Transcript genetics kaht 2012

Genetics!
Heredity is the
passing of traits from
parent to offspring.
These traits are
controlled by genes.
Traits are observable characteristics
we inherit from our parents
Genes are found on chromosomes. They
are sections of the DNA.
When pairs of chromosomes separate into
sex cells during meiosis, pairs of genes
also separate from one another.
As a result, each sex cell ends up with one
form of a gene for each trait that an
organism shows.
The different forms a gene may have for a
trait are its alleles.
Example:
straight or widow’s peak
are the alleles for hairline.
Gregor Mendel (1822-1884). Mendel is
considered the father of genetics..
Mendel conducted the first studies on how traits
pass from one generation to the next.
He worked with pea plants
Mendel’s Experiments:
Mendel chose to experiment with peas because they possessed
four important qualities:
1. Peas are true-breeding (all offspring will have the same
characteristic generation after generation).
2. (purple vs. white flowers; round vs. wrinkled seeds).
3. Peas reproduce by self-pollination, in which pollen produced
by a flower fertilizes eggs in the same flower.
4. Pea plants grow quickly and do not require much space.
There are 7 Different Traits to Consider With Peas:
1. Pea shape (round or wrinkled)
2. Pea color (green or yellow)
3. Pod shape (constricted or inflated)
4. Pod color (green or yellow)
5. Flower color (purple or white)
6. Plant size (tall or dwarf)
7. Position of flowers (axial or terminal)
The dominant allele is
the form of a trait that
appears to dominate or
mask another form of
the same trait.
The recessive allele is the
form of the trait that seems
to disappear in a
population but can
reappear depending on the
way the alleles combine.
An organism that always
produces the same traits
in its offspring is called a
purebred. (purebred tall,
purebred short)
Probability is a form of mathematics that
helps predict the chance that something will
happen.
Mendel’s experiment utilized this.
To predict what the offspring will look like
without actually making the cross, scientists
use Punnett squares.
1) Capital letter stands for a dominant allele
2) Lower case letter stands for recessive allele
Every trait has two alleles- this is the genotype!
Ex)
TT
(homozygous)
Tt
(heterozygous)
tT
(heterozygous)
tt
(homozygous)
The physical trait that shows as a result of a
particular genotype is its phenotype.
In a Punnett Square, the letters
representing the two alleles from one
parent are written along the top and those
of the second parent on the side.
Each section of the square is filled in like a
multiplication problem with one allele
donated from each parent.
The letters that fill in each inside square
represent the POSSIBLE genotypes of
offspring those parents could produce.
T = Tall pea plant
t = Short pea plant