1. Model and explain how genetic information is transferred from one generation of cells to the next via the processes of mitosis and meiosis

2. Compare and contrast cell division by mitosis with cell division by meiosis

3. Represent chromosomes containing specific alleles through cell division by mitosis and meiosis

ObjectivesObjectives

Meiosis: sexMeiosis: sex

Last time:Last time:

Complete in your groups.Turn in one paper per group at the end of class.

Draw a cell containing 2 pairs of unreplicated homologous chromosomes for the individual to the right.

She is heterozygous for tongue rolling and earlobe shape.

Modeling the steps of meiosisModeling the steps of meiosis

DNA replicatesDNA replicates

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G2: Cell DNA is replicated

G2: Cell DNA is replicated e

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Two Divisions:

1. Meiosis 1: Homologs separate (crossing over and independent assortment)

2. Meiosis 2: Sister chromatids separate

Cell Division by Meiosis Cell Division by Meiosis

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tHomologs align at equatorial plane

Prophase 1Prophase 1

Draw your cell with homologous pairs aligned at the equatorial plane

Draw your cell with homologous pairs aligned at the equatorial plane

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Metaphase 1Metaphase 1

How is this different from metaphase of mitosis?

Crossing-overCrossing-over

Homologous pairs align, then separate

Metaphase – Anaphase 1: Metaphase – Anaphase 1:

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First Division (Meiosis 1)First Division (Meiosis 1)Homologs sort into different daughter cells. Draw the products of this division.

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2 cells – each with 1 member of homologous pair.End of Meiosis 1End of Meiosis 1

Are there other possibilities? What is the consequence of separating the homologous pairs?

1. Law of Independent Assortment– Each pair of homologous chromosomes

positions independently of all other pairs in Metaphase 1

Mendel’s LawsMendel’s Laws

Centromeres of sister chromatids align at equatorial plane.

Metaphase 2: Metaphase 2:

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Metaphase 2:

Second Division (Meiosis 2)Second Division (Meiosis 2)Each cell resulting from Meiosis 1 divides. Sister chromatids separate at the centromere and sort into different daughter cells. Draw the products of this division.

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Sister chromatids separate into daughter cells

Metaphase – Anaphase 2:

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Sister chromatids separate into daughter cells

Metaphase – Anaphase 2:

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End of Meiosis 2: Daughter cells are “gametes” (eggs and sperm).

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Genotypes of gametes?

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What if homologs lined up differently at Meiosis 1?

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Predict the genotypes of gametes.

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Genotypes of gametes?

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Why are the genotypes different?

1. Law of Independent Assortment- Each pair of homologous chromosomes

positions independently of all other pairs in Metaphase 1;

2. Law of Segregation- Two alleles of a given gene segregate during gamete formation, in Metaphase 2.

Mendel’s LawsMendel’s Laws

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What is the consequence of Independent Assortment?

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What would happen if . . .?

Why doesn’t this work??

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Can we predict the number of different types of gametes that could be formed?

i.e., How many different allele combinations (genotypes) could you get in the gametes?