1. Dominant vs. Recessive and Genotype vs. Phenotype

2. Do you have a widow’s peak?
Can roll your tongue?
Yes: No:
Do you have a widow’s peak?
Yes: No:
Do you have unattached earlobes?
Yes: No:

3. These are all DOMINANT traits.
We tend to see these traits more often in society.
Why is that?
YOU WILL LEARN TODAY!

4. Things we already know:
Chromosomes are made up of ______________
Genes code for ____________
A pair of genes that interact to code for a trait are called ________
GENES
TRAITS
GENE PAIRS OR ALLELES

5. That’s why we have a variety of skin tones in the world!
Skin tone is an example of a trait that is controlled by multiple genes.
That’s why we have a variety of skin tones in the world!

6. So let’s focus on some traits that are only controlled by ONE gene.
These are the traits that you either have one form or the other.
There’s no in-between.
What are some examples of traits controlled by only ONE gene (from your HW!)

7. Curliness of hair: Two forms?
Hairline: Two forms?
Widow’s peak vs. straight
Handedness: Two forms?
Right handed vs. left handed
Earlobes: Two forms? `
Attached vs. unattached
Curliness of hair: Two forms?
Curly vs. straight
Freckles: Two forms?
Freckles vs. no freckles
Dimples: Two Forms?
Dimples vs. no dimples
Cleft Chin: Two Forms?
Cleft chin vs. no cleft chin

8. How do we inherit either form of one of these traits?
KP#1: There are two types of genes: dominant (CAPITAL LETTER) and recessive (lowercase letter).
This guy represents a dominant gene. Dominant means strong
This guy represents a recessive gene. recessive means weak

9. Is it a Dominant or a Recessive Gene?
LETS PRACTICE!
Is it a Dominant or a Recessive Gene? b f
RECESSIVE
RECESSIVE g T
DOMINANT
RECESSIVE r L
RECESSIVE
DOMINANT

10. Our two genes combine to make a trait:
AA = two dominant genes = shows dominant trait
aa = two recessive genes = shows recessive trait
Aa = one dominant and one recessive gene
What do you think will show?
DOMINANT! DOMINANT BEATS RECESSIVE
Which guy do you think represents the dominant gene and which guy represents the recessive gene?

11. WHAT’S THE RULE??
KP #2: A dominant trait will show if you have ONE or TWO dominant genes.
 AA or Aa
KP #3: A recessive trait will show ONLY if you have TWO recessive genes.
 aa

12. Will these gene combinations show a Dominant or a Recessive Trait?
LETS PRACTICE!
Will these gene combinations show a Dominant or a Recessive Trait? bb Ff
RECESSIVE
DOMINANT TT Gg
DOMINANT
DOMINANT rr LL
RECESSIVE
DOMINANT

13. Another word for gene combinations is GENOTYPE. (THINK GENE)
Who’s tired of saying GENE COMBINATION?
KP# 4:
Another word for gene combinations is GENOTYPE. (THINK GENE)
EX: Aa = genotype
Another word for trait or the way an organism looks or behaves is PHENOTYPE. (THINK PHYSICAL)
Ex: Curly hair = phenotype

14. LETS PRACTICE! Jj: Cc: Tt: Freckles: Straight hair line: Dimples:
Genotype or Phenotype?
Jj:
Straight hair line:
Genotype
Phenotype
Cc:
Freckles:
Genotype
Phenotype
Tt:
Genotype
Dimples:
Phenotype

15. What about wavy hair? What gene combination do you think creates wavy hair?
-Aa
KP #5: Sometimes the dominant gene does not completely overpower the recessive gene. This is called incomplete dominance.

16. CANDY QUESTION: Could it be possible for this little girl to have her own daughter some day with straight hair?

17. YES! HOW?
If the curly haired girl has a genotype that shows INCOMPLETE DOMINANCE, she still has an allele for straight hair. She could pass that on to her own child.
What genotype MUST this little girl have?
aa = straight hair
aa = straight hair or
Aa = wavy hair
What genotype must this girl’s MOTHER have?

18. YOUR TURN TO SHOW WHAT YOU LEARNED!
START YOUR INDEPENDENT PRACTICE NOW.