Understanding Biological Inheritance GREGOR MENDEL

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Word List DominantPunnett squareHomozygous MendelRecessivePea plants GenotypeHybridPhenotype GeneDNAAllele HeterozygousPurebredCarrier HeredityChromosomesSex-linked trait Yellow seed coatBlue eyesBrown hair

Gregor Mendel Austrian monk & mathematician “The Father of Genetics” Experimented with garden peas (Pisum sativum) Grow & reproduce quickly Matings can be controlled Show a number of distinct traits that are easy to observe Studied peas for 8 years! Designed simple experiments and observed only one trait at a time Used math to formulate his conclusions – Mendel’s Laws

Traits that Mendel studied:

Mendel’s Big Idea! Genes are found in pairs Characteristics are controlled by unit factors (genes) that exist in pairs in organisms and are passed from parents to offspring When two parents produce an offspring, each parent gives one of the factors from each pair Mendel’s garden

Mendel’s 1st Law 1. Law of Dominance: In a cross of parents that are pure for contrasting traits, only one form of the trait will appear in the next generation. Offspring that are hybrid for a trait will have only the dominant trait in the phenotype. One factor is dominant and the other is recessive

Law of Dominance (cont)

Mendel’s 2 nd Law 2. The Law of Segregation: During the formation of gametes (eggs or sperm) in meiosis, the two alleles (letters) responsible for a trait separate from each other. Alleles for a trait are then "recombined" at fertilization, producing the genotype for the traits of the offspring. When hybrids are crosses, the resulting ratio of phenotypes is 3 dominant : 1 recessive.

Mendel’s 3 rd Law 3. The Principle of Independent Assortment Alleles for different traits are distributed to sex cells (& offspring) independently of one another. This Law is easiest explained when setting up dihybrid Punnett squares in 16 boxes

Independent Assortment (cont)

Dihybrid Set Up