Genetic Problem Solving

1. Genetic Problem Solving I

2. Genetic Problem Solving • Each gamete has one gene for each trait. • After fertilization the new organism has two genes for each trait (Genotype).

3. Sperm, Egg or Zygote?

4. What the ? Gene Eye Colour Gene Homozygous Heterozygous Hair Colour Gene

5. Dominant vs. Recessive • Only one allele is expressed in the phenotype. • The allele which will always be expressed is called the Dominant allele. • The allele which may be hidden is called the Recessive allele.

6. Punnet Squares • Punnet Squares are usedto determine the probability of an offspring having a particular genotype. • We can also work out what the expected phenotype will be. • It is made by comparing all the possible combinations of alleles from the mother with those from the father.

7. Punnet Square Practice • If two parents are both heterozygous for the tongue rolling gene, predict what genotype and phenotype their offspring may have. • Roller allele is dominant (R) • Non-roller allele is recessive (r)

8. Punnet Square Practice Female r R R Rr RR Male r Rr r r

9. Genotype Phenotype • Offspring have a 25% change of being RR • 50% chance of being Rr • 25% chance of being rr • Offspring have a 75% chance of being able to roll their tongues • And a 25% chance they can not

10. Genotype vs. Phenotype • Genotype:The specific alleles an organism possesses for a trait (eg. BB, Bb or bb). • Phenotype: The physical trait an organism shows due to their genotype (Brown eyes or Blue eyes).

11. Genetic Problem Solving • If the two alleles in the genotype are the same, then the organism is said to have a homozygous genotype and is pure breeding. • If the alleles are different then the organism is heterozygous.

12. Try This • Ms. Honeypot crossed a heterozygous pea plant and a purebred plant with green peas in an attempt to create yellow peas. In pea plants, yellow peas are dominant over green peas.Use a Punnett square to predict the phenotypic and genotypic outcome (offspring).

13. Punnet Square Practice Purebred y y Y Yy Yy Heterozygus y yy yy

14. Try This • In pea plants, round peas are dominant over wrinkled peas. Use a Punnett square to predict the phenotypic and genotypic outcome of a cross between a plant homozygous for round peas and a plant homozygous for wrinkled peas.

15. Punnet Square Practice Wrinkled r r R Rr Rr Round R Rr Rr

16. Punnet Square Practice • Complete worksheet “More Punnet Practice”

17. Oink Oink! (Try This!) • Farmer Ted has a curly tailed male pig and wants to know whether it is pure breeding or not. He has asked you (the genetics expert) to find out for him? • Curly tails (T) are dominant over straight tails (t).

18. Oink (Answer) • Mate the pig in question with a female pig with a straight tail. Female Female t t t t T T Tt Tt Tt Tt Male Male T t Tt Tt tt tt

19. Conclusions • If the male was pure breeding then 100% of F1 offspring would have curly tails. • If there were ANY F1 offspring with straight tails then the male pig would not be pure breeding.

20. Test Cross • In genetics a test cross is used to determine if an individual exhibiting a dominant trait is homozygous or heterozygous. • Test crosses determine the genotype of an individual.

21. Test Cross • Test crosses involve breeding the individual in question with another individual that expresses a recessive version of the same trait. • If all offspring display the dominant phenotype, the individual in question is homozygous dominant. • If any of the offspring displays a recessive phenotype, then the individual is heterozygous.