1. 1.3 – Characteristics and Inheritance Page 28

2. Keywords Alleles Genotype Phenotype Heterozygous Punnet Square
Dominant
Recessive
Homozygeous

4. Alleles
They are genes at the same locus or location on a chromosome. They represent the different variations of the gene
For example: the gene for flower color has two alleles:
P = purple flowers
p = white flowers

5. Dominant and Recessive Alleles
A dominant allele (denoted as a upper case letter) produces a dominant phenotype in individuals who have one copy of the allele, which can come from just one parent.
Two recessive alleles (denoted as a lower case letter) need to be present to produce a recessive phenotype. The individual must have two copies, one from each parent.
The characteristic that can be observed in the organism
The characteristic that can be hidden

6. Homozygous and Heterozygous
Two alleles that are identical An individual can be Homozygous Dominant or Homozygous Recessive
Two alleles that are different A heterozygous genotype always shows the dominant trait

7. Putting it all together
An individual with one dominant and one recessive allele for a gene will have the dominant phenotype. They are generally considered “carriers” of the recessive allele: the recessive allele is there, but the recessive phenotype is not.

8. Genotype and Phenotype
Phenotype: The observable characteristics of the individual (eg: hair colour) 
Genotype: The actual genetic information carried by the individual (alleles)
Genotype
Phenotype

9. Punnet Squares
Show the possible types of offspring produced from the mother and father’s genotype

10. Question
If both parents have the genotype Hh, (H is dominant for long hair while h is recessive for no hair) what will be the appearance of their offspring?

11. Step One
Be sure to use capital letters for the dominate genes and lower case letters for the recessive alleles
Place the mother’s alleles on the top of the Punnett square with one letter above each box. Place the father’s alleles on the left hand side of the square

12. Step Two
Fill in the squares by placing one allele from the mother and one from the father in each box. This will provide you with all possible combinations of alleles for the offspring

13. Step Three
Analyse the Punnet Square and determine the percentage of each genotype for the offspring
Each square represents a 25% chance of the offspring having that combination. If there are squares with the same combinations in them, the squares can be added together to determine the percentage.
25%
50%
25%

14. Therefore 75% of the offspring will have hair and 25% will not
Step Four
Analyse the Punnet Square and determine the percentage of each phenotype for the offspring
Remember when the dominant allele (capital letter) is present, the dominant phenotype will be displayed
25%
50%
25%
Therefore 75% of the offspring will have hair and 25% will not