Transcript Genetics PowerPoint

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