Punnett squares and Pedigree Charts

The Basics of Geneticsthe 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. Alleles can be represented by letters. You get one allele from each parent; thats 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 DD Heterozygous (hybrid) = 2 different alleles for a trait; for example: Dd Punnett squares and Pedigree Charts Punnett squares

A 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 tt T = dominant allele = tall T = recessive allele = short The 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. Interpreting Punnett squares Remember that T is dominant over t, which is recessive. Parent 1s genotype = tt; phenotype = short Parent 2s genotype = Tt; phenotype = tall There 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. 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 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.

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