1. What is a mutant?

2. How is hereditary information passed onfrom one generation to the next? What

are the rules?

3. The same rules apply to all plants and animals.

Concepts

Normal Fly

White Eyes Mutant

Dark Body Mutant

Tiny Wing Mutant

Wings Held-Out Mutant

A mutant is different than “normal”.

The mutant characteristic is passedon to the next generation.

normal

wing mutant

Fruit Flies

normal

wing mutant

Plants and animals have two copies of every gene.

Mom and dad each pass on only one copy of every gene to their children.

Genes are the basic units of inheritance.

One “good” copy of a gene is all that is needed to be normal.

A mutant has two “bad” copies of a gene.

Genes can be working (“good”)or broken (“bad”).

Each offspring gets one copy of the genefrom each parent.

All offspring are normal.

normal(has 2 good copies

of wing gene)

normal(has 2 good copies

of wing gene)

+/+ +/+xparents:

+/+offspring:

x

Each offspring gets one copy of the gene fromeach parent.

All offspring have 2 bad copies of wing gene.

All offspring are wingless.

-/- -/-xparents:

-/-offspring:

wingless mutant(has 2 bad copies

of wing gene)

wingless mutant(has 2 bad copies

of wing gene)

x

normal(has 2 good copies of wing gene)

mutant(has 2 bad copies of wing gene)

+/-offspring:

All offspring look normal because they onlyneed one good copy of the wing gene.

All offspring are “carriers” for a mutant copy of the wing gene.

+/+ -/-xparents:

x

carrier carrier+ / - + / -x

offspring: +/- -/+ -/-

These flies look normal because they only need one good copy of the wing gene.

These flies have no wingsbecause they have two badcopies of the wing gene.

+/+

x

Cells Communicate with Each OtherThrough Signals and Receptors

Cells Communicate with Each OtherThrough Signals and Receptors

Some signals are secreted and can travelseveral cells away.

Cells Communicate with Each OtherThrough Signals and Receptors

Some signals are tethered and can onlyinfluence adjacent cells.

Cells Communicate with Each OtherThrough Signals and Receptors

Receptors sense signals and become activated.Activated receptors act to alter gene expression.

A Morphogen is a Developmentally Important Type of Secreted Signal

Morphogens have the following characteristics:

1. They are synthesized in some but not all cells.

2. They diffuse from the site of synthesis and are lessconcentrated the farther away from the source of synthesis.

3. Cells respond to different morphogen concentrations byactivating expression of distinct sets of genes.

Morphogens

The dpp gene promotes skin development.

In dpp mutants, skin is replaced bynervous system.

The dpp gene is normally expressed incells that will form skin.

What would happen if the dpp gene wasmisexpressed in cells that would normallyform the nervous system?

Misexpression Experiment

Ventral

Normal embryoDorsal

Misexpression of dpp converts cells thatwould normally form nervous system intoskin.

The ag gene promotes stamendevelopment

normal ag mutant

petal stamen

The ag gene is normallyexpressed in stamens

normal ag mutant

What would happen if the ag gene wasmisexpressed in cells that would normallyform petals?

Misexpression Experiment

ag mutantnormal ag misexpression

Misexpression of ag causes cells that wouldnormally form petals to form stamens.