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


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


an organism or cell having only one complete set of chromosomes


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


Homologous chromosomes come together to form a tetrad


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


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


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


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?


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


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


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


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