Mendel and His Peas

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Mendel and His Peas

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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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http://hordeum.oscs.montana.edu/home/documents/bb.jpg

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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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Cross-pollination

http://cache.eb.com/eb/image?id=95388&rendTypeId=34

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Cross-Pollination by man

http://hordeum.oscs.montana.edu/home/documents/methods1.htm

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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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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

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)

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Punnett Square

Used to calculate the possible outcomes of a genetic cross.

The alleles from both parents are placed