Introduction to Genetics Introduction to Genetics 22

Mendelian GeneticsMendelian Genetics

Independent AssortmentIndependent Assortment

After Mendel’s 1After Mendel’s 1stst experiment, he still had experiment, he still had a question: “Does the segregation of one a question: “Does the segregation of one pair of alleles affect the segregation of pair of alleles affect the segregation of another pair of alleles?”another pair of alleles?”

Example: Does the gene that determines Example: Does the gene that determines whether a seed is round or wrinkled in whether a seed is round or wrinkled in shape have anything to do with the gene shape have anything to do with the gene for seed color?for seed color?

Independent AssortmentIndependent Assortment

To answer this, Mendel did a 2-factor To answer this, Mendel did a 2-factor cross.cross. P P Round Yellow Peas (RRYY) X wrinkled Round Yellow Peas (RRYY) X wrinkled

green peas (rryy)green peas (rryy) all produced round yellow peas (RrYy)all produced round yellow peas (RrYy) F1 crossed the RrYy and RrYyF1 crossed the RrYy and RrYy F2 produced 556 seeds: 315 round yellow, 32 F2 produced 556 seeds: 315 round yellow, 32

wrinkled green and 209 had combinations of wrinkled green and 209 had combinations of phenotypesphenotypes

Independent AssortmentIndependent Assortment

From this, Mendel created the From this, Mendel created the Principle Principle of Independent Assortmentof Independent Assortment: states that : states that genes for different traits can segregate genes for different traits can segregate independently during the formation of independently during the formation of gametes. Independent assortment helps gametes. Independent assortment helps account for the many genetic variations account for the many genetic variations observed in plants, animals, and other observed in plants, animals, and other organisms. organisms.

Summary of Mendel’s PrinciplesSummary of Mendel’s Principles

The inheritance of biological characteristics is The inheritance of biological characteristics is determined by individual units known as genes. Genes determined by individual units known as genes. Genes are passed from parents to their offspring.are passed from parents to their offspring.

In cases in which 2 or more forms of the gene for a In cases in which 2 or more forms of the gene for a single trait exist, some forms of the gene may be single trait exist, some forms of the gene may be dominant and others may be recessive.dominant and others may be recessive.

In most sexually reproducing organisms, each adult has In most sexually reproducing organisms, each adult has 2 copies of each gene- one from each parent. These 2 copies of each gene- one from each parent. These genes are segregated from each other when gametes genes are segregated from each other when gametes are formed.are formed.

The alleles for different genes usually segregate The alleles for different genes usually segregate independently of one another.independently of one another.

PracticePractice

Create a dihybrid cross for pod shape Create a dihybrid cross for pod shape and pod color. Find the genotypic ratio and and pod color. Find the genotypic ratio and phenotypic ratiophenotypic ratio SsGg X ssggSsGg X ssgg