Genes and alleles

1. Genes and alleles 3.14 Understand that a gene is a section of a molecule of DNA • A gene is a short section of DNA along the length of the chromosome. • Each gene codes for a specific protein, which in turn will determine a specific characteristic or function.

2. 3.16 Understand that genes exist in alternative forms called alleles which give rise to differences in inherited characteristics Genes and Alleles • A gene codes for a specific protein (which in turn determines a characteristic). • Alleles are different forms of the same gene. Example: • The gene which codes for eye colour may have the alleles blue, green, brown, hazel or black.

3. For each gene there will be two allelespresent, so for eye colour you may have a blue allele and a brown allele. So which colour of eyes do you end up with? • This all depends whether the alleleis dominantor recessive. • Dominant alleles are represented by capital letters e.g. the allele for Brown eyes (B). • Recessive allelesare represented by lower case letters e.g. the allele for blue eyes is (b).

4. If you have a dominant allele – it is ALWAYS EXPRESSED

5. Definitions

6. Definitions

7. 3.18 Describe patterns of outcomes from monohybrid inheritance • Blue eyes (b) is recessive to brown eyes (B). • What are the chances of parents having blue eyed children if the father is heterozygous for brown eyes (Bb) and the mother has blue eyes (bb)? • Parents Phenotypes BrownxBlue • Parents Genotypes Bb xbb • Gametes Bb x bb

8. Parents Phenotypes Brown x Blue • Parents Genotypes Bb x bb • Gametes Bb x bb Genetic Cross (Punnett Square) • Offsrping Genotype 50% Bb : 50% bb • Offspring Phenotype 50% Brown : 50% Blue