Meiosis and its role in sexual reproductionThemes:OrganizationUnity and Diversity

Meiosis

Learning Objectives:

• See how meiosis and sexual reproduction can

increase genetic variation (shuffle mutations).

• Describe how the process of meiosis produces

haploid cells.

• Compare meiosis to mitosis.

• Follow-up Activity: Karyotype—Determine how

chromosomes are organized and what we can

determine from looking at homologous pairs.

Meiosis

• Cell Division that results in daughter

cells receiving half the number of

chromosomes (reduction division)o Somatic cell (body cell) – Diploid (2N)

o Gametes (sperm/ovum)- Haploid (n)

3 ways meiosis allows for genetic change

• Meiosis shuffles mutation through:o Independent assortment of chromosomes

o Crossing over

o Random fertilization

Independent assortment

Crossing over

Random Fertilization

Animations on MeiosisWe’ll use this video to stop and identify the organization of the process.

How many time does interphase occur?

What happens during meiosis I?

What happens during meiosis II?

Describe the result of meiosis?

Meiosis • Two phases : Meiosis I and Meiosis II

Meiosis I

• Goal of this phase is to create variation by crossing over between

homologous chromosomes.

• Sister chromatids are not separated during anaphase, but whole

homologous chromosomes are separated.

Meiosis

No DNA replication between Meiosis I and Meiosis II

• Meiosis II

• Sister chromatids of each homologous chromosome gets separated.

• 4 daughter nuclei is formed.

Haploid vs. Diploid

• Different organisms have a different number of

chromosomes that make up one set - (n)

Organism Body Cell Gamete

Human 23

Sweet Pea 7

Fruitfly 4

How come we have 46 chromosomes in our body cells if the gametes (sperm and egg cells have only 23)

Homologous Chromosomes• Chromosomes identical in size

and staining patterns and have the same genes

• One is inherited from father and one from the mother.

In the human body, this process forms sperm and egg (more detail next class!)

Sexual reproduction causes the cells to become Diploid again

Exit Slip

• Funny square dancing video:http

://www.youtube.com/watch?v=JKXAdwCibsA&feature=end

screen&NR=

1

• Watch the video and answer the exit slip questions.