1. I look all white but my Dad was black The Who - ‘Substitute’
Single Trait Inheritance

2. Kenosha Robinson
Was born with albinism, a recessive genetic condition that affects one of every seventeen thousand births.
Albinism affects the genes that code for the production of the pigment melanin which gives skin its colour.

3. Terms Used in Genetics Alleles
Alleles are alternate genes that code for different variations of the same heritable characteristic.
Alleles for the same characteristic are found at the same locations on homologous chromosomes.
When the zygote is formed, sexually produced organisms receive one allele for each trait from each parent

4. Terms Used in Genetics Genotype vs. Phenotype
The observable traits of an individual.
The alleles an organism contains for a specific trait.
One allele for each trait is inherited from each parent.
We express genotypes using large and small letters.
Tall Tree
TT or Tt

5. Homozygous vs. Heterozygous
Terms Used in Genetics
Homozygous vs. Heterozygous
A genotype in which the alleles of a pair are different.
A genotype in which both alleles of a pair are the same.
tt or TT Tt

6. Punnet Squares
A Punnet square is a chart used by geneticists to show the possible combinations of alleles in offspring.
Punnet squares give us information about the genotypes and phenotypes of offspring.

7. Sample Problem One
Consider a cross between a pea plant that is heterozygous for round seeds with a pea plant that has wrinkled seeds. The allele for round seeds is dominant over that for wrinkled seeds. R can be used to represent the round dominant allele and r can be used to represent the wrinkled recessive allele. Determine the genotypes and phenotypes of the offspring. [Ritter et. al., 2002, p. 135]

8. Heterozygous (Rr) x Homozygous Recessive (rr)
Sample Problem One
Heterozygous (Rr) x Homozygous Recessive (rr) r R r Rr Rr rr rr

9. Heterozygous (Rr) x Homozygous Recessive (rr)
Sample Problem One
Heterozygous (Rr) x Homozygous Recessive (rr) r R r Rr Rr rr rr

10. Heterozygous (Rr) x Homozygous Recessive (rr)
Sample Problem One
Heterozygous (Rr) x Homozygous Recessive (rr) rr R r Rr
Genotypic Ratios
RR (0) : Rr (2) : rr (2)
50% Rr and 50% rr
Phenotypic Ratios
Round (2) : Wrinkled (2)
50% Round
50% Wrinkled

11. Sample Problem Two
Consider a cross between a plant that is homozygous for yellow seeds with a plant that is homozygous for green seeds. If the yellow condition is dominant over the green condition, what are the genotypic and phenotypic ratios in the F1 Generation?

12. Homozygous Domniant (YY) x Homozygous Recessive (yy)
Sample Problem Two
Homozygous Domniant (YY) x Homozygous Recessive (yy) Y y Yy Yy Yy Yy

13. Homozygous Domniant (YY) x Homozygous Recessive (yy)
Sample Problem Two
Homozygous Domniant (YY) x Homozygous Recessive (yy) Y y Yy Yy Yy Yy

14. Homozygous Domniant (YY) x Homozygous Recessive (yy)
Sample Problem Two
Homozygous Domniant (YY) x Homozygous Recessive (yy) y Y Yy
Genotypic Ratios
YY (0) : Yy (4) : yy (0)
100% Yy
Phenotypic Ratios
Yellow (4) : Green (0)
100% Yellow

15. Sample Problem Three
Consider a cross between offspring from the F1 Generation in the previous question. What are the genotypic and phenotypic ratios in the F2 Generation?

16. Heterozygous (Yy) x Heterozygous (Yy)
Sample Problem Three
Heterozygous (Yy) x Heterozygous (Yy) y Y Y y YY Yy Yy yy

17. Homozygous Domniant (YY) x Homozygous Recessive (yy)
Sample Problem Three
Homozygous Domniant (YY) x Homozygous Recessive (yy) y Y Y y YY Yy Yy yy

18. Homozygous Domniant (YY) x Homozygous Recessive (yy)
Sample Problem Three
Homozygous Domniant (YY) x Homozygous Recessive (yy) Y y YY yy Yy
Genotypic Ratios
YY (1) : Yy (2) : yy (1)
25% YY : 50% Yy : 25% yy
Phenotypic Ratios
Yellow (3) : Green (1)
75% Yellow
25% Green

19. A test cross can be used to determine the genotype of a dominant phenotype. Test crosses are always performed between the unknown dominant and a homozygous recessive genotype. g G ? Gg Gg ?g ?g

20. Homework Problems P. 138 Q. 3 a – e, 4 a – b
Two heterozygous tall parents are crossed. t T T t TT Tt Tt tt

21. Homework Problems P. 138 Q. 3 a – e, 4 a – b
Two heterozygous tall parents are crossed.
Genotypic Ratios
TT(1) : Tt (2) : tt (1)
25% TT : 50% Tt : 25% tt
Phenotypic Ratios
Tall (3) : Short (1)
75% Tall
25% Short T t TT tt Tt