Transcript Mendel and His Peas

Mendel and His Peas
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Objectives
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Explain the difference between
cross and self pollination
Explain the relationship between
traits and heredity
Describe the experiments of
Gregor Mendel
Explain the difference between
dominant and recessive traits
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Heredity is…
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The passing of traits from parent to
offspring, and it is very complicated
Different people have different traits,
such as eye color, hair color, and ear
lobes that do not attach directly to their
head
Where do people get these different
traits?
Many traits are inherited from parents
and passed from parents to offspring
through genes, which are a set of
instructions for an inherited trait
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Gregor Mendel
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Born in 1882 on a farm in Austria
Studied science at a monastery
He discovered the principles of heredity
in the monastery garden. Known as the
Father of Genetics
His research was mostly on plants
He noticed that often a trait appeared in
one generation (parents) and not present
in the next generation (offspring)
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Anther
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Filament
Pistil
Female
Reproduction
organ
A Wild Strawberry Flower
http://www.countrysideinfo
.co.uk/flower.htm
Male
Reproduction
organ
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http://hordeum.oscs.monta
na.edu/home/documents/bb
.jpg
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Pollination
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Transfer of pollen from the anthers
of the stamen to the stigma of the
pistil.
Fertilization
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The union of one egg cell and one
sperm cell.
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Pollination Video Clips
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http://www.fotosearch.com/DGV741/620009/
(Bee on flower)
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http://video.google.com/videoplay?docid=529
4323989667289565 (Importance of Honey
Bees in pollination)
The Pollination Song
http://www.mbgnet.net/bioplants/pollination.html
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Self-Pollinating Peas
Animation of
selfpollination
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http://www.fs
.fed.us/wildfl
owers/pollin
ators/images
/selfpollinati
on.gif
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Mendel wanted to find out more
about patterns that traits take on
from generation to generation
To keep it simple, he focused on
only one kind of organism – peas
Peas are self-pollinating, which
means they have both male and
female reproductive structures
These are true breeding plants
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True Breeding
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All offspring have the same traits
Examples:
True breeding plants with purple
flowers will always produce purple
flowers
True breeding plants with long
stems will always produce plants
with long stems
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Cross-Pollination
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Peas can also cross-pollinate
In cross-pollination pollen from one plant
fertilizes the ovule of a flower on a different plant
This can occur from insect travel or by wind
Cross-Pollination
Animation
http://www.fs.fed.u
s/wildflowers/polli
nators/images/xpol
lination_ani.gif
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Cross-pollination
http://cache.eb.com/eb/image?id=95388&rendTypeId=34
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Cross-Pollination by
man
http://hordeum.os
cs.montana.edu/h
ome/documents/m
ethods1.htm
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Mendel Studied
Characteristics
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A characteristic is a feature that
has different forms in a population.
Examples: hair color, eye color
The different forms of a
characteristic is called a trait .
Examples: red hair, blue eyes
Mendel used peas to mix and
match traits of different
characteristics.
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Mendel’s First
Experiments
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Mendel crossed true
breeding pea plants to study
7 characteristics
The offspring from the cross
of 2 true breeding plants are
called the first generation
plants
In his experiment, one trait
was always present and one
trait seemed to disappear 21
Dominant and
Recessive Traits
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Dominant Trait – the trait that was
always present in the first
generation
Recessive Trait - all other traits
seem to fade into the background,
and are not shown in the first
generation
Dominant and Recessive traits
appear in all organisms
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Mendel’s Second
Experiment
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Mendel allowed first generation
plants to self-pollinate
The recessive trait reappeared in
the second generation.
He did the same with each of the
other 6 characteristics, in each
case the recessive trait
reappeared.
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Ratio’s in Mendel’s
Experiments
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Mendel tried to figure out the ratio of
dominant traits to recessive traits
A ratio is a relationship between 2
numbers that is often expressed as a
fraction (not always – 3:1 or 3 to 1)
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Mendel - Gone But Not
Forgotten
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Each pea plant has 2 sets of
instructions for each characteristic
Each parent would donate 1 set of
instructions
Mendel published his results but it
was 30 years after his death before
he was recognized for his work.
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Traits and Inheritance
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Gene: a set of instructions for a trait.
Gene is made up of 2 or more parts
called alleles. One comes from the
biological mother and one from the
biological father.
Allele: different forms of a gene.
Dominant alleles are written with a
capital letter.
Recessive alleles are written with a
lower case letter.
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Genes
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Chromosomes
are in the
nucleus of the
cell.
Chromosomes
are made up of
DNA.
Genes are a
section of DNA
Alleles are part
of a gene
given to an
organism from
each parent.
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Human Chromosomes
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Female Chromosomes Matched
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Male Chromosomes Matched
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Alleles
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Phenotype
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Is an organism’s
appearance
Written in words
Example: purple
or white flowers
Example: brown
eyes, blue eyes,
hazel eyes.
Green eyes
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Genotype
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Letters that represent the alleles for each trait.
Dominant traits are written with capital letters
Recessive traits are written with lower case letters.
Homozygous: an organism with either 2 Dominant or
2 Recessive allele. True breed.
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Example: TT (Tall plant) tt (short plant)
Heterozygous: an organism with one Dominant allele
and one Recessive allele.
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Example: Tt (Tall plants)
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Punnett Square
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Used to calculate
the possible
outcomes of a
genetic cross.
The alleles from
both parents are
placed
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