Applied Genetics (plant breeding) STB 421 Sixth lecture
What do mitosis and meiosis achieve?
A cell normally contain two of each type of chromosome, the diploid condition (2 large and two small chromosomes in the parent cells depeted in fig 1. above).
Mitosis preserves this condition, meiosis however resource in the daughter cells containing only one of each type of chromosome, the haploid condition.
MITOSIS
For purposes of description, mitosis is divided into four stages:i. Prophase
ii. Metaphase
iii. Anaphase and;
iv. Telophase
At each of this stages, certain crucial event take place particularly in regards to the chromosomes. However it is important to realize that mitosis is a continuos process and there are no sharp breaks between one stage and the next. Typically the entire process takes about an hour and is followed by a resting phase called Interphase, during which the daughter cells grow and prepare for the next division. This involves synthesis of new materials and replications of organelles. In actively dividing cells interphase last between 12 and 24 hours (see photocopy 1 on cell division).
MEIOSIS
We have seen that a built-in feature of meiosis is the preservation of the parental chromosome condition. In meiosis however, the number of chromosomes is halved, the daughter cells receiving only one of each type of chromosome instead of two.The daughter cells are said to be in the haploid state (haploid coming from the greek word haplous meaninh single).
Next topic will be on role of meiosis...