Ch. 12: mitosis, Meiosis, and life cycles

How does a plant grow?

• Cell cycle– Activities of a cell from one cell division to

the next

What is a chromosome?

• =

• Cabbage: 18

• Cotton: 52

• Mango: 40

• Corn: 20

• Foxglove: 56

• Oak tree:24

Fig 8.7

The Events of the Interphase

• Interphase:

– Divided into 3 phases:

G1 –

S –

G2 – cell growth after DNA replication; cell prepares to divide

Cell Division or “M” phase

• Cell Division consists of two parts

1. Mitosis:

2. Cytokinesis:

• What needs to happen to the chromosomes prior to Mitosis?

• During mitosis?

Fig 8.6

Each chromatid has one DNA molecule

Centromere

Sister chromatids

1. How do sister chromatids compare genetically?

2. What happens to sister chromatids during mitosis?

Sketch of one duplicated chromosome

Mitosis: sister chromatids separate

Two-chromatidchromosome

Interphase

S-Phase: DNA Replication

One-chromatidchromosome

One-chromatidchromosome

The number of chromosomes in each daughter cell is the same as the number of chromosomes in the parent cell

Mitosis: Division of the Nucleus• Four Stages:

1. Prophase – 1. .2. .3. Chromosomes attach to spindle fibers

2. Metaphase – Spindle fibers align the chromosomes at the equator of the cell

3. Anaphase –

4. Telophase – nuclear envelope forms around each cluster of chromosomes

Fig 8.8

Cytokinesis: division of the cytoplasm to create 2 new cells

Fig 8.9

• Mitosis

• Meiosis– A reductive division (46 C 23 C) – Daughter cells are genetically different

Normal Karyotype of Human

Chromosomes

• Karyotype =

• How many pairs of chromosomes in this Karyotype?

• Paired chromosomes are homologous =

Diploid cell: 3 sets of homologous

chromosomes

One set ofnon-homologouschromosomes

Haploid cell

One set of non-homologous

chromosomes

Haploid cell

• Diploid cell –

• Haploid cell – contains only ONE chromosome of each pair (n)

Meiosis

• Only occurs within the male and female sporangium (all other cell divisions are mitosis)

Fig 8.15

Fig 8.16 Meiosis I

Stages of Meoisis1. Interphase – same as mitosis (G1, S, G2)2. Meiosis I

a) Prophase I –

b) Metaphase I – c) Anaphase I – d) Telophase I –

3. Meiosis IIa) Prophase II – chromosomes attach to spindleb) Metaphase II – chromosomes align at equatorc) Anaphase II – sister chromatids separated) Telophase II – cells divide, end result = 4 haploid

daughter cells

Plant sexual life cycles: Alternation of Generations

• 2 multicellular life stages:1. Sporophyte:

• Spores – haploid cells that can grow into a new, multicellular, haploid organism (the gametophyte) without fusing to another cell.

2. Gametophyte:

• Egg & sperm fuse to form the diploid zygote, which divides by mitosis to form the sporophyte