MEIOSIS

The significance of meiosis

MeiosisCell division that is vital for sexual reproductionTakes place in reproductive organsResults in formation of haploid gametesThe four daughter cells are not genetically identical

Meiosis and genetic variation

There are two main ways in which genetic

variation occurs at meiosis:

1. Random segregation of chromosomes

2. Crossing over

Meiosis and genetic variation

Random segregationDuring metaphase 1 homologous chromosomes arrive at the equatorThey arrange themselves in a random order on the equator

Meiosis and genetic variation

Random segregationIn a cell with just two pairs of chromosomes there are four different types of outcomes for the way the chromosomes can separate.

Meiosis and genetic variation

Random segregationIn human cells with 23 chromosomes there are 223 different possible ways the chromosomes can segregate!That is over 8 000 000 different types of gamete

Meiosis and genetic variation

During fertilization any male gamete can join with any female gametes.So thousands of millions of new genetic combinations are possible.

Meiosis and genetic variation

Crossing overDuring prophase 1 of meiosis homologous chromosomes come together in pairs

Meiosis and genetic variation

Crossing overEach chromosome is divided into two chromatidsThe homologous chromosomes twist around each otherThis creates tension, which may cause breaks to occur along the length of the chromatids

Meiosis and genetic variation

Crossing overDuring cross over, corresponding fragments may get swapped over.This “cutting and sticking” means that genetic material is exchanged.This creates new genetic combinations and variation in the gametes is increased.

Differences between mitosis and meiosis

Mitosis Meiosisone division

Differences between mitosis and meiosis

Mitosis Meiosisone division two divisions

Differences between mitosis and meiosis

Mitosis Meiosisone division two divisions

the number of chromosomesremains the same

Differences between mitosis and meiosis

Mitosis Meiosisone division two divisionsthe number of chromosomes the number ofremains the same chromosomes is

halved

Differences between mitosis and meiosis

Mitosis Meiosisone division two divisionsthe number of chromosomes the number ofremains the same chromosomes is

halvedhomologous chromosomesdo not pair up

Differences between mitosis and meiosis

Mitosis Meiosisone division two divisionsthe number of chromosomes the number ofremains the same chromosomes is halvedhomologous chromosomes homologous

chromosomesdo not pair up pair up to form bivalents

Differences between mitosis and meiosis

Mitosis Meiosisone division two divisionsthe number of chromosomes the number ofremains the same chromosomes is halvedhomologous chromosomes homologous

chromosomesdo not pair up pair up to form bivalentschiasmata do not form andcross over never occurs

Differences between mitosis and meiosis

Mitosis Meiosisone division two divisionsthe number of chromosomes the number ofremains the same chromosomes is halvedhomologous chromosomes homologous

chromosomesdo not pair up pair up to form bivalentschiasmata do not form and chiasmata form and

cross overcross over never occurs occurs

Differences between mitosis and meiosis

Mitosis Meiosisone division two divisionsthe number of chromosomes the number ofremains the same chromosomes is halvedhomologous chromosomes homologous chromosomesdo not pair up pair up to form bivalentschiasmata do not form and chiasmata form and cross overcross over never occurs occursdaughter cells are geneticallyidentical

Differences between mitosis and meiosis

Mitosis Meiosisone division two divisionsthe number of chromosomes the number ofremains the same chromosomes is halvedhomologous chromosomes homologous chromosomesdo not pair up pair up to form bivalentschiasmata do not form and chiasmata form and cross

overcross over never occurs occursdaughter cells are genetically daughter cells are

geneticallyidentical different from the parent cells

Differences between mitosis and meiosis

Mitosis Meiosisone division two divisionsthe number of chromosomes the number ofremains the same chromosomes is halvedhomologous chromosomes homologous chromosomesdo not pair up pair up to form bivalentschiasmata do not form and chiasmata form and cross

overcross over never occurs occursdaughter cells are genetically daughter cells are

geneticallyidentical different from the parent cellstwo daughter cells are formed

Differences between mitosis and meiosis

Mitosis Meiosisone division two divisionsthe number of chromosomes the number ofremains the same chromosomes is halvedhomologous chromosomes homologous chromosomesdo not pair up pair up to form bivalentschiasmata do not form and chiasmata form and cross

overcross over never occurs occursdaughter cells are genetically daughter cells are geneticallyidentical different from the parent cellstwo daughter cells are formed four daughter cells are formed