chapter 2.7 meiotic division (meiosis) Flashcards
Diploid cells contain pairs of homologous chromosomes. Recognise, describe, and represent the process of meiosis in eukaryotic cells. Explain why the products of meiosis are haploid cells and contain a single set of chromosomes. Explain the importance of crossing over and independent assortment in meiosis. Explain that fertilization restores the diploid number. Compare the products of meiotic and mitotic cell division. Compare the sources and degree of genetic variation between the products
What is a homogulous chromosome?
A pair of homologous chromosomes, or homologs, is a set of one maternal and one paternal chromosome that pair up with each other inside a cell during fertilization
What are haploid cells?
Haploid cells are cells which contain one/ a singular set of chromosomes(1 chromatid).
What are diploid cells?
Diploid cells are cells which contain pairs of homologous chromosomes.
What is Meiosis?
Meiosis:
- Reduction cell division (diploid 🡪 haploid)
- Occurs in the germ cells of the testes and ovaries
- Produces the sex cells – called gametes or germline cells (sperm and egg)
- Occurs in two parts
*Essentially the main purpose of meiosis is to produce sperm cells in males and egg cells in females which are haploid cells; having only one member of each homologuous pair. *
How many rounds of PMAT does Meiosis go through?
It goes through 2:
Round 1:
Prophase 1
Metaphase 1
Anaphase 1
Telaphase 1
Round 2:
Prophase 2
Metaphase 2
Anaphase 2
Telaphase 2
What occurs in Prophase 1?
- chromosomes condense and thicken
- homologous chromosomes pair up forming a bivalent (connected)
- crossing over occurs (chromosomes transfer genetic infromation, exchanging between each other making recombinant chromosomes)
- nuclear membrane breaks down, disappearing.
What occurs in Metaphase 1?
- the pairs of the homologous chromosomes (bivalents) line up to the middle (equator) of the cell.
What occurs in Anaphase 1?
-the homologous pairs have been randomly arranged at the equator
- now they are seperated or assorted independently, where one chromosome of each pair goes to each pole of the cell.
What occurs during telophase 1?
- chromosomes arrive at the poles of the cell
- new nuclei forms
- spindle fibre breaks down and disappears
- cytokinesis occurs, and two cells are formed
Whats happens in Prophase 2?
- new spindle is formed, but no replication has occured this time
What happens during Metaphase 2?
- the chromosomes, each consistings of two identical sister chromatid, attach to the spindle fibres in the middle (or at the equator).
What happens during Anaphase 2?
The sister chromatids of each chromosomes are seperated and move to opposite poles.
What happens during telaphase 2?
- spindle fbires disappear
- nuclear membrane re-forms
- nucleolus becomes visible
- cytokinesis occurs
essentially left with four haploid cells.
What are sources of genetic variation in Meiosis?
The main sources of variation include:
- crossing over during prophase 1
- independent assortment during anaphase 1
- fertilisation which restores the diploid number when a sperm and its unique genetic profile fuses with an ovum.
How does crossing over lead to genetic variation?
When homologous chromosomes come together to form bivalents, the arms of the chromatids can swap at random, creating many more possibilities for genetic variation of the gametes.
