1. How to PREDICT offspring?
Punnett squares
How to PREDICT offspring?

2. Traits Your characteristics Can be PHYSICAL – how your body LOOKS
eye color & hair color
Can be PHYSIOLOGICAL – how your body WORKS
cystic fibrosis, sickle cell anemia, diabetes

3. Alleles Different forms of a gene Think of the word OPTIONS!!
Alleles for eye color
Blue, brown, green, hazel, etc.
Think of the word OPTIONS!!

4. Dominant t T The allele that SHOWS Written with a CAPITAL letter
In pea plants, tall is
DOMINANT over short
T = Tall
t = Short
t T

6. Recessive
The allele that is HIDDEN unless you get it from BOTH parents.
Written with a lowercase letter
If Yellow is dominant…what letters do we use?
If Yellow is dominant…what letters do we use?
Y – yellow y - green
Y – yellow y - green
If Round is dominant…what letters do we use?
If Inflated is dominant…what letters do we use?
R – round r - wrinkled
I – inflated i - constricted

7. Homozygous/Pure Homo means SAME When both alleles are the SAME
TT or tt

8. Heterozygous/Hybrid Hetero means DIFFERENT
When both alleles are DIFFERENT Tt

9. If these two mice have different alleles…why do they look EXACTLY ALIKE?
Because the dominant allele HIDES the recessive allele.

10. Phenotype PHenotype – PHysical features Use descriptive words ONLY!!
Tall, short, yellow, green,etc.
TT = tall
tt = short
Tt = _______
tall

11. Genotype Genetic make-up for a trait ‘Type-o-Genes’
To figure out genotype, ask 2 questions:
Homozygous or Heterozygous?
Dominant or Recessive?
TT – Homozygous Dominant
Tt – Heterozygous
tt – Homozygous Recessive

12. Genotype Determines Phenotype

13. Punnett Square A tool used to PREDICT offspring outcome
Shows the cross between two parents
If a heterozygous tall plant is crossed with a short plant (Tall is dominant), what kind of offspring would be possible?
Tt x tt
T t t
Genotype
Phenotype Tt tt
2/4 Heterozygous
2/4 Tall Tt tt
2/4 Hom Recessive
2/4 Short

14. Punnett Square TT TT Tt Tt T t T T
The letters on the OUTSIDE of the Punnett Square represent the SPERM and EGG of the parents
P generation TT TT Tt Tt
The letters on the INSIDE of the Punnett Square represent the OFFSPRING (Babies)
F1 generation

15. Practice Problem Bb Bb Bb Bb
In rabbits Brown fur is dominant to White fur. What would the offspring be when a Homozygous brown rabbit mates with a white rabbit?
B = brown b = white
BB x bb
B B
Genotype
Phenotype Bb Bb b
4/4 Heterozygous
4/4 Brown Bb Bb

16. Practice Problem
In Pea plants, tall plants are dominant over short plants. What would the offspring be if two hybrid pea plants pollinated?

17. Practice Problem
In rose bushes, straight thorns are dominant over curved thorns. If a homozygous dominant straight-thorned rose bush pollinates a homozygous dominant curved-thorned rose bush what kind of thorns would their offspring have?

18. Practice Problem
In rabbits, brown fur is dominant to white fur. If two white rabbits mate and have offspring with brown hair, what do we know about both parents? Show the Punnett square to prove your answer.

19. Practice Problem
In beagles, white snouts are recessive to brown snouts. What would the offspring look like if a white snout beagle mates with a hybrid brown snout beagle?