Presentation on theme: "The Basics of Genetics…the passing of traits"— Presentation transcript:
1 The Basics of Genetics…the passing of traits Our genes determine our traits or characteristics.Your genotype (Dd) or genetic makeup for a particular trait determines your phenotype (dimples) or physical appearance for that trait.Alleles are different forms that a gene may have for a single trait. For example, having dimples or not having dimples.
2 Alleles can be represented by letters Alleles can be represented by letters. You get one allele from each parent; that’s why there are 2 letters.Alleles can be dominant, represented by a capital letter or recessive, represented by a lowercase letter.Homozygous (pure) = 2 of the same alleles for a trait; for example: dd or DDHeterozygous (hybrid) = 2 different alleles for a trait; for example: Dd
4 Punnett squaresA chart that shows the chances or probability of a particular trait being expressed in offspring.Each box of the Punnett square represents a 25% chance for that trait being expressed.Example: Cross Tt and ttT = dominant allele = tallT = recessive allele = shortThe Tt and tt along the top and sides of the Punnett square are the genotypes for the parents.The genotypes for the offspring are inside of the Punnett square.
5 Interpreting Punnett squares Remember that T is dominant over t, which is recessive.Parent 1’s genotype = tt; phenotype = shortParent 2’s genotype = Tt; phenotype = tallThere is a 50% chance of producing short offspring = tt because there are 2 boxes with that trait.There is a 50% chance of producing tall offspring = Tt.
6 Pedigree Charts (also see Pedigree notes) There are four generations shown on this pedigree chart.Squares = males and circles = females; if the shape is totally shaded then he/she has the condition; if the shape is shaded ½ way then he/she is a carrier for that condition.Generation I parents had 2 boys and 3 girls of which only 1 has the condition.