Mrs. K—Biology I
Chapter Ten
Sexual Reproduction & Genetics
MEIOSIS
CHROMOSOME AND CHROMOSOME NUMBER
 Every characteristic—_________________________, is called a _______________.
 Instructions for traits are located on _______________________.
 The DNA on chromosomes is arranged in segments called ________ that control the
production of _____________.
 Humans have _____ chromosomes, ______ from each parent.
 The chromosomes that make up a pair (one from each parent) are called _________________
__________________________.
 Homologous chromosomes _____________________________________________________
___________________________________________________________________.
Homologous
chromosomes
 To maintain chromosome number from generation to generation, organisms produce
gametes—___________________________________________________________________.
 n = __________________________________________________________________.
 A cell with n chromosomes is called a __________________ cell.
 A cell with 2n chromosomes is called a __________________ cell.
MEIOSIS

Gametes are formed through a process called ________________—a type of cell division that
reduces the number of chromosomes.

Meiosis occurs in the reproductive structures (ovaries, testes) of organisms that reproduce
sexually (in human females, this takes place in utero; in human males, this begins at sexual
maturation and continues for the duration of the lifespan).

Meiosis involves two consecutive cell divisions—__________________________________.
Prophase I

Duplicated homologous chromosomes begin _________________________________________.

The homologous pairs are __________________________________ (see Fig. 10.3 on pg. 272).

During this process, certain chromosomal segments can be exchanged between two of the
homologous chromatids (this is called ____________________________).

Otherwise, prophase I is similar to prophase in mitosis.
Metaphase I

In metaphase I, the ________ of homologous chromosomes line up at the cell’s equator and the
spindle fibers attach to the centromere of each homologous chromosome.
This is different from metaphase in mitosis, in which each chromosome lines up individually,
without regard to its homologous partner.
Anaphase I

During anaphase I, __________________________________________________.

In mitosis, the sister chromatids are split in this phase, but in meiosis, each chromosome
________________________________________________________________.
Telophase I

The homologous chromosomes, each consisting of ________________________, reach the cell’s
opposite poles.

Each pole now contains only ______________________________________________________.

The sister chromatids may not be identical because _____________________________________
______________________________________________________________.

Cytokinesis usually occurs during telophase I, resulting in two cells—however, the process is not
yet complete. Meiosis II remains.
Meiosis II

Meiosis II unfolds very much like mitosis.

In metaphase II, the chromosomes line up at the equator.

In anaphase II, the sister chromatids are pulled apart at the centromere by the spindle fibers.

Cytokinesis occurs at the end of Meiosis II, and the end result is _____________________.

Meiosis is important because it results in _____________________________.