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MENDEL’S WORKKey Concepts
What were the results of Mendel’s experiments or crosses?
What controls the inheritance of traits in organisms?
Key Terms
Heredity Trait Genetics Fertilization Purebred
Gene Alleles Dominant allele Recessive allele hybrid
Mendel’s Work Mendel experimented with thousands
of Pea plants looking at their different traits to understand the process of heredity. His discoveries form the foundation of genetics.
Heredity –the passing of physical characteristics from parents to
offspring Trait- each different form of a
characteristic Genetics – the study of heredity
Mendel’s Experiments
Flowering Plant anatomy Pistil – produces the female sex cells or eggs Stamens – produce pollen which contains
the male sec cells or sperm Fertilization is when the egg and sperm join
forming a new organism In plants the pollen must reach the pistil for
fertilization to occur. This is called pollination
Pollination
Pea plants usually self-pollinate. The pollen from their stamens lands of the same plants pistils.
Mendel developed a method to cross-pollinate pea plants. He took pollen from one pea plant and brushed it onto the pistil of another.
Crossing Pea Plants
Mendel crossed plants with contrasting traits
Ex. Tall plants with short plants
Started with purebred plants – a purebred organism is one who is the offspring of many generations of that have the same trait
The F1 Offspring
Mendel crossed purebred tall with purebred short Parental (P) generation
Tall x short Offspring from the cross are called F1
(filial) All F1 offspring were tall
F2 offspring
When F1 were full grown, Mendel allowed them to self-pollinate
F2 were a mix of tall and short
¾ were tall and ¼ were short
Experiments with OtherTraits
Mendel crossed pea plants with other contrasting traits such as seed shape, seed color, seed coat color, etc.
In all crosses the F1 generation had only 1 form of the trait
In the F2 generation the “lost” form reappeared in ¼ of the plants.
Dominant and Recessive Alleles Mendel’s Conclusion factors control the
inheritance of traits in peas. They exist in pairs The female parent
contributes one factor and the male parent contributes the other factor
One factor in a pair can mask or hide the other factor
Genes and Alleles Genes – factors that control a trait Alleles – different forms of a gene An organisms traits are controlled by the
alleles it inherits from its parents. Some alleles are dominant, while others
are recessive Dominant allele – trait always shows Recessive allele –trait is hidden whenever
dominant allele is present
Alleles in Mendel’s Crosses
Stem Height Cross P generation tall tall x short short F1 generation all were tall short- Look
tall F2 generation ¼ tall tall - look tall ¼ tall short + ¼ short tall
– look tall ¼ short short – look
short
Symbols for alleles
Letters are used to represent alleles
Capital letters are used for dominant alleles
Lowercase letters are used for recessive alleles
Purebred tall = TT Purebred short = tt Hybrid (one of each) =Tt
Significance of Mendel’s Contribution Before Mendel most people thought that the
traits of an individual were a blend of their 2 parents.
If they blended the Tt plants should be medium height
Mendel found out that traits are determined by individual alleles some of which are dominant and some recessive.
Recessive traits may seem to disappear in the offspring only to reappear in the next generation
Mendel’s work was not recognized during his lifetime, but was rediscovered in 1900. He is now
considered the Father of Genetics.
Sources
http://kentsimmons.uwinnipeg.ca/cm1504/mendel.htm http://www.exploringnature.org/db/detail.php?dbID=45&detID=22
90 http://ncse.com/files/images/pea_plant.preview.jpg http://library.thinkquest.org/28751/review/plants/6.html http://www.cactus-art.biz/note-book/Dictionary/Dictionary_C/dictio
nary_cross_pollination.htm http://academic.kellogg.edu/herbrandsonc/bio111/genetics.htm http://www.bioinformatics.nl/webportal/background/
mendelinfo.html http://www.absoluteastronomy.com/topics/
Experiments_on_Plant_Hybridization http://www.csulb.edu/~kmacd/361-6-Ch2.htm http://library.thinkquest.org/17109/tutorial.htm http://www.learner.org/interactives/dna/genetics3.html http://cynthialeitichsmith.blogspot.com/2010/06/guest-post-
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