
SF attach to centromere
The maternal and paternal chromosomes in each pair position themselves independently of the others;
this is independent assortment
This means that the proportion of paternal or maternal chromosomes that end up on each side of
the equator is due to chance
Anapahse 1
HC pairs seperated - microtubupes pull whole chrom to opp ends of spindle
Telephase 1
Chrom arrive at opp poles
SF start to breakdown
Nuclear envelope form around two groups of chrom and nucleoli reform
Cytokinesis
Division of cytoplasm
Cell organelles disturbuted
2 haploid crlls
Cytokinesis
Division of cytoplasm
Cell organelles disturbuted
2 haploid cells
P 2
Nuclear envelope breaks down
Chrom condense visible
M 2
Chrom line up in single file along equator of spindle
A 2
Sis chrom pulled to opp piles of cell
This creates four groups of chromosomes that have half the number of chromosomes compared to
the original parent cell
Telophase 2
Nuclear membrane forms around each group of chrimsokes
Cytokinesis 2
Cytoplasm divides as new cell surface membranes are formed creating four haploid cells
Comparing mitosis and meiosis
Mitosis and meiosis are
both processes of cell division that result in chromosome segregation
Mitosis supports an organism
’s growth and replaces damaged or dying cells by producing wo
daughter cells genetically identical to each other and the parent cell
This consistency allows for continuous growth and tissue maintenance in all
body cells (except
gametes)
In contrast, meiosis generates genetically different gametes for sexual reproduction
Meiosis creates four daughter cells all of which contain half the genetic material of the parent cell
and are all unique from each other and the parent
This variation is essential for genetic diversity within families and populations, reducing the
likelihood of inheriting genetic disorders
Crossing over
Non sis chrom exchange alleles
In meiosis 1
Hc pair up close to eachother
Sections of DNA from non-sister chromatids can cross over and get entangled
3. These crossing points are called chiasmata
4. A section of chromatid from one chromosome may break and rejoin with the chromatid from theother chromosome
Independent assortment
P1 Hc pair up, M1 pulled towards equator of spindle
Random - each pair can be arranged with either chrom on top
Random fertilisation
Each gamete carries substantially different alleles
During fertilization, any male gamete can fuse with any female gamete to form a zygote
This random fusion of gametes at fertilization creates genetic variation between zygotes as each will have a unique combination of alleles
The presence of genetically diverse zygotes contri
butes to the genetic diversity of a species
