Download Homologous Chromosomes

Think about…
Why do you not look exactly like
your parents? Why do you not
look exactly like your siblings?
Essential Question:
How does meiosis function in sexual
reproduction?
9.5 Vocabulary: meiosis, karyotype, homologous chromosome,
sex chromosome, diploid, gamete, haploid, fertilization, zygote,
tetrad, sister chromatids.
Access Prior Knowledge on
Chromosomes
Chromosomal Theory of Heredity
1. Genes found on chromosomes
2. Each gene occupies a specific spot on a
chromosome
3. Each chromosome carries a single allele for
each gene it has
* allele- different forms of genes are called
alleles
Chromosome Number
• Each species has a specific # of chromosomes
diploid #
humans 46
goldfish 94
dog
78
fruit fly 14
haploid #
23
__
__
__
• Diploid cell (2N)- cell with __ copies of each
chromosome
• Haploid cell (N) - cell with __ copy of each
chromosome
Homologous Chromosomes
• Paired chromosomes w/ genes in same
locations
• Each chromosome can have a different form
of the gene called an _______
• Example:
http://www.biologie.uni-hamburg.de/b-online/library/cat-removed/xover.gif
Karyotype- visual display of homologous
chromosomes
http://www.radiographicceu.com/images/article_pics/13karytype.jpg
Human Life Cycle
MEIOSIS
•
•
•
•
Occurs in…
Create ____ haploid cells from ___ diploid cell
Need to …
A human diploid cell has _____ pairs of
chromosomes; meaning ____ copies of each
• One was donated by the ______ and the other from
the ________ at fertilization(which is_____
_______________________________________)
• Steps of meiosis very similar to those of ________
• Each diploid cell undergoes Meiosis I and Meiosis
II
Meiosis
Stages of Meiosis- a cell must
undergo Meiosis I and II to form
gametes
• Meiosis I Stages:
- Prophase I
- Metaphase I
- Anaphase I
- Telophase I
• Goal: To separate
homologous
chromosomes
• Meiosis II Stages
- Prophase II
- Metaphase II
- Anaphase II
- Telophase II
• Goal: To separate
sister chromatids
What occurs during
interphase?
Meiosis I
• Chromatin condenses into
structures called
__________
• Homologous chromosomes
synapse forming _______
and crossing over occurs
during
__________________
• Homologous chromosomes
separate from each other
during ______________
• Two haploid cells are
formed at the end of
telophase I.
• Each chromosomes still
consists of sister chromatids
What is the starting cell’s
diploid number?
Meiosis II
• Each haploid cell resulting from meiosis I undergoes meiosis II to
separate ________________
• After chromosomes line up during ___________ II, the sister
chromatids will be separated during _____________ II.
• In the end, four haploid cells each having only one allele of each gene
Essential Question:
How does meiosis increase genetic
variation among offspring?
9.6 Vocabulary: crossing over, genetic recombination
1. Crossing Over
• A pair of homologous
chromosomes form a
______________ during prophase
I
• The tetrad consists of _____
chromatids
• At this time _________
_________ occurs; when nonsister chromatids of homologous
chromosomes may exchange
portions of their chromatids;
result, new combo of alleles, this
is a major source of
_____________ w/in a species
(genetic recombination)
Figure 9-19
Crossing
Over
2.
Assortment of Chromosomes
Figure 9-18. In a diploid cell with four chromosomes
(two homologous pairs) there are two equally possible
ways for the chromosomes inherited from the two
parents to be arranged during metaphase I.
Essential Question
How does the process of mitosis
compare to meiosis?
Mitosis vs.
Meiosis
An aside on Chromosomes
• Each chromosome in an homologous pair carries
the same set of genes and each gene is located at
exactly the same spot
• However, different forms of genes called alleles
exist
• An example is for earlobes; two alleles, one for
“free” earlobes and the other for “attached
earlobes”
• A person can inherit two of the same alleles, or
one of each
Sillyfilly
(extra practice with an imaginary creature)
species chromosome number is 4
• Before prophase I begins DNA
has been ________________
• Sillyfilly now has ___
chromosomes but each is
doubled, we call these
_________ _______________.
• ______________ chromosomes
(pair of chromosomes that
carry the same genes) arrange
themselves into their
respective pairs in prophase
I
Prophase I
Metaphase I- tetrads line up along
middle
Anaphase I- homologous pairs separate, one of each
moves to opposite side; each chromosome and all the
alleles on it segregate independently of any other;
this is another source of genetic recombination; also
genes are not attached in any way to each other except
for those located on the same chromosome; this
allows alleles to assort independently; genes linked
together on same chromosome are inherited together,
therefore they are called ______________ _________
Telophase I- cell membrane pinches in; each new
cell will have ____ chromosomes; however due to
________ _______ , segregation of ________, and
___________________ __________________ the
two new cells are NOT identical to each other or the
original diploid cell.