Understanding Genetics: Traits, Probability, and Punnett Squares, Study notes of Genetics

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Traits & Probability

Using Punnett Squares

What Mendel Knew

● Traits are passed from parent to offspring through genes ● There are two forms to a gene, called alleles ● Each parent gives one allele to offspring ● One allele is dominant, the other is recessive

Some Genetics Vocabulary

● Homozygous- an organism has two identical alleles ○ BB or bb ○ purebred, true-breeding ● Heterozygous- an organism has two different alleles ○ Bb ○ hybrid

Some Genetics Vocabulary

● Genotype- genetic makeup of an organism ● Phenotype- physical characteristics determined by genotype

Punnett Squares & Mendel’s Experiment

● Parental generation, FF (purple flowers) x ff (white flowers)

F F

f

f Ff Ff

Ff Ff

● genotypic ratio: 100% Ff ● phenotypic ratio: 100% purple flowers

Punnett Squares & Mendel’s Experiment

● F1 generation, Ff (purple flowers) x Ff (purple flowers)

F f

F

f Ff ff

FF Ff

● genotypic ratio: 1 FF : 2 Ff : 1 ff ● phenotypic ratio: 3 purple flowers : 1 white flower

Test Cross

● Cross between an organism with an unknown genotype and an organism with a recessive genotype ○ if all offspring has the dominant phenotype, the unknown is homozygous dominant ○ if half of the offspring has a dominant and recessive phenotypic ratio of 1:1, the unknown is heterozygous