1. Genetics
Notes 3

2. Test Cross
How do we know if an organism that shows a dominant trait has a two dominant alleles or one dominant and one recessive allele?
A _________________ is a method for determining whether an organism that ___________________ ___________________________________________________________________________________.

3. Test Cross
In a test cross, _________________________ _____________________________________.
If the test organism is heterozygous, ___________ ________________________________________.
If the test organism is homozygous dominant, ________________________________________.
Large numbers of offspring are necessary for valid results.

4. Test Cross
Example:
In guinea pigs, black coat color is dominant over white. How would you find out whether a black guinea pig is homozygous for coat color (BB) of heterozygous (Bb)?
__________________________________________________________________________________________________________________________.

5. Test Cross
Using the Punnett Squares below, show the test cross described above:

6. Multiple Alleles
So far, we have discussed traits that have only two possible alleles (Ex. Yellow/Green; Tall/Short; Round/Wrinkled), but for many genes, several alleles exist in the population.
This is called _______________________
This expands the number of possible _____________________________

7. Multiple Alleles
Example: Multiple alleles control the character of ____________________ in humans. A person may be ______, ______, ______, or ______.
The letters refer to _______________________, called A and B, which are _____________________________ _______________________
A persons red blood cells may be coated with _____ _____________ (A or B), ___________ (AB), or _____________ (O)
The alleles are written as
IA = _____
IB = _____
i = ______

8. Multiple Alleles Each person inherits ___________________________.
There are 6 possible ways to inherit the alleles:
_______
O (i allele) is _________________
A and B (IA and IB alleles) are called ________________: ______________________________
Both carbohydrate A and B are present on red blood cells

9. Multiple Alleles How is this different from incomplete dominance?
______________________________________________________________________
Ex. ______________________________
___________________________________

10. Genotype
Phenotype ii
IAIA
IAi
IBIB
IBi
IAIB

11. Review: Dihybrid Cross
Using the Punnett square below, work out the following cross:
TTYY x TtYy

12. Review: Dihybrid Cross
Using the Punnett square, work out the following cross:
rrYy x RRyy

13. Review: Blended Inheritance (Incomplete Dominance)
Example:
Crossing pure red (RR) and pure white (WW) Japanese four-o’clock flowers results in an F1 generation in which all of the flowers are pink (RW). Show a cross between a pure red flower (RR) and a pure white flower (WW).
Phenotypes:_________

14. Review: Blended Inheritance (Incomplete Dominance)
Show a cross between two members of the F1 generation (RW x RW). Phenotypes:_________

15. Review: What is Mendel’s law of independent assortment?
What is incomplete dominance?
What is codominance?
When do you use a test cross?
When do you use a dihybrid cross?
When do you use a monohybrid cross?