Protein Synthesis Test – Tomorrow!

Meiosis

Similarities and Differences between Mitosis and Meiosis

Mitosis MeiosisWhere does it occur in body?# Cell divisions# DNA replicationsCreates what type of cell?# Chromosomes in End product# Cells producedFunction

Mitosis Review

• IPMAT

• Remember: Mitosis = Two Cells

“Tea for Two”

Reasons for Mitosis

• Production of 2 daughter cells that are genetically identical

• Provides:– a) a means of asexual reproduction for unicellular

organisms– b) replacement of worn out and damaged cells– c) growth of an organism

From Zygote to Embryo

Zygote2n

Zygote

2n

Cleavage

Blastula

From Zygote to Embryo

Meiosis

• Special type of cell division that produces haploid (n) sex cells (gametes)

• Meiosis is divided into 2 stages: Meiosis I and Meiosis II

• Consists of 1 replication and 2 divisions

Formation of gametes

46

46

23 23

How many chromosomes will baby have?

Germ Cells• Male

– Sperm producing machines– Germ cells are found in the lining of the

seminiferous tubules (250m in each testicle)– Once they reach maturity, they constantly divide

(Spermatogenesis)

• Female – Germ cells - found in follicles in ovaries and

produced before birth– Cells are suspended in Prophase I and don’t

continue to divide until puberty– Complete their division after being simulated by

hormones during the menstrual cycle (Oogenesis)

Male Female

Similarities and Differences between Mitosis and Meiosis

Mitosis MeiosisWhere does it occur in body?# Cell divisions# DNA replicationsCreates what type of cell?# Chromosomes in End product# Cells producedFunction

Let’s carry out an example for a mosquito cell Diploid Number (2n) = 6

• Period of growth of germ cells• DNA replicates

Interphase I

Early Interphase I Late Interphase I

Prophase I

• Nuclear envelope disappears• Replicated chromatin coils into chromatid pairs

• Centrioles move to opposite poles of the cell and start producing protein fibers that form the spindle

Prophase I

• Synapsis – Chromatid pairs attach to form tetrads

• Crossing over – During synapsis, arms of chromatid pairs exchange

segments of DNA at chiasma– Increases genetic diversity

Prophase I

Early Prophase I Late Prophase I

Meiosis I – Metaphase I

• Tetrads line up at the equator of spindles

Meiosis I – Anaphase I

• Tetrads separate in an event called disjunction

• Chromatid pairs are pulled to poles of cell• Cleavage furrow begins to form

Meiosis I – Telophase I

• Cleavage furrow formation is complete and cytokinesis occurs

• Nuclear envelope reappears

Meiosis II – Prophase II

• Most cells skip Interphase II and proceed right into Prophase II

• Meiosis II follows the stages of Mitosis

Meiosis II – Metaphase II

Meiosis II – Anaphase II

Meiosis II – Telophase II

Differences of Meiosis and Mitosis • Synapsis

– Happens in Prophase I– Tetrad formation

• Crossing over– Happens in Prophase I– Arms of chromatids in a

tetrad swap DNA– Increases genetic diversity

• Disjunction– Happens in Anaphase I– Tetrads separate and

chromatid pairs are pulled to opposite sides of the cell

• Non-Disjunction– Happens in Anaphase I– A tetrad does not separate

and sex cells are formed with abnormal chromosome numbers

Meiosis Square Dance

Step by Step Meiosis Animation

Dry Lab

In which phases will these terms be present?

• Chromatin• Replicated Chromatin• Chromatid Pairs• Tetrads • Chromosomes

Draw the stages of Meiosis from Metaphase I to Telophase II if non-

disjunction were to occur