Transcript Genes and Inheritance

Genes and
Inheritance
What is DNA?
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Chromosomes are made
up of DNA coiled tightly
around proteins called
histones.
Deoxyribonucleic Acid
(DNA) carries the code
that tells cells what to do.
DNA Structure
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DNA is made up of nucleotides.
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Each Nucleotide is made up of 3 parts;
Phosphate group
 Nitrogenous base
 Pentose sugar
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These nucleotides are
arranged in long
strands that pair up to
form a ladder.
This ladder then
twists to form what is
called a double helix.
Base Pairing
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There are 4 nitrogenous bases.
Adenine
 Thymine
 Cytosine
 Guanine
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Each of these bases can only pair with
one other base.
Adenine always pairs with thymine
 Cytosine always pairs with guanine
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So, what?
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The order in which these base pairs are
found on different sections of DNA
determine everything about you!
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Our information is organized into genes
(like documents), which are organized into
chromosomes (files in a filing cabinet)
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The combination of our genes makes all of
us unique
Gregor Mendel and
Genetics
Who’s this guy?
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Gregor Mendel was
an Austrian monk
who worked with pea
plants.
Mendel worked with
pea plants to study
heredity.
Why pea plants?
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The four main reasons Mendel worked
with pea plants were:
The common pea plant was available throughout
Europe
 It is easy to grow and matures quickly
 Pea plants self – pollinate, allowing Mendel to
control which plants reproduced
 Different varieties of pea plants have different traits
that can be easily observed from one generation to
the next.
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Mendel’s Experiment
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The first thing Mendel needed to do was
obtain purebred plants for the traits he
wanted to study.
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A purebred organism results from many
generations of selective breeding.
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Plant height was one of
the traits Mendel used in
his studies of the pea
plant.
Once he had a purebred
short and a purebred tall
plant he would cross –
pollinate them and
observe the results.
Mendel called this
purebred cross the parent
or P generation.
The Results
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The offspring of the P generation were
called the F1 generation.
What do you think they looked like?
These pea plants were all tall.
Mendel then cross – pollinated these
plants with each other and created the F2
generation.
What do you think they looked like?
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These plants were 75% tall and 25%
short.
The Principle of Dominance
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These results led Mendel to conclude that
the tall trait was dominant and the short
trait was recessive.
A dominant trait is a characteristic that is
always expressed.
A recessive trait is a characteristic not
usually expressed.
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The presence of the recessive trait in the
F2 generation led Mendel to conclude that
inherited traits are controlled by two
“factors”.
These “factors” segregate in gametes,
only one in each gamete.
Today we know that these factors are
genes. The two forms of a gene are called
alleles.
Law of Segregation
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The law of segregation states that every
individual possess a pair of genes and that each
parent passes a randomly selected copy of only
one of these to its offspring
Since there is no decision in choosing which
gene gets chosen, the Law of Independent
Assortment was also established
Independent Assortment
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States that separate traits are passed
independently of one another from parent to
offspring
That is, the biological selection of a particular
gene pair for one trait to be passed to the
offspring has nothing to do with the selection of
the gene for any other trait
Alleles of different genes assort independently
of one another during gamete formation