Topic 4: Genetic variation: meiosis Flashcards
(21 cards)
What is meiosis?
The nuclear division that results in 4 genetically different daughter cells, that have half the DNA of the parent cell.
How can you tell if a cell went through meiosis?
Meiosis involves going from a diploid cell (2n) parent cell to a haploid cell (n).
What is the main role of meiosis?
The production of haploid gametes, for sexual reproduction.
How is genetic variation achieved through meiosis?
-Independent segregation of homologous chromosomes
-Crossing over of homologous chromosomes.
What is independent segregation?
The random separation of homologous chromosome pairs leading to genetic variation in gametes.
What is the crossing over of homologous chromosomes?
The exchange of genetic material between homologous chromosomes, creating new combinations of alleles and increasing genetic variation.
How does independent segregation achieve genetic variation?
-Homologous pairs of chromosomes line up opposite each other at the equator.
-It’s random which side of the equator the paternal and maternal chromosomes will line up.
How does crossing over of homologous pairs create genetic variation?
-Homologous pairs of chromosomes line up opposite each other at the equator.
-Parts of the chromatid become twisted around each other, creating tension on the chromatid.
-Causes parts of the chromatid to snap and break off.
- They then recombine on the other chromosome of the pair, forming a new combination of alleles.
What do you call the part where the chromatids are twisted over each other?
Chiasma or Chiasmata
What do you call the end product after the chromosomes have exchanged their alleles?
Bivalent
What are homologous chromosomes?
Pairs of chromosomes with the same gene at the same loci
What’s the difference between mitosis and meiosis?
- Mitosis results in 2 identical daughter cells, each with the same number of chromosomes as the parent cell.
- Meiosis results in 4 genetically different daughter cells, each with half the number of chromosomes.
What’s the main difference of meiosis I and meiosis II ?
- Meiosis I: Homologous chromosomes are separated
- Meiosis II: Chromatids are separated
What happens during Prophase 1?
-Chromosomes condense
-Nuclear envelope disintegrates
-Spindle fibres begin to form
- Homologous chromosomes pair up
- Crossing over occurs
What happens during metaphase 1?
-Chromosomes align on the cell equator
- Spindle fibres attach to the kinetochore on centromere
-Independent segregation occurs
What happens during anaphase 1?
-Homologous pairs of chromosomes are separated as microtubules pull whole chromosomes to opposite ends of the spindle
What happens during telophase 1?
-Chromosomes at the opposite poles
-Spindle fibres start to break down
-Nuclear envelope forms around 2 groups of chromosomes and nuclei reforms
-Chromosomes uncoils.
What is non-disfunction?
Occurs when the sister chromatids don’t separate properly during meiosis, leading to uneven distribution of chromosomes.
What are the 2 types of chromosome mutations?
-Polyploidy
-Aneuploidy
What is polyploidy?
Changes in the whole set of chromosomes
What is aneuploidy?
Changes in the number of individual chromosomes so a cell might have 1 extra, or less chromosome.
