Inheritance is the way in which parents pass on their characteristics to their offspring.
The study of inheritance is known as Genetics. (Parents pass on their genes to their offspring).
The Plant Cell (p 182, CXC Agriculture
The material of inheritance:
Inside nearly all cells there is a nucleus. The nucleus contains thread-like chromosomes. These
chromosomes carry the genes that control all the characteristics of an organism. Chromosomes
occur in pairs, but there are different numbers of chromosomes for different species of animals
and plants. (humans have 23 pairs, cats have 19 pairs, fruit flies have 4 pairs)
Each chromosome is made up of thousands of genes, it is the genes that carry the genetic
information that affects how we grow, what we look like, etc. If we unravel a chromosome, it
would form an extremely long thread. That thread is made up of a substance called DNA
(deoxyribonucleic acid).
New cells are made by cell division. Mitosis is a form of cell division. All cells are made by
mitosis except the sex cells. When a cell divides by mitosis it splits into 2 new daughter-cells.
These daughter cells are identical to the cell that they came from and to each other.
When does mitosis happen?
1. Mitosis occurs in growth. When living things grow they make new cells. Mitosis makes
these new cells whether it is in the growth of a baby or the germination of a seedling.
2. Mitosis occurs in asexual reproduction. The cells in the parent plant or animal divide to
make new cells which form the new individual.
Stages in mitosis:
Before a cell divide by mitosis it must make a second set of chromosomes.
Sex cells like sperm, eggs, pollen, ovules are made by a different kind of cell division. This cell
division is called meiosis. Meiosis halves the number of chromosomes. Eg. egg cells and sperm
cells only have 23 chromosomes each. The fertilized egg will have 46 chromosomes, 23 from
the mother in the egg, and 23 from the father, in the sperm.
Where does meiosis occur?
Meiosis occurs in the sex organs.
The ovaries make eggs by meiosis.
The testes make sperm by meiosis.
The anthers make pollen by meiosis.
The ovaries make egg cells by meiosis.
Stages in Meiosis: