1. Do now activity #2
Write down an example of homozygous dominant genotype.
Write down an example of homozygous recessive genotype.
Write down an example of heterozygous genotype.
Described the relationship shared between the genotype and the phenotype.

2. Essential Question: Section 3-2: alleles
Where do children receive their genotypes from and how does it effect their phenotypes?
Key-terms: genotype, phenotype, allele, trait, gene, heterozygous, homozygous, dominant, recessive
Learning Target
Distinguish between dominant and recessive traits.
Distinguish between heterozygous and homozygous genotypes.
Explain how the genotype of an organism results in the phenotype of the organism.
Section 3-2: alleles

3. Don’t forget to chunk your notes!

4. Alleles occur in pairs (2).
overview
Alleles occur in pairs (2).

5. We get one from ___ & one from ___ .
overview
Mom/dad
We get one from ___ & one from ___ .
Mom
Dad

6. Dominant traits are written with an __________ allele.
overview
Uppercase letter
uppercase
Dominant traits are written with an __________ allele.

7. Recessive traits are written with a ____________ allele.
overview
lowercase letter
Recessive traits are written with a ____________ allele.
lowercase

8. Don’t forget to chunk your notes!

9. ___________ alleles are the same.
Same or different
homozygous
___________ alleles are the same.
Homozygous

10. Homozygous _______ alleles are both capitalized.
Same or different
dominant
Homozygous _______ alleles are both capitalized.
dominant

11. Homozygous _______ alleles are both lowercase.
Same or different
recessive
Homozygous _______ alleles are both lowercase.
recessive

12. ___________ alleles are different.
Same or different
heterozygous
Heterozygous
___________ alleles are different.

13. Don’t forget to chunk your notes!

14. What we can physically see
now you see me…
Phenotype
What we can physically see

15. now you don’t! Genotype These are the genetic “codes” we do not see
They are the allele pairs that we received from mom & dad

16. Practice Question!
In humans, straight thumb (S) is dominant over hitch-hikers thumb ( s ). Use a Punnett square to predict the probability of having a baby with hitch-hiker thumb for two people heterozygous for straight thumb.
cyclins

17. Practice Question! And S s S s S S S s S s s s
Heterozygous for straight thumb
And
Heterozygous for straight thumb.
S s S s
S S
S s
cyclins
S s
s s

18. There is a 75% chance that the baby will have straight thumb.
Practice Question!
There is a 75% chance that the baby will have straight thumb.
S s S s
S S
S s
cyclins
S s
s s

19. There is a 25% chance that the baby will have hitch-hikers thumb.
Practice Question!
There is a 25% chance that the baby will have hitch-hikers thumb.
S s S s
S S
S s
cyclins
S s
s s

20. Don’t forget to chunk your notes!

21. Some alleles are not as simple as either dominant or recessive
Exceptions to the rule
Some alleles are not as simple as either dominant or recessive

22. Some alleles are neither dominant nor recessive
Exceptions to the rule
Some alleles are neither dominant nor recessive

23. Many traits are controlled by multiple alleles or genes
Exceptions to the rule
Many traits are controlled by multiple alleles or genes

24. 1. Incomplete Dominance is when one allele is not completely dominant over the other
Example:
RR = red flower
rr = white flower
Rr = pink flower
The exceptions

25. The exceptions
2. Codominance is when both alleles contribute to phenotype
Example:
RR = red flower
rr = white flower
Rr = red & white flower

26. The exceptions
3. Multiple Alleles is when more than two alleles contribute to the phenotype
Example:
Blood type A
Blood type B
Blood type AB
Blood type O

27. 4. Polygenic Traits is when many traits produced by the interaction of several genes
Examples:
Hair color
Eye color
Height
The exceptions

28. Practice Problem
Feathers in chickens are co-dominant. Chickens can have black or white feathers. Heterozygous genotypes will result in speckled chickens (black AND white).
__________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________
A speckled rooster ( F B F W ) mates with a hen that has white feathers ( F W F W ).
*Use a punnet square to determine the probability of the chickens having a chick with white feathers.

30. Practice Question! F B F W F W F W And A speckled rooster ( F B F W )
a hen with white feathers
( F W F W )
F B F W
F B F W
F W F W
cyclins
F W F W
F B F W
F W F W

31. There is a 50% chance that the chick will have speckled feathers.
Practice Question!
There is a 50% chance that the chick will have speckled feathers.
F B F W
F B F W
F W F W
cyclins
F W F W
F B F W
F W F W

32. There is a 50% chance that the chick will have white feathers.
Practice Question!
There is a 50% chance that the chick will have white feathers.
F B F W
F B F W
F W F W
cyclins
F W F W
F B F W
F W F W

33. There is a 0% chance that the baby will have black feathers.
Practice Question!
There is a 0% chance that the baby will have black feathers.
F B F W
F B F W
F W F W
cyclins
F W F W
F B F W
F W F W