Download Genetics

Genetics
• Genetics is defined as
the scientific study of
heredity
• Gregor Mendel is
considered to be the
father of modern genetics
Genetics
• Mendel’s experiments revealed the following that
we use as the foundation for modern genetics
– Genes are the chemical factors that determine traits
– Alleles are different forms of a gene
• And that some alleles are dominant and some are recessive
• Also, you will need to know the following terms
– Genotype refers to the genetic sequence of an organism
– Phenotype refers to an observable characteristic of an
organism
Genetics
• Mendel studied the traits of pea plants and
controlled their fertilization
– In other words, he determined which plants would
breed and studied their “offspring”
Parent Generation
Filial 1 (First)
Generation
Filial 2 (Second)
Generation
Genes and Alleles
Think of genes as being
specific DNA sequences
that code for particular
triats or characteristics
of an organism
For example, one
“gene” can code for eye
color while another
“gene” codes for hair
color
Genes and Alleles
Think of alleles as
different types of
“genes”.
For example, one
“allele” codes for brown
eyes while another for
green.
Or on another “gene”,
one “allele” codes for
black hair while another
“allele” codes for blonde
hair.
Dominant/Recessive Alleles
• Mendel also discovered the concept of dominant
and recessive alleles
– The principal of dominance states that some alleles are dominant while some
alleles are recessive
– In general, dominant alleles will be expressed over recessive alleles
– However, note some alleles are not as clear cut as “dominant” and “recessive”
and if time permits, we will talk about these traits
• With Mendel’s pea plants, he discovered the
following regarding their flower color
The violet flower color “symbolized” as “B” is
dominant
The white flower color “symbolized” as “b” is
recessive
Dominant/Recessive Alleles
• Alleles are found in pairs, with the dominant allele,
if present, expressing themselves over recessive
alleles
Therefore, for the flower color alleles [B] and [b], what are the
possible combinations?
Combination
Description
BB
This combination is also known as homozygous (the
same allele) and will yield the color…
Bb
This combination is also known as heterozygous (one
dominant and one recessive) and will yield the color…
bb
This combination is also known as homozygous, and
will yield the color…
Flower Color
Mendel’s Law of Segregation
• Gametes are known as the sex cells of an organism
and in higher organisms, usually the sperm and the
egg
• Each gamete receives only one copy of an
allele
• As a result, alleles separate independently from
one another (theorized by Mendel)
• When organisms form sex cells, only half of the
DNA ends up in a gamete (we’ll talk about this
during meiosis)
Mendel’s Law of Segregation
Punnet Squares
• Mendel’s Law of Segregation allow us to use Punnet
Squares to predict an offspring’s phenotype
• Setup for predictions of one allele, also known as a
monohyrbird cross is as follows
Start by drawing out a
2x2 grid
Punnet Squares
• Now suppose we fertilized two heterozygous, violet pea
plants. What would their offspring look like?
Bb
Bb
And the genotype
of the other parent
here…
After drawing your grid,
write one genotype of your
parent here…
Punnet Squares
• Now suppose we fertilized two heterozygous, violet pea
plants. What could their offspring look like?
Bb
B
B
Bb
b
b
Next, “independently assort”
your gametes (i.e. break
them apart)
Punnet Squares
• Now suppose we fertilized two heterozygous, violet pea
plants. What could their offspring look like?
Bb
B
b
B
BB
Bb
b
Bb
bb
Bb
Then “cross” the gametes in
the box! (You can erase the
genotypes of the parents
now too!)
Punnet Squares
• Now suppose we fertilized two heterozygous, violet pea
plants. What could their offspring look like?
Finally, predict what you will
have!
B
B
b
BB
Bb
b
Bb
bb
Genotype Breakdown
1x BB (Violet) [25%]
2x Bb (Violet) [50%]
1x bb (White) [25%]
Phenotype Breakdown
3x Violet [75%]
1x White [25%]
Punnet Squares
• Now suppose we fertilized a homozygous recessive
white plant with a heterozygous, violet pea plant. What
would their offspring look like?
bb
Bb
And the genotype
of the other parent
here…
After drawing your grid,
write one genotype of your
parent here…
Punnet Squares
• Now suppose we fertilized a homozygous recessive
white plant with a heterozygous, violet pea plant. What
would their offspring look like?
Next, “independently assort”
bb
b
B
Bb
b
b
your gametes (i.e. break
them apart)
Punnet Squares
• Now suppose we fertilized a homozygous recessive
white plant with a heterozygous, violet pea plant. What
would their offspring look like?
Then “cross” the gametes in
bb
b
b
B
Bb
Bb
b
bb
bb
Bb
the box! (You can erase the
genotypes of the parents
now too!)
Punnet Squares
• Now suppose we fertilized two heterozygous, violet pea
plants. What could their offspring look like?
Finally, predict what you will
have!
b
B
b
Bb
bb
b
Bb
Genotype Breakdown
2x Bb (Violet) [50%]
2x bb (White) [50%]
bb
Phenotype Breakdown
2x Violet [50%]
2x White [50%]