Download Meiosis - Mercer Island School District

Meiosis
Meiosis is the type of cell division for that produces the
______________ cells ( ______________ ) which are also
known as gametes.
Two important characteristics of meiosis is that it reduces
the number of chromosomes to half of the parent cell and
it creates ___________________.
Somatic Cells vs. Gametes
Somatic cells are body cells (nerve cells, muscle
cells, epithelial cells…).
These cells all have different appearances and
functions but have the same genetic information.
Gametes are the reproductive cells - the egg or the
sperm.
Gametes __________________________________
_______________________.
If Meiosis Did NOT Occur
If two parental cells combined that had the
parents full set of 46 chromosomes:
The first generation of offspring would have____
chromosomes.
The next generation of offspring would have ____
chromosomes…
Homologous Chromosomes
Most cells in a human (and in most eukaryotic organisms)
contain two copies of each chromosome.
These chromosomes are not identical (one is from the
mother and one from the father), but they ________
_______________. These pairs are called homologous
chromosomes.
Homologous chromosomes may contain different forms
of a gene for the same trait.
Brown eyes
Green eyes
Humans have 23 pairs of chromosomes, for a
total of 46 chromosomes in each somatic (body)
cell.
Autosomal chromosomes: Chromosomes _________,
which form homologous pairs in both males and
females.
Sex chromosomes: Chromosome 23. Determines
gender (XX= female, XY= male). For males, this pair is
____________________________________________
Diploid and Haploid Cells
Diploid cells have homologous
pairs of chromosomes. (2 of each
chromosome)
Human somatic (body) cells are
diploid. (di = 2)
Haploid cells ______________
_______________________.
Gametes (egg and sperm) cells
are haploid.
When fertilization occurs (fusion of egg and
sperm) the diploid number is restored.
Diploid cells are represented by 2n and
haploid by n, where n is the number of
different chromosomes.
Examples:
Organism
Human
Gamete (n)
23
Body cell (2n)
46
Pea Plant
7
___
Fruit Fly
__
8
Dog
39
___
Indian Fern
____
1260
Discuss with your table partner:
• Review the term sister chromatids. When do cells
have sister chromatids?
_________________________________________
• What are homologous chromosomes? What kind of
cells have homologous chromosomes?
__________________________________________
• What do the terms diploid and haploid mean?
What kind of cells are diploid? What kind of cells
are haploid?
Interpreting Genetics Diagrams
• Homologous chromosomes are indicated by length.
• Sister chromatids (identical copies produced during S
phase of interphase) are shown connected by centromere.
• Genes are represented with letters. Example: R/r
represents gene for pea seed shape
• Different forms of the same gene are represented with
capital versus lower case letters.
Example: R represents round shape form of the gene, r
represents wrinkled shape form of the gene.
Overview of Meiosis
In meiosis, __________________ of
chromosomes is followed by ___cell divisions,
to produce __ __________cells.
Phases of Meiosis
As with mitosis, meiosis is preceded by
an interphase period,
during which the chromosomes are
duplicated.
The two sister chromatids are
___________________.
The homologous pairs have the
same genes, but could have
different alleles (forms of the
gene).
At the start of meiosis, there are
____ copies of each gene.
Review with your table partner:
The basic phases of meiosis are similar to those of
mitosis (with some key differences).
Review with your table partner what happens in
each of the following phases of mitosis:
Prophase, Metaphase, Anaphase,
Telophase/Cytokinesis
Prophase I
During Prophase I,
the chromosomes
_____________ to become
visible.
______________________
_______________________
_______________________
(Homologous pairs never form tetrads during
mitosis).
Metaphase I
In metaphase I,
the _______________
__________ ___________
along the middle of the
spindle.
Anaphase I:
HOMOLOGOUS PAIRS
separate.
Telophase I
Nuclei reform, producing
2 haploid daughter cells.
But each cell still has ___
______________________
______________________
Meiosis II separates the sister chromatids.
Prophase II
Anaphase II
Metaphase II
Telophase/
cytokinesis II