Genes

Genes A gene is the entire

sequence of DNA bases responsible for the synthesis of a protein.

A mutation occurs when the sequence of bases in a gene is altered.

Mutations may interfere with the ability to produce vital protein and may lead to a new variety within the species, hence, evolution.

Genes Recently, geneticists have

learned that only some parts of genes, called exons, are actually transcribed into mRNA (most of the nucleotide sequences in genes are not expressed during protein synthesis.

Some noncoding sequences, called introns, are initially transcribed into mRNA and then clipped out.

Regulatory Genes

• Genes that code for the production of proteins that can bind to DNA and modify the action of genes.

• Many are active only during certain stages of development.

Homeobox Genes (Hox genes)

• An evolutionarily ancient family of regulatory genes (highly conserved) that directs the development of the overall body plan and the segmentation of body tissues.

Homeobox mutationHomeobox mutation

Cell Division Cell division results in production of new cells. During cell division:

Cells are involved with normal cellular and metabolic processes.

The cell’s DNA becomes tightly coiled.DNA is visible under a microscope as chromosomes.

Chromosome Structure

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

• 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.

Chromosomes and Genetics

• Each species is characterized by a specific number of chromosomes (see chart on pg. 59). – Humans have 46 chromosomes.

Humans 46

Chicken 78

Corn 20

Housefly 12

Types of Chromosomes Autosomes - govern all physical characteristics

except sex determination. Sex chromosomes - X and Y chromosome.

Mammal females have two X chromosomes.

Mammal males have one X and one Y chromosome.

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…

Mitosis

• The cell is involved in metabolic activities.

• DNA replication occurs, but chromosomes are not visible.

Mitosis

• The nuclear membrane disappears, and double-stranded chromosomes are visible.

Mitosis

• The chromosomes align themselves at the center of the cell.

Mitosis

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

Mitosis

• The cell membrane pinches in as the cell continues to divide.

• The chromosomes begin to uncoil (below).

Mitosis

• After mitosis is complete, there are two identical daughter cells.

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

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.

Problems with Meiosis

• In order for fetal development to occur normally, the meiotic process needs to be exact

• If chromosomes or chromosome strands do not separate during either of the two divisions, serious problems can develop

• Failure to separate is called nondisjunction

Recombination

• Sometimes called crossing over; the exchange of genetic material between partner chromosomes during meiosis.

Mitosis

Meiosis

Evolutionary Significance of Meiosis

• Meiosis and sexual reproduction are highly important evolutionary innovations.

• Meiosis increases genetic variation at a faster rate than mutation.

• Offspring in sexually reproducing species represent the combination of genetic information from two parents.

Recombinant DNA Technology

• A process in which genes from the cell of one species are transferred to somatic cells or gametes of another species.

• Human genes inserted into bacterium produce genetically-needed material like Insulin.

• Genetic manipulation…

Clones Organisms that are genetically identical to another

organism. The term may also be used in referring to genetically

identical DNA segments, molecules, and cells.