Download Genetics - MWMS HW Wiki

Genetics!!!
It’s All Relative…
Gregor Mendel’s Work
• He was a monk who studied pea plants for
insights into heredity
• His studies helped form the foundation for
the modern understanding of genetics
Some Important Terms
• Heredity: the passing of physical
characteristics (or traits) from parents to
offspring.
• Traits: are the different forms of a
physical characteristics like eye color.
• Genetics: the scientific study of heredity.
His Experiments
• Mendel started his experiments using
purebred plants. A purebreed is an organism
which always has offspring demonstrating
same form of a trait as the parent.
• In his first experiment he crossed purebred
tall plants with purebred short plants. The
parent plants he called the parental
generation or P Generation.
Experiments cont…
• He called the offspring from that cross the first
filial (latin for son) or F1 Generation.
• He found these offspring were always tall. Even
though one of the parents was short, this trait seemed
to disappear their offspring.
• He allowed these to grow and reproduce. Their
offspring (which he called the second filial generation)
or F2 Generation had both tall and short members:
about 3/4th were tall and 1/4th were short. In other
words the “lost” trait reappeared in a quarter of the
plants.
Experiment’s cont…
• Mendel repeated these experiments with
several other traits (seed shape, color, pod
shape, and pod color) and found the same
results.
• From his results, he concluded an individual
factor controlled the inheritance of traits
which we now call Genes. These exist in
pairs: one is contributed by the father, one by
the mother.
Genes
• Alleles: these are the different forms of
a gene
• each plant receives a combination of
two alleles from its parents, either two
alleles for tall stems, two for short
stems, or one of each.
Alleles
• Individual alleles control the inheritance of
traits. Some are dominant and some are
recessive.
• Dominant Alleles: always show up and are
expressed as a capital letter:Tt.
• Recessive Alleles: gets masked when a
dominant allele is present and is expressed
as a lower case letter:Tt.
Alleles cont…
• Different letters are used for different traits for
example, T is used for stem height.
• TT- tall (purebred)
• Tt - tall (hybrid)
• tt - short (purebred)
• Hybrids: this organism has two different alleles
for a trait: Tt
• Purebred: the organism has the same alleles:
TT or tt.