Summary Life sciences (Biology) - Chromosomes and meiosis.

CHROMOSOMES AND MEIOSIS:
HAPLOID VS DIPLOID:
 Diploid cells (2N)
- Have two complete sets of chromosomes
- Animal body cells are diploid

 Haploid cell (N)
- Have one complete set of chromosomes
- Animal gametes ( sperm and egg cells) are haploid



HOMOLOGOUS CHROMOSOMES:
 Diploid organisms have two copies of each chromosome ( except sex
chromosomes)
 Each pair of chromosomes is homologous




 One maternal chromosome and one paternal chromosome
 The two chromatids are identical for each chromosomes
 Two chromatids are joined at the centre by a centromere to form a chromosome


WHY DO CELLS NEED TO DIVIDE:
 Single-celled organisms divide to reproduce
 Multicellular organisms cell division allows the organism to grow
 Some multicellular organisms must divide to produce sex cells

, CELL CYCLE:


2N


(Meiosis)

Egg cells Sperm cells
(N) (N)



(Fertilisation)




Zygote

(2N)




MITOSIS VS MEIOSIS:

Meiosis Mitosis
Homologous chromosomes pair up at single chromosomes line up at the
equator equator

Crossing over No crossing over

Two cell divisions One cell division

Four unidentical daughter cells Two identical daughter cells

Haploid daughter cells Diploid daughter cells