Transcript Heredity Mendel and His Peas

Heredity
Mendel and His Peas
Biology
First, Let’s Review!
Sexual Reproduction
Process of a sperm fertilizing an egg
Gametes
Sex cells (eggs, sperm)
Meiosis Review
Meiosis
Cell division that results in haploid sex
cells
Number of chromosomes in somatic
(body) cells= 46
These are diploid cells!
Number of chromosomes in gametes
(sex cells)= 23
These are haploid cells!
What is Heredity?
Heredity is the passing of traits from
parents to offspring.
Hair color, eye color, height, etc.
But sometimes both parents will have
brown eyes, but their child has blue
eyes.
Who was Gregor Mendel?
Mendel was born in 1822 in Austria.
He grew up on a farm and knew a lot
about cultivating flowers and fruit.
He became a monk and started to work
in the monastery garden.
He noticed that certain traits were
passed from parent plants to offspring
plants.
A Mystery
Mendel knew that sometimes the
patterns of inheritance seemed simple
and sometimes they were not.
Sometimes a trait that appeared in one
generation did not show up in any of
the offspring in the next generation, but
suddenly the trait would appear again
in the third generation.
Mendel’s Peas
Mendel chose peas to conduct his
experiments with.
Peas grow fast, can self-pollinate, and
they come in many different varieties.
A self-pollinating plant contains both
male and female reproductive
structures.
More Peas
Mendel chose to study only one
characteristic at a time, such as color,
height, or shape.
Mendel chose plants that had two
forms for each of the characteristics he
wanted to study. Ex: yellow and green
peas.
True-Breeding Plants
When a true-breeding plant selfpollinates, it will always produce
offspring with the same trait the parent
plant has.
For example: Green pea plants will
always produce green pea offspring.
Cross-Pollination
Mendel wanted to find out what would
happen if he bred two plants with
different characteristics.
In cross-pollination, the anthers of one
plant are removed so the plant cannot
self-pollinate. Then pollen from another
plant is used to fertilize the plant
without anthers.
Mendel’s First Experiment
Mendel crossed plants that had round
peas with plants that had wrinkled
seeds.
The offspring from this first cross are
known as the first generation.
What do you think the offspring looked
like?
Dominant Vs. Recessive
One trait always appeared (round) and
one trait always disappeared (wrinkled).
Mendel called the trait that always
appeared the dominant trait.
The trait that disappeared is called the
recessive trait.
Mendel’s Second Experiment
Mendel then let the first generation
plants self-pollinate.
The offspring of the first generation are
called the second generation.
What do you think happened?
The wrinkled seeds appeared again!
Mendel’s Results
Mendel decided to count the number of
plants with each trait that turned up in
the second generation.
Mendel noticed that there were patterns
and ratios to how the traits showed up.
Genes and Alleles
Mendel realized that each plant had
two sets of instructions for each
characteristic.
Each parent donates one set of
instructions, called genes, to the
offspring.
The two genes that determine a
characteristic are known as alleles.
The Punnet Square
A Punnet square is used to see all the
possible combinations of alleles from
the parents.
Dominant alleles are symbolized with
capital letters.
Recessive alleles are symbolized with
lowercase letters.
Genotype
The inherited combination of alleles is
known as the offspring’s genotype.
Phenotype
An organism’s actual appearance is
known as phenotype.
Probability
The mathematical chance that an event
will occur is known as probability.
Usually expressed as a fraction, ratio or
percentage.
We use this mathematical method to
calculate genotype probability.
Let’s Try One!
Blue eyes