1. Variation and Inheritance
National 5 Biology
Key Area 5:
Variation and Inheritance
National 4 Biology
Key Area 4
Genetic Information

2. By the end of the lesson you will be able to …..
Give reasons why the actual phenotype ratio is different from the predicted.
Use the Genetics specific vocabulary confidently

3. Actual figures vs. predicted figures in a cross
50% of gametes contain the P (purple) allele
50% of gametes contain the p (white) allele.
Predicted phenotypic ratio = 3 dominant: 1 recessive

4. This cross was repeated and 100 offspring were produced.
Predicted figures
75 purple
25 white
Actual Figures
71 purple
29 white

5. Why are the actual and Predicted figures different?
This cross was repeated and 100 offspring were produced.
Predicted figures
75 purple
25 white
Actual Figures
71 purple
29 white
Why are the actual and
Predicted figures different?

6. Actual figures vs. predicted figures in a cross
In reality, there is often a difference between the actual phenotypes shown in F2 and the predicted phenotypes shown in F2.
This is because fertilisation is a random process or the sample size could be too small.

7. Genetics Language! Phenotype Genotype Allele Dominant Recessive
Homozygous
Heterozygous
True-Breeding

8. In the following example, name a) the characteristic b)the phenotype for each flower

9. Phenotype and Genotype Example
Black
White
Black
White
What characteristic do you think we are looking at?
What is the phenotype for each guinea pig?
What is DOMINAT allele?
What is the recessive allele?
What is the genotype for each guinea pig?
Using “heterozygous” and “homozygous”, describe each guinea pig

10. The physical appearance of an organism
Word
Meaning
Phenotype
Genotype
Alleles
Dominant
Recessive
Homozygous
Heterozygous
True-breeding
The physical appearance of an organism
The genes (or alleles) that an organism possesses. Usually written as letters.
Different forms of the same gene.
An allele that always expresses itself whether it is partnered by a recessive allele or by another like itself.
Describes the variant of a gene for a particular characteristic which is masked or suppressed in the presence of the dominant variant. A recessive allele will only be expressed in the phenotype if it is paired with another recessive gene
This describes a genotype in which the two alleles for the characteristic are identical.
This describes a genotype in which the two alleles for a particular characteristic are different
Describes an organism that on being crossed with a member of
the same strain always produces more organism of exactly
the same strain