Life sciences grade 12

Meiosis is the type of cell division used to produce gametes or s*x cells (s***m and egg cells). A cell undergoing meiosis will divide twice.

– the first division is meiosis I and the second is meiosis II.

In the first meiotic division, the number of cells is doubled, but the number of chromosomes is not.

This results in half as many chromosomes per cell.

In the second meiotic division, the number of chromosomes does not get reduced.

Abnormal meiosis

• Sometimes mistakes occur during the process of meiosis.

• This can happen in Anaphase 1 where the homologous chromosomes may not separate. Also called non-disjunction.

• It can also happen in Anaphase 2 when there is non-disjunction of the sister chromatids.

• If there is non-disjunction of chromosome pair 21 in humans, it leads to the formation of an abnormal gamete with an extra copy of chromosome 21.

• If there is fusion between a normal gamete and an abnormal gamete (with extra copy of chromosome 21) it leads to Down Syndrome.

The significance of meiosis

There are two reasons why meiosis is important.

1. It reduces the number of chromosomes by half, in other words from diploid to haploid. This ensures that s*x cells have half the number of chromosomes of other somatic cells so that when fertilisation occurs the zygote formed has the correct number of chromosomes. It balances the doubling effect of fertilisation.

2. Crossing over introduces genetic variation. Genetic variation results in offspring that are better adapted to a particular environment and ensures that they will have a better chance of survival.

*Mitosis:* It's like a cell's way of cloning itself. One cell divides into two identical cells. Phases are prophase, metaphase, anaphase, telophase, and cytokinesis. Used for growth, repair, and replacement of cells.

*Meiosis:* This one's for reproduction. One cell divides into four non-identical cells (gametes - s***m or egg). Two rounds of division (meiosis I & II). Results in genetic variation.

For mitosis:
- Prophase: Chromatin condenses, nuclear envelope breaks down
- Metaphase: Chromosomes line up at the center
- Anaphase: Sister chromatids separate
- Telophase: Nuclear envelope reforms
- Cytokinesis: Cell splits into two

For meiosis:
- Meiosis I: Homologous chromosomes separate (reduces chromosome number by half)
- Meiosis II: Sister chromatids separate (like mitosis)

*Mitosis example:* Human skin cells regenerate through mitosis, replacing old skin with new ones.

*Meiosis example:* In humans, meiosis produces s***m (males) and eggs (females), contributing to genetic diversity in offspring.

DNA: The Code Of Life.

For South African Grade 12 Life Sciences, there has not been a major change to the exam structure for 2026. The Department of Basic Education is still using the examination guidelines introduced in 2021 while revised guidelines are being reviewed for future implementation. �
Ecexams
The current structure remains:
Paper 1: 150 marks, 2½ hours
Human Reproduction
Reproduction in Vertebrates
Responding to the Environment (Humans and Plants)
Endocrine System
Homeostasis
Paper 2: 150 marks, 2½ hours
DNA and Genetics
Meiosis
Inheritance
Evolution �
StudyClix +1
What has changed in recent years is that examiners may use more data-based questions, interpretation of diagrams, investigations, and application-type questions rather than simple recall. However, the two-paper format and mark allocation remain the same. �
Studocu +1

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Evolution is not something you “believe in.”

It is one of the most tested, observed, and supported frameworks in all of science.

In everyday language, “theory” can sound like a guess. But in science, a theory is much stronger: it is an explanation that ties together a vast amount of evidence and makes predictions that can be tested.

Evolution does exactly that.

It explains why bacteria can become resistant to antibiotics. It explains why viruses keep changing. It helps scientists track disease outbreaks, improve crops, protect endangered species, and understand how every living thing on Earth is connected.

The evidence comes from many directions.

The fossil record shows life changing over time in a consistent order. Fish appear before amphibians. Reptiles appear before mammals. Transitional fossils help fill in major evolutionary steps, from Tiktaalik, a fish-like animal with limb-like bones, to early whales with traits linking them to land mammals.

Anatomy tells the same story. The forelimbs of humans, bats, cats, and whales look very different on the outside, but inside they share the same basic bone pattern. That is not random. It is a signature of common ancestry, reshaped over millions of years for walking, flying, swimming, and grasping.

DNA makes the case even stronger.

All life uses the same basic genetic code. Humans share more than 98% of their DNA with chimpanzees and about 60% with fruit flies. Those similarities are not just interesting facts. They are evidence that life on Earth is related through descent.

And evolution is not only something we infer from ancient fossils. We can watch it happen.

Scientists have seen bacteria evolve drug resistance, viruses accumulate new mutations, and animals adapt to new environments over just a few generations. Evolution is happening in hospitals, farms, forests, oceans, and inside our own bodies.

Darwin helped explain one major mechanism: natural selection. But modern evolutionary biology goes much further, including genetics, genetic drift, coevolution, molecular evolution, and more.

Evolution is the thread connecting every fossil, every gene, every species, and every living thing on Earth.

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