Inherited traits

Mendel’s Legacy

The “Father” of genetics.

Studied inherited traits in pea plants

Discovered dominant and recessive traits and was able to predict what pea offspring would look like!

A Mendelian Genetic Primer

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Genes come in pairs that separate in the formation of gametes, or sex cells.

The members of the pair may be identical (homozygous) or non-identical (heterozygous).

Each form of a particular gene is called an allele

For simplification, only two alleles of a given gene are possible in an individual although many alleles of a gene are possible within a population.

One allele is dominant over another (or so Mendel believed).

A Mendelian Genetic Primer

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A Mendelian Genetic Primer

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Genotype: What alleles the organism has.

Phenotype: How the alleles are expressed. Often, this means what the organism looks like.

Why is this not always the case?

Hold up one or more of the three response cards to answer the following prompts…

Homozygous

Heterozygous

Homozygous Recessive

One dominant allele and one recessive allele

Homozygous Dominant

Heterozygous

Homozygous Recessive

Homozygous Dominant

Heterozygous

A species of rabbit can have either brown fur, or white fur (there is no in-between). The brown fur allele is dominant, and the white fur allele is recessive.

What genotype(s) can a rabbit with brown fur have?

A species of rabbit can have either brown fur, or white fur (there is no in-between). The brown fur allele is dominant, and the white fur allele is recessive.

What genotype(s) can a rabbit with white fur have?

Different Genotypes Can Produce the Same Phenotype

Two rabbits are brown and each have one copy of the gene for brown fur and one of the gene for white fur.

What are their genotypes?

Two rabbits are brown and each have one copy of the gene for brown fur and one of the gene for white fur.

What are the chances that one of their offspring will have white fur?

We combine the father’s genotype with the mother’s genotype.

It doesn’t matter which parent goes on which part of the square.

The four squares represent the 4 possible offspring these parent can have with regard to this one gene.

Now lets fill in the squares to see what offspring are possible.

What is the genotype of offspring #1?

What is the genotype of offspring #2?

What is the genotype of offspring #3?

What is the genotype of offspring #4?

Now we see the 4 possible offspring for this mating.

These offspring have 3 different genotypes.

BUT there are only 2 phenotypes!

What are they?

3 offspring out of the 4 have brown fur. Hold up the cards that represent the genotype(s) that make brown rabbits.

BB and Bb ¾ rabbits = 75% of

offspring If the parents have

40 offspring, how many would probably be brown?

1 offspring out of the 4 has whit fur. Hold up the cards that represent the genotype(s) that make white rabbits.

bb 1/4 rabbits = 25%

of offspring If the parents have

40 offspring, how many would probably be white?

So two brown rabbits produced some offspring that are white!

What is the genotype for white rabbits?

Some rabbits may be brown, but carry a copy of the white gene. The white gene doesn’t show up because it is recessive. What is the genotype of these rabbits?

We call organisms like these carriers of an allele, because they do not show the phenotype, but they carry the allele in their genotype.

These rabbits were not white their offspring may be.

A brown rabbit has two copies of the gene for brown fur.

What is its genotype? There is also a white rabbit.What is its genotype? The two rabbits mate, what is the

genotype of 100% of their offspring?Draw a punnett squareHold up your answerWhat color are the offspring

rabbits?

A brown rabbit has one copy of the gene for brown fur and one of the gene for white fur.

What is its genotype? There is also a white rabbit.What is its genotype? The two rabbits mate, what are the two

possible genotypes of their offspring?Draw a punnett squareHold up your answerWhat color are the offspring rabbits?

What percent of the offspring are heterozygous?

50% Hold up the card that represents these

rabbits. What color would these rabbits be?

What percent of the offspring are homozygous for the recessive allele?

50% Hold up the card that represents these

rabbits. What color would these rabbits be?

What Works for Peas Also Works for Humans

An albino woman

In the cross Bb x Bb, where B is a dominant allele for standard pigmentation and b is a recessive allele for no pigmentation (albinism).

Are the parents albino? No, because the standard

pigementation allele (B) is dominant. So it is the one the shows up!

What Works for Peas Also Works for Humans

An albino woman

In the cross Bb x Bb, where B is a dominant allele for standard pigmentation and b is a recessive allele for no pigmentation (albinism).

Are the parents heterozygous or homozygous?

Heterozygous (Bb) Why do we call the parents

carriers of the albinism gene?

What Works for Peas Also Works for Humans

An albino woman

In the cross Bb x Bb, where B is a dominant allele for standard pigmentation and b is a recessive allele for no pigmentation (albinism).

What genotype does a person need to have to look albino?

Homozygous recessive (bb)

What Works for Peas Also Works for Humans

An albino woman

In the cross Bb x Bb, where B is a dominant allele for standard pigmentation and b is a recessive allele for no pigmentation (albinism)

Draw a punnett square for this cross, to see what their children would look like.

Now we see the 4 possible offspring for this mating.

These offspring have 3 different genotypes.

BUT there are only 2 phenotypes!

What are they?

What Works for Peas Also Works for Humans

An albino woman

In the cross Bb x Bb, where B is a dominant allele for standard pigmentation and b is a recessive allele for no pigmentation (albinism)

What fraction of the offspring will be albino?

¼ will be albino. Hold up the card that

represents a person with albinism.

What Works for Peas Also Works for Humans

An albino woman

In the cross Bb x Bb, where B is a dominant allele for standard pigmentation and b is a recessive allele for no pigmentation (albinism)

What fraction of the offspring will look normal?

¾ of offspring will be normal.

Hold up the card(s) that represent(s) a person that has standard skin pigmentation.

What Works for Peas Also Works for Humans

An albino woman

In the cross Bb x Bb, where B is a dominant allele for standard pigmentation and b is a recessive allele for no pigmentation (albinism)

What fraction of the offspring will be carriers?

Hold up the card that represents a carrier.

What Works for Peas Also Works for Humans

An albino woman

In the cross Bb x Bb, where B is a dominant allele for standard pigmentation and b is a recessive allele for no pigmentation (albinism)

Hold up the card that represents a homozygous dominant genotype.

What fraction of the offspring will homozygous dominant?