meiosis 6.3 Flashcards
what is meant by diploid
- presence of two complete sets of chromosomes in an organism’s cells
- ^each parent contributing a chromosome to each pair
what are gametes
sex cells (sperm and eggs)
what is a zygote
The fertilised egg of an animal
what produces gametes
Gametes are formed by a form of cell division known as meiosis
What is the difference between meiosis and mitosis
- mitosis: produces 2 idential daughter cells, used for growth and repair
- meiosis: nucleus divides twice, produce 4 non-identical haploid gametes
What is meant by reduction division
Each gamete contains half of the chromosome number of the parent cell - it is haploid. Meiosis is therefore known as reduction division
what is meant by homologous chromosomes
- essentially identical but can contain different alleles
- have same gene sequence, loci, centromere location and chromosomal length
explain what is meant by an allele
Different versions of the same gene
what are the characteristics of genes on homologous chromosomes
- have same genes at same loci
^be same length and size when visible in prophase
what are the 2 main divisions of meiosis
meiosis I and meiosis II
what is another name for the first division that occurs in meiosis I and why has it got this name
- reduction division, pairs of homologous chromosomes are separated into 2 cells
- Each cell is haploid
explain what is produced at the end of meiosis II
The second division is similar to mitosis, and the pairs of chromatids present in each daughter cell are separated, forming 2 more cells.
4 haploid daughter cells are produced in total
what are the stages of Meiosis I
prophase I
Metaphase I
Anaphase I
Telophase I
what occurs in Prophase I
Chromosomes condense, the nuclear envelope disintegrates, the nucleolus disappears and spindle formation begins (as in prophase of mitosis)
what are bivalents
- set of two homologous chromosomes lying adjacent to each other held together at chiasmata