Mendel`s Theory
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Transcript Mendel`s Theory
A Theory of Heredity
Alleles
Dominant
Recessive
Homozygous
Heterozygous
Genotype
Phenotype
People believed offspring were a ‘blend’ of their
parents’ traits
But Mendel said each character is either inherited
from the mom or the dad, not a blend of the two
http://history.nih.gov/exhibits/nirenberg/images/photos/01_mendel_pu.jpg
1.
For each inherited character, an individual has two
copies of the gene, one from each parent.
http://www.blackwellpublishing.com/ridley/im
ages/atomistic.jpg
2.
There are alternative versions of genes
Known as Alleles
http://www.csulb.edu/~kmacd/361-6-Ch1_files/allele.jpg
When two different alleles occur together, one of
them may be completely expressed, while the other
may have no observable effect on the organism’s
appearance.
Dominant
Recessive
3.
http://upload.wikimedia.org/wikipedia/commons/thumb/1/17/Punnett_square_mendel_flowers.sv
g/550px-Punnett_square_mendel_flowers.svg.png
4.
When gametes are formed, the alleles for each gene
in an individual separate independently of one
another.
So, each gamete only has one allele for each inherited
characteristic
When fertilized, they contribute one allele.
Letters are used to represent alleles
Dominant alleles are capital letters
Recessive alleles are lower case letters
If a gene has two same alleles, then it is called
homozygous
If a gene has two different alleles, then it is called
heterozygous.
In heterozygous individuals, which gene is expressed?
Dominant or Recessive?
What happens to the allele that is not expressed? Does
it disappear? Why or why not?
Genotype
set of alleles that an individual has for a character.
Phenotype
physical appearance of a character
Name the genotype ant the phenotype of these
flowers.
Alleles
Dominant
Recessive
Homozygous
Heterozygous
Genotype
Phenotype