Chapter 6Chromosomes andCell Reproduction

Important Vocabulary

Chromosomes – tightly coiled packages of DNA. Held together by proteins called histones.

DNA wraps around the histones then supercoils to form chromosomes.

Important Vocab

Chromatid – two exact copies of a chromosome held together by a centromere. Forms as DNA copies itself before cell division

Centromere – holds the chromatids together until they separate

Types of Chromosomes

Sex Chromosomes – are the chromosomes that determine the sex of an organism. Female: XX Male: XY

Autosomes – all other chromosomes Humans: 44 autosomal chromosomes

Chromosomes

Karyotype – is a picture of the chromosomes in a somatic (body) cell.

22 homologous pairs of autosomes.

2 sex chromosomes

Chromosomes

Homologous chromosomes – two copies of each autosome (maternal and paternal)

Homologous chromosomes are the same size, shape, and carry genes for the same trait. One comes from mom and one comes from dad.

Chromosomes

Diploid – cells have two sets (maternal and paternal) of chromosomes. Humans have 46 chromosomes. Represented by 2n (means a full set of DNA) Somatic Cells (cells making up the body)

Haploid – cells have one set of chromosomes. Human haploid cells have 23 chromosomes. Represented by n (means a half set of DNA) Gametes (reproductive cells : egg and sperm)

Diploid Cells Somatic Cells Cells that make

up the body of organisms.

Somatic Cells are produced through Mitosis (cell division results in 2 genetically identical cells).

Phases of the Cell Cycle

• Interphase:• G1, S, G2

• Mitosis• PMAT

• Cytokinesis

Interphase

The longest stage of a Cell’s life

The time spent between divisions

Produces all materials required

for growth

Preparation for division

Part of one of Interphase is also known as the G1 Phase of the Cell Cycle.

This is the Growth Phase where the cell grows and perfoms all of its necessary functions.

The Second part of Interphase is known as the S Phase

Synthesis Phase is when DNA replicates copying itself ensuring there will be one full copy of DNA in each daughter cell.

The third part of the Cell Cycle, G2, is a second growth phase where the cell makes the cell is ready for Mitosis.

Also a checkpoint to ensure the DNA correctly replicated.

Mitosis:Cell Division

• Mitosis has 4 phases.

• Prophase

• Metaphase

• Anaphase

• Telophase

In Prophase the nuclear envelope disintegrates, centrioles move to the poles, spindle fibers develop and begin to move chromosomes toward the center of cell.

Spindle FibersPair of Centrioles

Chromosomes consisting of 2 Sister Chromatids

During Metaphase the Chromosomes line up across center of the cell, also called the equator, or Metaphase plate.

Spindle Fibers

Chromosomes

Equator, or Metaphase Plate

In Anaphase the Chromatids that make up each Chromosome move apart and travel to opposite poles of the cell.

Daughter Chromosomes

Chromosome

In Telophase an envelope surrounds each set of Chromatids to form new Nucleus and the Cytoplasm starts to divide

Cleavage Furrow

2 identical sets of chromosomes

Cytokinesis takes place when the Cytoplasm divides and two cells with identical genetic material are formed

Daughter Cells

Let’s Review

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