Punnett Squares Punnett squares are used to make predictions about various inheiritance problems. The Punnett square show what might occur and not the actual results https://www.youtube.com/watch?v=d4izVAkhMPQ Work through page 136 on the board using the example, video 5.02 mins

Terminology – pg 124 Trait: A genetically determined characteristic such as hair colour, eye colour, sex etc. Dominant: An allele that is always expressed, even if only on is present.  Represented with an upper-case letter (eg C). Recessive: An allele that is only expressed when two of them are present.  Represented with a lower-case letter (eg a) Allele: Different forms of the same gene, they can be dominant or recessive. 5 mins

Alleles Different forms of a gene are called alleles. You inheirit one allele from each parent. One allele is always dominant over another eg hair colour, brown is dominant over blond The dominant allele is always written with a capital letter eg B = brown hair The recessive allele is always written with a lower case letter eg b = blond hair

Example – hair colour The dominant allele is always written with a capital letter eg B = brown hair The recessive allele is always written with a lower case letter eg b = blond hair So to have blond hair a person must have two recessive alleles or bb bb b B This information is on page 137 Bb

Example – hair colour The dominant allele is always written with a capital letter eg B = brown hair The recessive allele is always written with a lower case letter eg b = blond hair So to have blond hair a person must have two recessive alleles or bb bb b B Bb bb Bb

Complete the questions Example – hair colour If we use the same example we can find the probability of the offspring of these two having blond or brown hair. To have brown hair the allele combination can be BB or Bb so the probability of having brown hair is 2 our of 4 written as ½ or 50%. To have blond hair the allele combination has to be bb as it is recessive so the probability of having blond hair is 2 out of 4 written as ½ or 50%. bb Complete the questions page 137 SciPad b B Bb bb Bb

Pure Breeding Organisms with the same alleles eg BB or bb are said to be purebred or homozygous. Organisms with different alleles are heterozygous. Add these 2 words to the top of page 138 your definitions

Phenotype and Genotype Phenotype = the visible physical characteristic of an organism eg brown hair Genotype = internally coded genetic information eg Bb or BB for brown hair Add these 2 definitions to gap on page 138 or 139 of your SciPad.

Activity Work through the questions on page 138 and the floppy eared rabbits page 139.

Next Class What would happen if this class reproduced? How do you get the gene to be a wizard? How do dragon characteristics get passed on?