Ch.3 The Chromosome Theory of Inheritance

Mitosis

Nuclear division that generates two daughter cells containing the same number and type of chromosomes as parent cell

Meiosis

Nuclear division that generates gametes (egg and sperm) containing half the number of chromosomes found in other cells

• Haploid (n) gametes = single set of chromosomes

• 2 round of cell division

Zygote

diploid (2n) – carry two matching sets of chromosomes

Sister chromatids

identical copies of a replicated chromosome

Homologs

contain the same set of genes, but can have different alleles for some genes (one from mom and one from dad)

• same size, shape, banding

• non-homologs = complete unrelated sets of genes

Autosomes vs Sex chromosomes

A: all chromosomes except X and Y

S: unpaired X and Y

Karyotype

Micrograph of stained chromosomes arranged in homologous pairs

• EX: human male (2n = 46, n = 23)

Goals of mitosis (3)

Ultimate: produce 2 “daughter” cells that are genetically identical to parent

1. adding new cells during development

2. replacing old cells with new ones during our lifespan

Interphase

Period of cell growth and chromosome duplication between divisions

1. G1: chromosome NOT dup or replicating

2. S Phase: duplication of chromosome into sister chromatids

3. G2: synthesis of proteins for mitosis

Centrosome

microtubule organizing center near the nuclear envelope

Cells that stay in G0 (3)

1. Lens cells

2. Mature heart cells

3. Nerve cells

Prophase

Chromosomes condense and become visible

Prometaphase

• Nuclear envelope breaks down

• Microtubules from centrosomes invade the nucleus and connect to the centromere of each chromatid

• Sister chromatids attach to microtubules from opposite poles

Metaphase

• Chromosomes align on the metaphase plate with sister chromatids facing opposite poles

• Forces pushing and pulling chromosomes to or from each pole are in balanced equilibrium

Anaphase

• Centromeres of all chromosomes divide simultaneously

• Microtubules pull separated sister chromatids to opposite poles (characteristic V shape)

Telophase

• Nuclear envelope forms around each group of chromatids

• Chromosomes decondense

Cytokinesis

• Begins during anaphase but not completed until after telophase

• Parent cells split into two daughter cells with identical nuclei

Somatic Cells

make up vast majority of cells in the organism

• In G0 or are actively going through mitosis

Germ Cells

precursors to gametes

• Set aside during embryogenesis

• Become incorporated into reproductive organs

• Only cells that undergo meiosis to produce haploid gametes