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

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 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)

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 QuestionHow 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 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.