Meiosis and Mitosis

Prokaryote

Unicellular, no membrane bound organelles

Prokaryotic DNA does not exist in the highly order and packed arrangement

Made up of eubacteria and archaea

Eukaryote

Both unicellular and multicellular with membrane-bound organelles

Genetic material surrounded in a nuclear enveloped to form a nucleus

DNA is closely associated with histones to form tightly packed chromosomes

Viruses

Neither prokaryotic nor eukaryotic

Outer protein coat surrounding nucleic acid

Prokaryotic Cell Reproduction

Simple division: separation of replicated circular chromosome

Origin of replication

High rate of replication

Eukaryotic Cell Replication

Eukaryotic chromosomes:

• Homologous pair

• Chromosome structure

• The cell cycle

• Genetic consequences of the cell cycle

Homologous Pair

Diploid cells carry two sets of genetic information

Haploid cells carry one set of genetic information

Centromere

Attachment point for spindle microtubules

Telomeres

Tips of a linear chromosome

Origins of replication

Where the DNA synthesis begins

The Cell Cycle

Life cycle of the cell

Interphase: an extended period between cell divisions, DNA synthesis, and chromosome replication phase

M phase: mitotic phase

Phase check points: key transition points

Interphase

G1, S, G2

• G1: Growth; proteins necessary for cell division synthesized

• G1/S checkpoint: regulated decision point

• S: DNA synthesis

• G2: biochemical preparation for cell division

• G2/M checkpoint: only passed if DNA completely replicated and undamaged

M phase

Mitosis: separation of sister chromatids

Cytokinesis: separation of cytoplasm

Mitosis

• Prophase

• Prometaphase

• Metaphase

• Anaphase

• Telophase

Prophase (Mitosis)

Chromosomes condense

Each chromosome possesses two chromatids.

The mitotic spindle forms.

Prometaphase (Mitosis)

The nuclear membrane disintegrates.

Spindle microtubules attach to chromatids

Metaphase

Chromosomes line up on the metaphase plate

Telophase (Mitosis)

Chromosomes arrive at spindle poles

The nuclear membrane re-forms and the chromosomes relax

Anaphase (Mitosis)

Sister chromatids separate and move toward opposite poles

Prophase Mitosis

Prometaphase Mitosis

Metaphase Mitosis

Anaphase Mitosis

Telophase Mitosis

Genetic Consequences of the Cell Cycle

Producing two cells that are genetically identical to each other and with the cell that gave rise to them

Newly formed cells contain a full complement of chromosomes

Each newly formed cell contains approximately half the cytoplasm and organelle content of the original parental cell

Meiosis

The production of haploid gametes

Fertilization

The fusion of haploid gamates

Genetic variation

Consequences of meiosis

Meiosis

Interphase: DNA synthesis and chromosome replication phase

Meiosis I: separation of homologous chromosome pairs, and reduction of the chromosome number by half

Meiosis II: separation of sister chromatids, also known as equatorial division

Meiosis I

• Prophase I

• Metaphase I

• Anaphase I

• Telophase I

• Interkinesis

• Prophase II

• Metaphase II

• Anaphase II

• Telophase II

Prophase I (Meiosis I)

• Synapsis: close pairing of homologous chromosome

• Tetrad: closely associated four-sister chromatids of two homologous chromosomes

• Crossing over: crossing over of chromosome segments from the sister chromatid of one chromosome to the sister chromatid of the other synapsed chromosome - exchange of genetic information, the first mechanism of generation genetic variation in newly formed gametes

Metaphase I (Meiosis I)

Random alignment of homologous pairs of chromosome along the metaphase plate

Anaphase I (Meiosis I)

Separation of homologous chromosome pairs, and the random distribution of chromosomes into two newly divided cells - second mechanism of generating genetics variation in the newly formed gametes

• Homologous chromosomes separate and move toward opposite poles

Telophase I (Meiosis I)

Chromosomes arrive at the spindle poles and the cytoplasm divides

Prophase II (Meiosis II)

The chromosomes recondense

Metaphase II (Meiosis II)

Individual chromosomes line up on the equatorial plate

Anaphase II (Meiosis II)

Sister chromatids separate and move toward opposite poles

Telophase II (Meiosis II)

Chromosomes arrive at the spindle poles and the cytoplasm divides

Middle Prophase I

Chromosomes begin to condense, and the spindle forms

Late Prophase I

Metaphase I

Anaphase I

Telophase I

Prophase II

Metaphase II

Anaphase II

Telophase II

Products of Meiosis

Consequences of Meiosis and Genetic Variation

Four cells are produced from each original cell

Chromosome number in each new cell is reduced by half. The new cells are haploid

Newly formed cells from meiosis are genetically different from one another and from the parental cell

Cohesin

A protein that holds the chromatids together and is key to the behavior of chromosome in mitosis and meiosis

Spermatogensis:

Male gamete production

Oogenesis:

Female gamete production