Chapter 4

Heredity and Evolution

DNA DNA is found in the

nucleus of cells, organized into single-stranded chromosomes, and tells the cell how to function and what type of cell it’s supposed to be (i.e. liver cell, hair cell, skin cell, bone cell, etc.)

DNA is made of nucleotides (a sugar, a phosphate and one of four nitrogenous bases)

Review…

How DNA gets copied

RibosomesRibosomes

NucleusNucleus

DNADNA

Review…

Every cell must contain the genetic information and the DNA is therefore duplicated before a cell divides (replication)

After the DNA replicates inside the cell’s nucleus, it must get it’s message outside the nucleus…

…through the goopy cytoplasm of the cell…

…and into the Ribosomes! RNA

CytoplasmCytoplasm

A chromosome is composed of a DNA molecule and associated proteins.

A gene is the entire sequence of DNA bases responsible for the synthesis of a protein.

Genes and ChromosomesReview…

Exons are the only parts of genes that are expressed in an individual.

People also have Introns in their genes, copied faithfully copied by the mRNA that are later clipped out and not expressed for some reason not yet known.

GenesReview…

Chromosome Structure During normal cell

functions, chromosomes exist as single-stranded structures.

During cell division, chromosomes consist of two strands of DNA joined at the centromere.

Since the DNA molecules have replicated, one strand of a chromosome is an exact copy of the other.

Review…

Mitosis Mitosis is cell division in somatic cells. Mitosis occurs during growth and

repair/replacement of tissues. The result of mitosis is two identical

daughter cells that are genetically identical to the original cell.

Here’s the steps…

Review…

Mitosis The cell is involved in

metabolic activities. DNA replication

occurs, but chromosomes are not visible.

Review…

Mitosis The nuclear

membrane disappears, and double-stranded chromosomes are visible.

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Mitosis The chromosomes

align themselves at the center of the cell.

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Mitosis The

chromosomes split at the centromere, and the strands separate and move to opposite ends of the dividing cell.

Review…

Mitosis The cell membrane

pinches in as the cell continues to divide.

The chromosomes begin to uncoil (below).

Review…

Mitosis After mitosis is

complete, there are two identical daughter cells.

The nuclear membrane is present, and chromosomes are no longer visible.

Review…

Meiosis Cell division in

specialized cells in ovaries and testes.

Meiosis involves two divisions and results in four daughter cells, each containing only half the original number of chromosomes.

These cells can develop into gametes.

Review…