Cell division and stem cells Flashcards
Where are chromosomes found?
In the nucleus of every cell.
When are chromosomes visible?
Only when the cell is about to divide.
What are chromosomes made out of?
DNA (deoxyribonucleic acid)
What are genes?
Genes are sections of DNA that control the features of an organism.
How many chromosomes are there in humans?
46 chromosomes (23 pairs, 23 from each parent).
Are the pairs in meiosis identical?
They are not identical because the form of the gene (called an allele) can vary.
What are xy and xx chromosomes?
Male and female.
What are the sex determining chromosomes?
Pair number 23.
What does cell division result in?
In multicellular organisms, it results in growth, repair, replacement of old or damaged cells and tissues.
What is mitosis?
Where one cell (the mother cell) divides to form 2 new (daughter) cells. The daughter cells are genetically identical to the mother cell because the chromosomes replicate themselves and one copy is passed into each of the new 2 cells.
In mitosis, is the number of chromosomes in the mother and daughter cells the same?
Yes, both have equal chromosomes.
When does meiosis occur?
It only occurs when sex cells (gametes) are formed.
What is meiosis?
Although the DNA and chromosomes duplicate like mitosis, 4 new cells are formed instead of 2, and each cell receives half a set of chromosomes. (23 each)
Do the pairs of cells in meiosis form identically?
The chromosomes have pairs that are not identical because during the process meiosis the gametes get one chromosome from each pair. The new cells in meiosis are therefore not identical.
Why is mitosis carefully regulated?
Mitosis is carefully regulated to allow time for cells to grow and become specialised. Sometimes this control fails, mitosis gets out of control and the cells produce cancerous tumours.
What are the 4 main points regarding mitosis?
- Occurs in all body cells except those forming gametes.
- Daughter cells are genetically identical.
- 2 daughter cells are formed.
- Daughter cells have a full set of chromosomes.
What are the 4 main points regarding meiosis?
- Occurs only in gamete-forming cells.
- Daughter cells are genetically different.
- 4 daughter cells are formed.
- Daughter cells have half sets of chromosomes.
What is an embryo?
Undifferentiated clumps of cells that have not yet specialised. The can turn into any cell.
What happens when a cell differentiates?
They can only form cells similar to themselves.
What are stem cells?
The undifferentiated cells in the embryo.
What can stem cells do?
Grow them into different types of cell that can be used to repair or replace damaged tissue.
What are the advantages to stem cell therapy?
- They could be used to treat diseases such as cancer and type 1 diabetes, which affect or kill millions of people.
- They can be used to repair damaged damaged tissue, such as brain damage or spinal cord injuries which can result in paralysis.
What are the objections to stem cell therapy?
- Any embryo has the potential to develop into a human being, and so the process destroys life. However, the embryos used are those rejected during fertility treatment, so even if they were not used they would never get the chance to develop.
- Some people are worried that embryos might be created specifically to produce stem cells, so it would be like ‘farming’ human beings (but this is not a current issue, rather one to consider in the future).
What are alternatives to stem cell therapy?
- Stem cells can be found in adults (bone marrow). These cells are in mature tissues but have not lost the ability to differentiate into different cells. The issue is they cannot develop into as many types of cells as embryos can.
- Stem cells can be collected from the umbilical cord at birth. These could be useful in treating that same baby later in life as the cells would be genetically identical to its own cells and so would not be attacked by its own immune system.
