Predicting the Inheritance of Alleles Learning Goal: To predict the results of a cross between two individuals for a characteristic. Success Criteria: use a Punnett squares to predict the results of a cross between two individuals for a trait determine possible phenotypes and genotypes of offspring produced from a cross determine phenotype and genotype ratios of offspring produced from a cross predict an unknown genotype using test crosses Why do we resemble our parents? (We resemble our parents because we inherit traits from them.) 2. Why does asexual reproduction result in genetic clones? (During asexual reproduction, the organism makes a copy of itself without combining its genes with those from another organism. The offspring are a genetic copy of the single parent.) 3. Why are the offspring of sexual reproduction not genetically identical to either parent? (During sexual reproduction, genes from two individuals combine to produce offspring with new combinations of genes.)

Predicting the Inheritance of Alleles geneticists use monohybrid crosses to study inheritance involves the inheritance of two alleles for a single characteristic punnett square: a diagram used to predict the proportions of genotypes in the offspring resulting from a cross between two individuals Mendel’s experiments consisted of many crosses. As a result of these experiments, he developed a way of mathematically predicting the proportions of phenotypes in the off spring.

Predicting the Inheritance of Alleles Cont’d… probability is a measure of the chance that an event will happen punnett squares are used to predict the probability of different genotypes and phenotypes that may result from a given cross they are also a graphic summary of every possible combination of maternal and paternal alleles In the following tutorial, you will learn how to set up Punnett squares, execute crosses, and interpret the results.

Predicting Single-Characteristic Inheritance Cont’d… Example #1: In pea plants, the allele for yellow seed colour, Y, is dominant over that for green seed colour, y. A pea plant that is homozygous for yellow seeds is crossed with a plant that is homozygous for green seeds. Determine the possible genotypes and phenotypes of the offspring. Genotypes: Phenotypes: Step 1: Write the symbols for the gametes across the top and along the left side of the square (Figure 8). Note that each parent can supply two possible gametes, each containing one of two possible alleles. Fill in the boxes of the Punnett square by combining the gametes corresponding to each row and column. Each box represents a possible offspring genotype.

Predicting Single-Characteristic Inheritance Cont’d… Example #2: Two heterozygous yellow seed plants (Yy) are crossed. Determine the genotype and phenotype ratios of the F2 generation offspring. Genotype Ratio: 1 homozygous dominate(YY) to 2 heterozyous (Yy) to 1 homozygous recessive (yy) Phenotype Ratio: 3 yellow seed plants to 1 green seed plant In the following tutorial, you will learn how to set up Punnett squares, execute crosses, and interpret the results.

Predicting Single-Characteristic Inheritance Cont’d… Example #3: In one cross of tomato plants, 1821 red tomato plants and 615 yellow tomato plants were produced. Determine the probable genotype of the parents. Which allele is dominant? Assume that the trait is influenced by only two alleles and follows the laws of Mendelian inheritance. Use the letters R and r to represent the alleles. In the following tutorial, you will learn how to set up Punnett squares, execute crosses, and interpret the results. Phenotype Ratio:

Practice Questions Question #1: A researcher crossed a homozygous yellow seed plant (YY ) and a heterozygous yellow seed plant (Yy). Determine the genotype and phenotype ratios of the offspring. Genotype Ratio: Phenotype Ratio: In the following tutorial, you will learn how to set up Punnett squares, execute crosses, and interpret the results.

Practice Questions Cont’d… Question #2: A researcher crossed a heterozygous yellow seed plant (Yy) and a recessive green seed plant (yy). Determine the genotype and phenotype ratios of the offspring. Genotype Ratio: Phenotype Ratio: In the following tutorial, you will learn how to set up Punnett squares, execute crosses, and interpret the results.

Homework Complete worksheet “Simple Genetics”