Transcript ppt

Inheritance and Genetics
Gregor Mendel
• Studied the garden pea
• studied height, flower color, seed coat color,
and seed shape over many generations
• he chose 1 or 2 traits per generation to
• crossed plants with different traits and
learned that offspring usually had dominate
• Mendel found that the inheritance of traits
was not due to blending but instead specific
traits or units of inheritance were passed
from generation to generation
• we call those units of inheritance genes
• No matter what trait he selected for the
second generation would show traits at a
ratio of 3 to 1 (3 dominate for everyone
• From this he deduced the presence of genes
and alleles
• Homozygous- same allele
• Heterozygous - different allele
• Alleles - alternate forms of the same trait or
• similar genes are arranged in a similar orger
in a chromosome, the location is called a
• since 2 alternate forms are present we
describe them with capital (dominant) and
lower case (recessive) letters
• In a homologous pair a dominant allele
masks the presence of a recessive allele
Homozygous with dominant
Homozygous with recessive
Heterozygous ?
Genotype refers to the genetic makeup of an
• Phenotype refers to the actual expression of
the genetic makeup
Mendel’s Principles of Inheritance
• Inherited traits are transmitted by genes which
occur in alternate forms called alleles
• Principle of Dominance - when 2 forms of the
same gene are present the dominant allele is
• Principle of Segregation - in meiosis two alleles
separate so that each gamete receives only one
form of the gene
• Principle of Independent Assortment - each trait is
inherited independent of other traits (chance)
Punnett’s Square
• Draw a Punnett square for 2 genes
• Use Bb for hair color and Ee for eye color