Meiosis

Jamie Z 2024-11-05

Learning Goals

• Describe the process of meiosis
• Compare the process and role of mitosis and meiosis
• Explain how random assortment during meiosis leads to genetic diversity

Mitosis VS Meiosis

Mitosis	Meiosis
Role: For growth and development, repair and asexual reproduction	Role: For sexual reproduction to produce gametes
Only one phase (IPMAT)	Two phases (IPMAPMAT)
Results in 2 diploid daughter cells with identical genetic information to parent cell	Final product is 4 unique haploid daughter cells
Result for humans: Two daughter cells with 46 chromosomes in each	Result for humans: Four daughter cells with 23 chromosomes in each

Role of Meiosis

• The process of meiosis is responsible for the production of the sex cells, also known as gametes
• Gametes are produced by cells in reproductive organs
• Gametes contain half the chromosomes (haploid)
• This is important for sexual reproduction to form a zygote, there is a whole set of genetic information (not double)

Meiosis IPMAT-PMAT

• Meiosis results in 4 genetically different daughter cells
• An additional “crossing over” step, which is not present in mitosis results in genetic variance
• Once fertilisation occurs, the zygote contains full number of chromosomes
• Genetically unique gametes produce unique offspring, ensuring genetic variation within species

Interphase

• Interphase progresses the same as mitosis
• Genetic information is duplicated - for humans there are 92 chromatids
• There are still 46 “chromosomes” because we count by centromeres

The first phase

Prophase I

• The nucleus breaks down, chromosomes are are condensed. Spindle fibres being to appear
• Crossing over occurs, lining up chromosomes in homologous pairs and share information
• This where it differs from mitosis, because it causes genetic variation

Metaphase I

• Chromosomes line up in the middle. They are still in pairs

Anaphase I

• Chromosomes are pulled apart to opposite ends, separating them opposite ends of the cells

Telophase / Cytokinesis I

• The parent cell divides to produce two new cells. Each new cell contains one duplicated chromosome from each pair. This means that the cells are haploid. They contain half the number of chromosomes found in the parent cell.

The second phase

• At the start of the second round of PMAT, the ‘parent cell’ is haploid (not containing double the genetic info) and therefore, at the end of telophase II and cytokinesis II four HAPLOID daughter cells are produced. These are each GENETICALLY DIFFERENT due to the crossing over that occurred in prophase I.

Prophase II

• The chromosomes condense, and a new set of spindle fibres forms.

Metaphase II

• In each of the two cells produced by the first round of cell division, the chromosomes align in the centre of the cell.

Anaphase II

• Each duplicated chromosome is pulled apart to opposite ends of the cell.

Telophase / Cytokinesis II

• Both cells divide in two. This produces four daughter cells in total. Each daughter cell is a separate gamete.
• The daughter cells are all haploid, and contain a genetically different set of chromosomes.