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Objectives
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…
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
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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A Wild Strawberry Flower
http://www.countrysideinfo.co.uk/flower.htm
Anther
Filament
Pistil
Female Reproduction organ
Male Reproduction organ
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2
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Pollination
Transfer of pollen from the anthers of the stamen to the stigma of the pistil.
Fertilization The union of one egg cell and one
sperm cell.
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Pollination Video Clips
http://www.fotosearch.com/DGV741/620009/ (Bee on flower)
http://video.google.com/videoplay?docid=5294323989667289565 (Importance of Honey Bees in pollination)
The Pollination Song
http://www.mbgnet.net/bioplants/pollination.html
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Self-Pollinating Peas
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
Animation of self-pollination
http://www.fs.fed.us/wildflowers/pollinators/images/selfpollination.gif
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True Breeding
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 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.us/wildflowers/pollinators/images/xpollination_ani.gif
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Mendel Studied Characteristics 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
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
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Dominant and Recessive Traits 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 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
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 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
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
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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Phenotype
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
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. Example: TT (Tall plant) tt (short plant)
Heterozygous: an organism with one Dominant allele and one Recessive allele. Example: Tt (Tall plants)