Think about… Why do you not look exactly like your parents? Why do you not look exactly like your...
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Transcript of Think about… Why do you not look exactly like your parents? Why do you not look exactly like your...
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 chromosomes2. Each gene occupies a specific spot on a
chromosome3. 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 # haploid #humans 46 23goldfish 94 __dog 78 __fruit fly 14 __
• 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
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
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
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 non-sister 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)
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.
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 IMetaphase I- tetrads line up along middle
Anaphase IAnaphase 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 ITelophase 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.