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Introduction to genetics
• Biology chapter 11
• Mr. Hines
• 11.1 The work of Gregor Mendel
What makes you unique?
A. Nearly all living things are unique in some way.
B. Humans for example all have different facial
features that can be easily recognized by friends
and family.
C. Traits – specific characteristics that vary from one
organism to another – example – eye color, hair
color, height, intelligence, shape of ears, etc..
D.
Traits
Take a minute to write down 5 of
your best traits.
Inheritance – the genes that you get from your parents that determines your traits – example eye color from mom, hair color from dad.
What is genetics? The scientific study of heredity
What is heredity? The scientific study of inheritance – huh? Inheritance and heredity are the same thing
In other words, genetics is the study of how 2 parents can create offspring that will be similar to both parents, but not quite like either parent.
You are a mix between mom and dad, but you are different from them both – genetics
Checkpoint:
• What is a trait?
__________________________________
• What is genetics?
__________________________________
Gregor Mendel’s Peas
Inheritance is not limited to humans and is found in all forms of life.
Gregor Mendel was and Austrian monk who led the way to understanding genetics with his work with pea plants.
He was in charge of the garden in his Monastery – there he studied plants and his discoveries changed biology forever.
He discovered that sexual fertilization in
plants was done with 2 separate parts of a
plant – the flower.
Here are the basic parts of a flower.
1. Stamen (male part) carries pollen (sperm)
2. Pistil (female part) carries ovule (egg)
Basic flower parts review
When pollen (sperm) makes contact with the
ovule (egg), fertilization occurs.
Fertilization – process in sexual reproduction
in which male and female reproductive
cells join to form a new cell.
Many plants such as peas have flowers that
can fertilize themselves – self pollination.
This means that one plant acts as both
parents.
In the case of self pollination, the offspring
will look just like the parent
The traits will be the same.
Self pollination is similar to you mating with
you – the offspring would be --- you.
If you fertilized yourself and had children,
your children would be identical copies of
you.
Mendall based his experiments from plants
that were self pollinated.
Offspring – new life that forms after fertilization – You are the offspring of your parents
Mendel knew that if he were to study genetics, self pollination could not be permitted.
Self pollination and true breeding are the same thing.
In order to all study genetics, he had see
fertilization of 2 different plants(2
different parents)
He did this by cutting off the pollen bearing
male parts (stamens) of the pea flowers
and pollinated them from other pea plants.
Checkpoint
What part of the flower hold the sperm?
_________________
What part of the flower holds the egg?
__________________
How did Mendell avoid self pollination in pea
plants? _________________
Genes and Dominance Mendel studied 7 different pea plant traits.
Each trait had 2 contrasting characters – such
as seed color – seed color could be green
or yellow.
In order to study genetics, he crossed (mated)
plants with contrasting traits. For
example, he crossed plants that had green
seeds with plants that had yellow seeds.
P Generation F1 Generation F2 Generation
Tall Short Tall Tall Tall Tall Tall Short
Section 11-1
Principles of Dominance
P Generation F1 Generation F2 Generation
Tall Short Tall Tall Tall Tall Tall Short
Section 11-1
Principles of Dominance
P Generation F1 Generation F2 Generation
Tall Short Tall Tall Tall Tall Tall Short
Section 11-1
Principles of Dominance
D. When you cross (mate) parents with
different traits, the offspring are called
hybrids.
E. Hybrid – offspring of crosses between
parents with different traits. For example
– if you mate a black cat with a white cat,
the offspring (kitten) is called a hybrid.
Even if the kitten from this cross comes out
black, it is still a hybrid (because of its
black and white parents)
F. Important notation to learn – page
264
1. P stands for parents
2. F1 stands for first generation of offspring
3. F2 stands for second generation of
offspring
G. So what happens when you cross a plant
with yellow seeds with a plant of green
seeds? (P generation) What will the
offspring have? (F1 generation)
H. Mendel noticed that the offspring had only
one trait from one parent – the other trait
from the other parent seemed to disappear.
For example – when yellow seeds were
crossed with green seeds, the offspring all
had yellow seeds.
Yellow seed x Green seed
Mendel concluded that inherited traits are
passed from one generation to the next.
Today, we say that these inherited traits come
from genes.
Gene – Sequence of DNA that codes for a
protein and thus determines a trait
In other words, a gene is a segment of DNA,
which is found on a Chromosome.
Chromosomes are made of many genes.
So right now we are speaking of 1 gene that
controls seed color.
There are 2 variations of that gene – one
variation of this gene is for yellow seed
and the other variation is for green seed.
We call the different variations of a single
gene an allele.
Allele – one of a different number of forms of
a gene.
For example – eye color is a gene. There are
3 basic alleles for the eye color gene –
green eyes, blue eyes, and brown eyes.
CHECK POINT
What does it mean to cross 2 parent pea
plants? ____________________
What is a hybrid?
_______________________________
What is a gene?
_________________________________
What is an allele? ___________________
IV. Gene dominance
A. Another conclusion from Mendel is that
some alleles are dominant and some are
recessive.
B. Dominant – Overpowering, expressive
C. Recessive – Overpowered, unexpressive
D. Example – when a pea plant with green
seeds was crossed with another pea plant
with yellow seeds, the offspring all had
yellow seeds. This shows that the gene
for the yellow seed is dominant and the
gene for the green seed is recessive.
E. The only time that a trait of a recessive
allele will show up in the offspring is
when there is no dominant gene to
overpower it.
Check point
What is a dominant allele? ______________
What is a recessive allele? _____________
What happens when a dominant and a
recessive allele are both present during a
crossing? _____________________
V. Segregation
A. So what happened to the recessive allele? Did it just disappear, or is it still hanging around somewhere?
B. In order to find out, Mendel crossed the F1 generation of pea plants.
C. When the F1 generation has been successfully mated, the new offspring are called the F2 generation. The F2 generation are the grandchildren of the P generation
D. Mendel noticed that when the F2
generation grew up, the recessive alleles
reappeared. In other words, the green
seeds were back. How can this be?
E. Mendel concluded that during the mating
process, the allele for each trait must be
somehow separated from each other.
F. This could be explained in gametes.
G. Gamete – specialized cell involved in
sexual reproduction. (sperm cells (male)
and egg cells (female) are gametes.)
• H. Key point – When each F1 plant
flowers and produces gametes, the two
alleles segregate from each other so that
each gamete carries only a single copy of
each gene. Therefore, each F1 plant
produces two types of gametes – those
with the allele for yellow seed and the
allele for green seed.
Self pollination