1 Review Write a summary of each phase of meiosis Use Analogies Compare the chromosomes of a diploid cell to a collection of shoes in a closet. How are.

1 Review Write a summary of each phase of meiosis Use Analogies Compare the chromosomes of a diploid

cell to a collection of shoes in a closet. How are they similar. What would make the shoe collection comparable to the chromosomes of a haploid cell

2 Review What are the principle differences between mitosis and meiosis

3 Review How does the principle of independent assortment apply to chromosomes

Infer If two genes are on the same chromosome but usually assort independently, what does that tell you about how close together they are

CH 11 INTRODUCTION TO GENETICS11.4 Meiosis

Diploid Cells

Two sets of homologous chromosomes One chromosome 2 from mom and one chromosome 2

from dad Somatic cells All cells other than sex cells “2n”.

Haploid Cells

Only one set of chromosomes Gametes “n”.

Meiosis

Similar in process to Mitosis Forms gametes Goes from 2n to n

Fertilization goes from n to 2n Meiosis I Meiosis II Create FOUR haploid cells from ONE diploid cell.

Meiosis Phases

Interphase Prophase 1 Metaphase 1 Anaphase 1 Telophase 1 Cytokinesis

Prophase 2 Metaphase 2 Anaphase 2 Telophase 2 Cytokinesis.

Chromosomes Each chromosome consists of

two copies ensuring that each new cell will have the same genetic information

The identical strands of DNA are each called chromatids and are held together by a centromere.

Interphase 1 Chromosome replicate.

Prophase 1

DNA coils up into Chromosomes Nuclear membrane breaks down Chromosomes pair up into Tetrads Tetrad

Homologous pair.

Prophase 1

Crossing over may occur Chromatids of the homologous chromosomes cross

over one another Crossed sections of the chromatids are exchanged.

Metaphase 1

Homologous Pairs Line up down center of cell.

Anaphase 1

Chromosome Pairs separate Pulled to opposite poles of cell.

Telophase 1 and Cytokinesis

Nuclear membrane forms around each cluster of chromosomes

Cytokinesis occurs forming two cells.

Now have two daughter cells that are genetically different

Now are Haploid.

Prophase 2

Chromosomes become visible Nuclear membrane breaks down No additional crossing over.

Metaphse 2

Chromosomes line up in the center of each cell.

Anaphase 2

The paired chromatids separate.

Telophase 2 and Cytokinesis

Chromosomes arrive at poles Nuclear envelope reforms Cytokinesis occurs forming four cells.

Sperm Male Gamete

Ova or Ovum (egg) Female Gamete

Fertilization When the two gametes combine

Zygote Fertilized egg.

Mitosis vs. Meiosis

Creates 2 daughter cells Cell is identical to

parent Diploid (2n) 1 division Produces ‘body cells’

(somatic cells)

Creates 4 daughter cells

Genetically different from parent cell

Haploid (n) 2 divisions Produces gametes

Crossing over Genetic Variations.

You are “One in a Million” Over 8 million possible

gamete combinations from dad

Over 8 million possible gamete combinations from mom.

You are actually“One in 64 TRILLION”

Gene Linkage

The closer two genes are located on a chromosome the more likely those alleles will occur together Less of a chance for crossing over to occur in between

Used to map out location of genes.

Gene Map

Haploid and diploid numbers are designated N and 2N. The table shows haploid or diploid numbers of a variety of organisms.

Copy the table and complete it and then use it to answer the questions on the next slide.

1. Calculate What are the haploid numbers for the fern and onion plants

2. Interpret Data In the table, which organisms diploid number is closest to a human

3. Apply Concepts Why is a diploid number always even

4. Evaluate Which organism’s haploid and diploid numbers do you find most surprising- why