Exploring Mendelian Genetics

1
Exploring Mendelian Genetics

• Chapter 11, Section 3

2
The Complexity of Inheritance

• Mendel studied simple characteristics in pea
  plants and was able to define some basic
  principles behind their inheritance patterns
• However, many characteristics visible in
  organisms have more complex inheritance patterns
  than those studied by Mendel

3
Incomplete Dominance
r r
w rw Pink rw Pink
w rw Pink rw Pink

• Neither allele is dominant over the other,
  therefore the heterozygous phenotype is an
  intermediate (or BLEND) of the two homozygous
  phenotypes

4
Codominance
R R
W RW Roan RW Roan
W RW Roan RW Roan

• Both alleles are visible in the heterozygous
  phenotype
• Ex Roan Coat (both red and white hairs)
• AB blood (both A and B antigens)

5
Multiple Alleles
Phenotype Genotype
A IAIA, IAi
B IBIB, IBi
AB IAIB
O ii

• When there are more than 2 alleles in the
  population
• Ex Blood Type (IA, IB, i)
• Coat color in Rabbits
• (C, cch, ch, c)

6
Polygenic Inheritance

• When two or more genes control the trait
• The more genes that control the trait, the more
  variation in phenotypes
• Ex Height, eye color, skin color in humans
• Feather color in parakeets

Green Blue Yellow White
BBYY BByy bbYY bbyy
BbYY Bbyy bbYy
BBYy
BbYy
7
The Environmental Influence

• Environmental factors (such as temperature, sun
  exposure, altitude, diet, exercise, etc.) can
  have significant effects on the phenotypes of
  certain organisms
• In general, the product of a genotype is not
  typically a defined phenotype, but rather a range
  of possibilities influenced by the environment.