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Think about… Why do you not look exactly like your parents

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Presentation on theme: "Think about… Why do you not look exactly like your parents"— Presentation transcript:

1 Think about… Why do you not look exactly like your parents
Think about… Why do you not look exactly like your parents? Why do you not look exactly like your siblings?

2 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.

3 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

4 Chromosome Number Each species has a specific # of chromosomes
diploid # haploid # humans goldfish 94 __ dog 78 __ fruit fly 14 __ Diploid cell (2N)- cell with __ copies of each chromosome Haploid cell (N) - cell with __ copy of each chromosome

5 Homologous Chromosomes
Paired chromosomes w/ genes in same locations Each chromosome can have a different form of the gene called an _______ Example:

6 Karyotype- visual display of homologous chromosomes

7 Human Life Cycle

8 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

9 Meiosis

10 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

11 What occurs during interphase?

12 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?

13 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

14 Essential Question: How does meiosis increase genetic variation among offspring?
9.6 Vocabulary: crossing over, genetic recombination

15 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)

16 Figure 9-19 Crossing Over

17 Assortment of Chromosomes Figure 9-18
Assortment of Chromosomes Figure 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. Number of possible combinations of alleles in gametes is equal to 2n where n is the haploid number. For a human, n=23 therefore about 8 million possible chromosome combinations.

18 Essential Question How does the process of mitosis compare to meiosis?

19 Mitosis vs. Meiosis

20 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

21 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

22 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.

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