Download Genetics - The Basics

Genetics - The Basics
Once Upon a Time…
...there was a monk named Gregor Mendel.
Once Upon a Time…
Mendel was a monk that lived in Austria in the mid19th century.
While living in a monastery in Brno he grew many
different generations of pea plants and recorded his
observations from these generations
He looked at many characteristics like flower colour
and pea shape and pea colour.
Once Upon a Time…
He referred to the parent generation (the start) as P
The generation that came after that was then known as
F1 generation
The generation that came after F1 was then named F2
and so on and so forth
Once Upon a Time…
Mendel used the pea because the physical traits they
were showing came in two forms so they were easier to
track and to analyze
He also used the pea plants because they were easy to
manipulate and create more of - they use selfpollination reproductive strategies
Once Upon a Time…
Mendel, as many scientists in history, died before his
work became recognized in the scientific world but
today we use his research and discoveries as the basis
for many genetic research
When looking at basic laws of inheritance and basic
traits we are studying Mendelian genetics and looking
at Mendelian traits
World Dominance-ation...
When Mendel used pollen from the pea plant with
round seeds to fertilized a pea plant with wrinkled
seeds, he found that all the offspring (progeny) had
round seeds
He didn’t stop there, he then used a plant with wrinkled
seeds to pollinate one with round seeds and again
found that all the offspring had round seeds
World Dominance-ation...
This experiment showed that the round seeds were the
dominant trait, regardless of parentage. This meant
that if the dominant allele is present in a chromosome,
this is the trait that you will see
Recessiveness and Alleles
The other gene that is not being expressed physically is
then called the recessive trait.
With this knowledge, Mendel realized that there must
be ways for there to be two or more different forms of
‘factors’ (genes) that give rise to different traits
These different forms are called alleles
Dominant vs. Recessive
When looking at the dominant alleles, we write it as a
capital letter
Example: dominant allele for seed shape is round
therefore we would represent it with a capital R
When looking at the recessive alleles, we write it as a
lowercase letter
Example: recessive allele for seed shape is wrinkled
therefore we would represent it with a lowercase r
Principle of Segregation
Mendel’s research began to focus on the dominant and
recessive traits expressed by the pea plants
When he crossed pure round seed plants with pure
wrinkled plants, 100% of the F1 generation had round
seeds
He was astonished to find that 25% of the F2
generation of these seeds had wrinkled seeds!
Principle of Segregation
He performed multiple tests with the same plants and found that
for the F2 generation he continued to get the same 3:1 ratio (75 %
round to 25% wrinkled)
To explain this, Mendel stated that each seed had 2 copies (alleles)
of each gene that can be the same or different
A round seed must always carry at least one R allele but wrinkled
seeds must always carry two r alleles (rr)
Principle of Segregation
When two alleles are the same and paired together,
they are called homozygous
When the alleles are different, and paired together,
they are called heterozygous
The genes that are expressed are called genotype
The physical appearance is called phenotype
Principle of Segregation
Mendel also said that two copies of a gene undergo
segregation during meiosis (separation of the alleles)
Questions
page 600
#1, 2, 5