1. 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.)

2. 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.

3. 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.

4. 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.

5. 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.

6. 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:

7. 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.

8. 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.

9. Homework
Complete worksheet “Simple Genetics”