1.3 – Characteristics and Inheritance Page 28

Keywords Alleles Genotype Phenotype Heterozygous Punnet Square Dominant Recessive Homozygeous

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

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

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

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.

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

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

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?

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

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

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%

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