1. More Complicated Patterns of Inheritance
Biology 1-3c
More Complicated Patterns of Inheritance

2. Rules of Inheritance Any guesses on what these terms mean?
Some traits follow the simple rules of Mendelian inheritance of dominant and recessive genes
Complex traits follow different patterns of inheritance that may involve multiple genes and other factors. For example:
Incomplete dominance
Codominance
Multiple alleles
Gene interaction
Sex-linked inheritance
Any guesses on what these terms mean?

3. Complete Dominance
Complete Dominance results in a phenotype that is a representation of the dominant trait in a heterozygous allele pair.
Red flower x blue flower  Red flower

4. Complete Dominance
This is classic Mendelian inheritance.
More complex patterns exist!

5. Incomplete Dominance
Incomplete Dominance results in a phenotype that is a blend of a heterozygous allele pair.
Red flower x blue flower  purple flower

6. Incomplete Dominance
If black and yellow coat colour exhibit incomplete dominance in dogs and a litter of puppies is born with the following genotypes, what colour will they be?
BB =
YY =
BY =

7. Codominance
Codominance results in a phenotype that shows both traits of an allele pair.
Red flower x blue flower  Red & blue spotted flower

8. Codominance
If black and white coat colour exhibit codominance in dogs and a litter of puppies is born with the following genotypes, what colour will they be?
BB =
WW =
BW =

9. Are the offspring exhibiting incomplete dominance or co-dominance?

10. Assignment: Incomplete & Co-Dominance Worksheet
In partners, please complete the “Create-a-Being” Assignment. (you will share a parent information card but you will both fill out your own booklet)

11. Multiple Alleles
Traits controlled by multiple alleles have more than 2 variations.
Ex. Human blood type has 3 different allele variants, A, B and O
A and B are Codominant to each other and both are Dominant over O
Genotypes
Phenotypes
AA, AO
A blood type AB
AB blood type
BB, BO
B blood type OO
O blood type

12. Multiple Alleles – Human Blood Type
If parents have A (AO) and B (BB) blood types, what are the possible genotypes and phenotypes of their children?

13. Multiple Alleles – Human Blood Type
A mother with blood type A (AO) gives birth to a baby with blood type B (BO). The “father” is blood type AB. Could the child be his? Is this test 100% conclusive?

14. Sex-Linked Traits
Henry the VIII was a British Monarch who was desperate for an heir
He had 6 wives, blaming them for his lack of sons.
He did finally have one son

15. Question: Who is responsible for a babies gender? The mom? The dad?
Random chance?

16. Sex Determination in Humans
Of the 23 pairs of chromosomes in your cells, there is one pair that may not be identical.

17. Sex Determination in Humans
If you are born female, you will have 2 X chromatids
If you are born male, you will have 1X and 1Y chromatid
What will your offspring be?

18. Sex Determination in Humans
So who is responsible for the gender of their offspring?

19. Sex Determination in Humans
Along with determining gender, the sex chromosomes also contain other genes that control certain traits
Because the size of the X and Y chromatids are so different, the X chromatid contains some genes that the Y chromatid does not.
An example is the gene that controls an individual’s ability to distinguish between red and green.

20. Colour-Blindness
If a person cannot distinguish between red and green they are said to be colour-blind
The gene that controls this trait is only found on the X chromatid.
The dominant version of the gene results in normal vision
The recessive version of the gene results in colour blindness

21. Colour-Blindness
What would the phenotype for the following genotypes be?
Gender
Genotype
Phenotype
Female
XNXN
XNXn
XnXn
Male
XNY
XnY

22. Colour-Blindness
So for a female to be colour blind, she must have inherited 2 recessive copies of the gene
For a male to be colour blind he only needs to inherit one recessive copy of the gene.
Characteristics such as colour-blindness, that are controlled by genes found on the sex chromosomes, are called sex-linked traits.

23. Sex-Linked Traits
All the sex-linked genes that have been studied so far are found on the X-chromatid.
As a result, sex-linked traits are more commonly exhibited by males than females
One copy of a recessive gene will be masked by a dominant copy in females
One copy of a recessive gene will be expressed in males