Skills 7 & 8: Meiosis
Skill 7 - Explain how meiosis is a reduction division process and why reducing the number of chromosomes is necessary.
Skill 8 - Explain how sexual reproduction and crossing over contribute to genetic diversity. Why is this necessary?
It's story time. I'll read you, "The Date!" and you can choose how the story goes.
It's story time. I'll read you, "The Date!" and you can choose how the story goes.
Meiosis is the type of cell division which makes gametes, or sex cells, like sperm and egg. No other cells use this process for cell division.
Meiosis is the type of cell division which makes gametes, or sex cells, like sperm and egg. No other cells use this process for cell division.
Skill 7 - Explain how meiosis is a reduction division process and why that is necessary.
Skill 7 - Explain how meiosis is a reduction division process and why that is necessary.
Males make sperm cells and females make egg cells so that the two can join during sexual reproduction to form a new organism. Each gamete, sperm or egg, contains half of the chromosomes of a body cell. When you combine the half from the father (sperm) and the half from the mother (egg), you return to the normal number of chromosomes for the offspring, or baby. Gametes, or sex cells, are haploid, meaning they contain half the number of chromosomes of a body cell.
Males make sperm cells and females make egg cells so that the two can join during sexual reproduction to form a new organism. Each gamete, sperm or egg, contains half of the chromosomes of a body cell. When you combine the half from the father (sperm) and the half from the mother (egg), you return to the normal number of chromosomes for the offspring, or baby. Gametes, or sex cells, are haploid, meaning they contain half the number of chromosomes of a body cell.
Meiosis
Meiosis
Start with one diploid cell.
Start with one diploid cell.
Pair up chromosomes during prophase.
Pair up chromosomes during prophase.
Line up in the middle during metaphase.
Line up in the middle during metaphase.
Move them away during anaphase.
Move them away during anaphase.
Form two nuclei during telophase.
Form two nuclei during telophase.
The rest of the cell splits during cytokinesis.
The rest of the cell splits during cytokinesis.
Now one cell has divided into two. Do it again to make four cells.
Now one cell has divided into two. Do it again to make four cells.
Each of the four cells is different due to crossing over.
Each of the four cells is different due to crossing over.
Meiosis creates four different haploid cells.
Meiosis creates four different haploid cells.
Skill 8 - Explain how sexual reproduction and crossing over contribute to genetic diversity. Why is this necessary?
Skill 8 - Explain how sexual reproduction and crossing over contribute to genetic diversity. Why is this necessary?
Crossing over
Crossing over
of homologous pair
(a) Red = two copies of Mom's chromosome (chromatids)
(a) Red = two copies of Mom's chromosome (chromatids)
Green = two copies of Dad's chromosome (chromatids)
Green = two copies of Dad's chromosome (chromatids)
(b) One green chromatid crosses 'legs' with one red chromatid. They exchange a few genes.
(b) One green chromatid crosses 'legs' with one red chromatid. They exchange a few genes.
(c) Each of the four chromatids is now different, resulting in four different gametes.
(c) Each of the four chromatids is now different, resulting in four different gametes.
Crossing over demonstration - as a class
Crossing over demonstration - as a class
If you liked the video by Peter Weatherall on mitosis, here is one on meiosis you might like.
If you liked the video by Peter Weatherall on mitosis, here is one on meiosis you might like.
sWhat's the points of having meiosis when we already have mitosis?
sWhat's the points of having meiosis when we already have mitosis?
Meiosis produces haploid cells, those with half the usual number of chromosomes. This is important because, in sexual reproduction, the offspring receive half of their chromosomes from their mother and the other half from their father. When you combine the two halves, the baby has the right number of chromosomes again.
Meiosis produces haploid cells, those with half the usual number of chromosomes. This is important because, in sexual reproduction, the offspring receive half of their chromosomes from their mother and the other half from their father. When you combine the two halves, the baby has the right number of chromosomes again.
It is also important that sex cells are different. This is why you may share traits with your brothers and sisters, but you are not exactly the same. You only received half of your traits from your father and the rest from your mother. If all humans were genetically identical, we would all be susceptible to the same diseases and we would not have survival of the fittest, which helps the species evolve and survive over time.
It is also important that sex cells are different. This is why you may share traits with your brothers and sisters, but you are not exactly the same. You only received half of your traits from your father and the rest from your mother. If all humans were genetically identical, we would all be susceptible to the same diseases and we would not have survival of the fittest, which helps the species evolve and survive over time.
Genetically diverse populations are more likely to survive changing environments. Recombination of genes caused by sexual reproduction and crossing over, as well as mutations, provides for genetic diversity. Some new gene combinations have little effect, some can produce organisms that are better suited to their environments, and others can be detrimental, or negative.
Genetically diverse populations are more likely to survive changing environments. Recombination of genes caused by sexual reproduction and crossing over, as well as mutations, provides for genetic diversity. Some new gene combinations have little effect, some can produce organisms that are better suited to their environments, and others can be detrimental, or negative.