Genetics

Traits

• Physical characteristics

Heredity

• The passing of traits from parents to their children

Genetics

• The Scientific Study of Heredity

DNA

• The genetic material that carries information about an organism and is passed from parent to offspring.

Chromosome

• A collection of genes. The human DNA has 46 chromosomes.

Genes

• A segments of your DNA on a chromosome that code for specific traits.

Allele

• Different versions of the same gene.

BIG PICTURE

Genetics

• Geneticists look at our DNA and our physical traits to determine the outcome of future offspring

How are traits determined?• Try to bend your thumb backwards at the

joint. Some people can form at least a 45 degree angle, which is called a “hitchhiker’s thumb”. Other people have straight thumbs which do not bend this way. Which one do you have?

Straight Thumbs have the H allele, Hitchhiker’s Thumbs have the h allele

Each of us has two alleles for the thumb extension trait. As a result, we only have these combinations.

Homozygous: Having two of the same allele for a trait

Heterozygous: Having two different alleles for a trait

H is dominant (always upper case letter)

h is recessive (always lower case letter)

The dominant allele always wins. (the dominant allele, if it exists, is expressed)

Genotype: The genes of the person

Phenotype: How the genes are expressed

So…

What are the possible genotypes?

Each child receives a set of alleles from the parents. Each child’s allele can be different from his other siblings.

An easier way to see the possible genetic outcomes is with a punnett square

First, you put one parent on the board. You split up the two alleles of the parent and put one at each side.

Then you pull down the allele for each offspring…

Then you put the other parent on the board. You split up the two alleles of the parent and put one at each side.

Then you pull down the allele for each offspring…

Are all traits inherited this simply?

No, thumb extension is a well-defined trait, most traits are more complex and cannot be tracked through generations this easily.

Alleles can work together to produce incomplete dominance.

Gregor Mendel

A priest that first studied heredity from his pea plants in the court yard.

What did he do?

Mendel started with purebred pea plants (all the offspring were the same as the parents) that were tall and short.

Mendel then crossbred the purebred strains of short and tall plants.

This is what he saw with the first generation…

What was odd to Mendel was that the short trait then showed up in the second generation…

Mendel decided that there must be dominant and recessive traits. He made a punnett square to explain the trait inheritance.

Mendel then crossbred the offspring of the 1st generation….

Draw another Punnett to see what the offspring of these two plants will look like.

Mendel’s use of dominant and recessive alleles worked!

Do the punnett square on your worksheet for carnations.

R is dominant , a red flower

r is recessive, a white flower

Rr is incomplete dominance, a pink flower

Do a punnett square for three generations

(you pick which offspring to breed)

Label the phenotypes and genotypes of each offspring