Mendelian Genetics

Your genes, located on your chromosomes contain dominant and recessive traits which were inherited from your parents and grandparents.

Some of your characteristics are caused by only one gene from each chromosome.

Traits that show themselves over recessive or hidden traits

Remember that genes come in pairs- if only one is dominant the organisms will show that trait

Examples: Tongue rolling, Detached earlobes

Traits that are masked or hidden by a dominant trait

Genes come in pairs- if only one is recessive it will not be expressed in the individual

Examples: Attached earlobes, straight thumb

Gregor Mendel Austrian Monk Experimented with

pea plants and noticed that they contained “factors” that were passed to offspring.

Dominant

Recessive- you must have two genes to have this trait

Detached Earlobes are dominant- only one gene of the pair necessary

Attached- recessive

Hitchhikers' Thumb- Dominant

Straight Thumb- Recessive

Index Longer than Ring- Dominant

Ring Longer than Index- Recessive

Peak- Dominant Straight- Recessive

Counter-Clockwise- Recessive Clockwise-Dominant

Homework Solutions

B b

B

b

____%white

2. Black fur (B) in guinea pigs is dominant over white fur (b). Find the probability of a hybrid offspring in the cross: BB x Bb

B B

B

b_______% hybrid

3. Black fur (B) in guinea pigs is dominant over white fur (b). Find the probability of a purebred offspring in a cross: BB x BB

B B

B

B_____% purebred

4. bb x bb

b b

b

b

_________% black

5. Find the probability of an offspring with the same phenotype as its parents in a cross between a purebredblack and a hybrid black guinea pig.

_____% same phenotypes as parents

6. Bb x bb

B b

b

b

__________% white

Two traits combine or blend together to produce a different trait.

There is no dominant or recessive trait. Instead, both traits have about the same influence on the organism.

Use different letter for each trait: bb= black ww= white bw=gray

BB x WW = BW

RR or BB x WW= RW or BW

RR x WW = RW