Download 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