Download Other Patterns of Inheritance

Other Patterns of Inheritance
(Chapter 11.3)
Exceptions to Mendel’s Principles
First, let’s review Mendel’s principles.
Mendel’s Principles
•
The traits that you inherit depend on your
genes (units of inheritance), which came
from your parents.
Mendel’s Principles
•
•
If a gene has two or more alleles (forms)
for a single trait, some alleles may be
dominant and others may be recessive.
This is called simple dominant/recessive
inheritance.
Mendel’s Principles
•
•
In most sexually reproducing organisms,
the organisms has two sets of a gene
(one from each parent) for a trait.
Note that they may not be the same form
of the gene. (Why not?)
Mendel’s Principles
•
•
•
These alleles separate randomly during
gamete formation.
This is Mendel’s law of segregation.
Therefore, a heterozygous parent can
give either the dominant or the recessive
allele to its offspring
Mendel’s Principles
•
•
•
Genes (alleles) for different traits
separate independently during gamete
formation.
This is Mendel’s law of independent
assortment.
Therefore, having one trait does not
necessarily mean that you also have
another trait.
These principles can also be referred to as
the principles of “Mendelian genetics.”
Next up, “non-Mendelian genetics”
In other words, exceptions to the “rule”.
Some alleles are neither dominant
nor recessive.
Incomplete dominance:
• example – flower color in snapdragon
plants (3 phenotypes: red, white and pink)
• Which is the phenotype of the
heterozygote?
• How would you write the genotypes?
Some alleles are neither dominant
nor recessive.
Codominance:
• example – feather color in some chickens
(3 phenotypes: black, white and blackand-white)
• Which is the phenotype of the
heterozygote?
• How would you write the genotypes?
Some genes have more than two
alleles.
Multiple Alleles:
• example – human blood type has three
alleles (A, B, and O), which results in four
different phenotypes (Types A, B, AB, and O)
• How many alleles would each individual
have?
• Which is the phenotype of the heterozygote?
• How would you write the genotypes?
Some traits are controlled by more
than one gene.
Polygenic traits:
• example – three genes affect eye color in
fruit flies; four (or more) genes affect human
skin color
• Example - HLA (human leukocyte antigen)
system that recognizes foreign tissue in
humans – because many alleles contribute to
the phenotypes, there are many possible
phenotypes (30 million for the HLA system!).
Discuss:
1. How many phenotypes would you
expect to see in a case of simple
dominant/recessive inheritance?
2. Codominance?
3. Incomplete dominance?
4. Multiple allelic inheritance?
5. Polygenic inheritance?
Genes and the Environment
Phenotype does not depend entirely on
genotype.
Environmental conditions can affect gene
expression and influence genetically
determined traits.
example – the western white butterfly:
wing color depends on when they
hatch (because of temp differences)