Meiosis

Meiosis

A two-division sexual reproduction method to produce gametes with half number of chromosomes

diploid

an organism or cell having the normal amount of DNA per cell

haploid

an organism or cell having only one complete set of chromosomes

Gametes

Sex cells (egg or sperm)
Have half the amount of chromosomes

Synapsis

Homologous chromosomes come together to form a tetrad

Tetrad

2 chromosomes or 4 sister chromatids (sister or non-sister chromatids)

Locus

the specific site of a particular gene on its chromosome

Interphase 1

similar to mitosis ____________
Centriole pairs duplicate
Nucleus and nucleolus still visible

Meiosis 1

A 4-part cell division that reduces the chromosome number by one-half

Prophase 1

Longest and most complex phase (90%)
Chromosomes condense
Synapsis occurs to form a tetrad

Homologs

Non-sister chromatids
Contain DNA that codes for the same genes, but different versions of those genes
Genes occur at the same location (loci)

Homologous chromosomes

pair of chromosomes (maternal and paternal) that are similar in shape and size

Tetrads

homologous pairs
carry genes controlling the same inherited traits
Each locus is in the same position on homologues

23 pairs

How many pairs of homologous chromosomes do humans have?

Autosomes

first 22 pairs of chromosome pairs

sex chromosomes

last pair of chromosomes

Crossing over

segments of non-sister chromatids break and reattach to the other chromatid
may occur between non-sister chromatids at sites called chiasmata

Chiasmata

Where chromosomes touch each other and exchange genes (crossing over)

Genetic recombination

the exchange of genetic material between different organisms which leads to production of offspring with combinations of traits that differ from those found in either parent

Meiosis 1

Homologs separate

Prophase 1

Nucleus and nucleolus disappear
Spindle forms
Chromosomes coil and Synapsis occurs
Tetrads form and crossing over occurs

Metaphase 1

shortest phase
tetrads align on the equator
Independent assortment occurs
Chromosomes separate randomly causing genetic recombination

2^n

formula to find how many different combinations of sperm a human male could produce

8 million

how many combinations can a human male produce

Anaphase 1

Homologous chromosomes separate and move towards the poles
Sister chromatids remain attached at their centromeres

Telophase 1

Each pole now has haploid set of chromosomes
Cytokinesis occurs and two haploid daughter cells are formed

Meiosis 2

Sister chromatids separate

Quick Note

No interphase 2 or very short
NO DNA replication

Mitosis

Meiosis 2 is similar to ___________

Prophase 2

Same as _________ in mitosis
Nucleus and nucleolus disappear
chromosomes condense
spindle forms

Metaphase 2

Same as __________ in mitosis
Chromosomes (not homologs) line up at equator

Anaphase 2

Same as _____________ in mitosis
Sister chromatids separate

Telophase 2

Same as ________________ in mitosis
Nuclei and nucleoli reform, spindle disappears
cytokinesis occurs
4 haploid daughter cells are produced
these cells are called Gametes

3 sources of genetic recombination

Crossing over
Independent assortment
random fertilization