CROSSES

Monohybrid Crosses one pair of traits are considered in a cross use a special chart called a Punnett square to predict the genotype of the offspring phenotype ratio - appearance genotype ratio - genes in square

How to Work a Genetics Problem Follow these steps!

Read the problem. What information is provided in the problem? What is the trait? Cross a pure white flowered pea plant with a pure purple flowered plant. What is dominant? What letter will we use to represent this trait? Flower Color P What is recessive? Dominant – purple - What letter will we use to represent this trait? Recessive – white - p

Determine the genotypes of the parents. Cross a pure white flowered pea plant with a pure purple flowered plant. Pure purple Pure white P – purple p - white X pp PP X Pure = homozygous

3. The Principle of Segregation gene pairs separate into different gametes during meiosis each gamete has only one gene from the pair ex: Tt separates into T and t T t Meiosis T t Gametes

Law of Segregation: Determine the gametes Cross a pure white flowered pea plant with a pure purple flowered plant. P – purple p - white Pure white X Pure purple PP pp X Meiosis Meiosis P P p p Gametes Gametes

Punnett Square: place the gametes across the top and down one side Cross a pure white flowered pea plant with a pure purple flowered plant. p p P – purple p - white pp X PP P p p P P P

Punnett Square: join the gametes Cross a pure white flowered pea plant with a pure purple flowered plant. p p P p P p P – purple p - white pp X PP P p p P P P P p p P

Determine the genotype and phenotype of the offspring. Cross a pure white flowered pea plant with a pure purple flowered plant. p p P – purple p - white pp X PP P p P p P Genotype - Pp purple purple purple P P Phenotype - p p P purple purple

What is the genotype ratio? The phenotype ratio? Cross a pure white flowered pea plant with a pure purple flowered plant. p p P – purple p - white pp X PP P p P p P Genotype Pp to PP or pp 4 : 0 P P Phenotype p p P Purple to White 4 : 0

What percentage of the offspring are homozygous? Heterozygous? Cross a pure white flowered pea plant with a pure purple flowered plant. p p P – purple p - white pp X PP P p P p P Genotype Homozygous - 0% Heterozygous - 100% P P p p P

What percentage of the offspring are purple? White? Cross a pure white flowered pea plant with a pure purple flowered plant. p p P – purple p - white pp X PP P p P p P Phenotype Purple - 100% White - 0% P P p p P

Cross 2 heterozygous purple flowered pea plants.

4. The Principle of Independent Assortment Parents Genotype applies to gene pairs on different chromosomes separation (segregation) of a gene pair is not affected by gene pairs on other chromosomes separate independently Yy Tt Possible Gametes yt YT yT Yt