predicting and calculating phenotype & genotype ratios/probabilities
Calculating phenotype ratios
- 1. Make a Punnet, for one trait, by drawing a two-by-two block of squares.
2. Label the possible alleles from one parent across the top of the squares. The possible alleles from the other parent are labeled across the left side of the block. There should be only one allele per column or row.
3. Fill in the Punnet square by crossing one column and row and writing the result in each square. So a cross of "A" and "a" should be written as "Aa." - 4. Write the amount of homozygous dominant (AA) and heterozygous (Aa) squares as one phenotypic group. Count the amount of homozygous recessive (aa) squares as another group.
5a. Write the result as a ratio of the two groups. A count of 3 from one group and 1 from the other would give a ratio of 3:1. - Punnet Square Ratio
5b. Make a Punnet, for one trait, by drawing a two-by-two block of squares.
6. Label the possible alleles from one parent across the top of the squares. The possible alleles from the other parent are labeled across the left side of the block. There should be only one allele per column or row.
7. Fill in the Punnet square by crossing one column and row and writing the result in each square. So a cross of "A" and "a" should be written as "Aa."
8. Write the amount of homozygous dominant (AA) and heterozygous (Aa) squares as one phenotypic group. Count the amount of homozygous recessive (aa) squares as another group.
9. Write the result as a ratio of the two groups. A count of 3 from one group and 1 from the other would give a ratio of 3:1.
Incomplete Dominance
10. Complete the first three steps from "Punnet Square Ratio" from above.
11. Count the number of homozygous squares in their own group. For example, each of "aa" and "bb" would be in their own respective group.
12. Count the number of heterozygous squares as a separate group.
13. Write the phenotypic ratio as a relationship of the physical traits in each group. Three distinct traits are common with incomplete
dominance. - http://www.ehow.com/how_8182896_calculate-phenotypic-ratio.html
Calculating Phenotype Probabilities
- 1.Follow steps one through three from Section 1 above.
- 2.Consult your list of dominance patterns in order to determine the phenotype for each of the four possible combinations of alleles for each gene.
- 3.Count all of the squares which contain the genotype(s) that produce the phenotype you are seeking.
- 4.Divide the number of squares from Step 3 by the total number of squares in the grid. This quotient is equal to the phenotype probability.
http://www.ehow.com/how_8288509_calculate-probabilities-likelihood-offspring.html- Calculating Genotype Ratios
- 1. Identify the alleles available for the trait. For example, a trait may have a total of eight alleles, 1, 2, 3, 4, 5, 6, 7 and 8, or as few as two alleles, such as L and l.
2. Write all the combinations of the alleles. If the alleles are 1 through 8, then start with the combination 11 and work your way to 18. Then begin the sets that have 2 in them, but leave out 12 because in genotyping no difference exists between
12 and 21. Repeat the technique for combining alleles until you make all of the combinations. As you progress through the different allele groups, the number of available combinations for each allele will decrease.
3. Count the total number of allele combinations, or genotypes, that you formed from the available alleles. If the available alleles for a trait are 1 through 8, then the total number of genotypes is 36 for that trait. - http://www.ehow.com/how_10005181_calculate-number-genotypes.html
Calculating Genotype Probabilities
- 1.Set up a grid with one parent in the rows and the other parent in the columns. The number of rows and columns should be equal to 2^n, where n is the number of genes being considered. So, use a 2-by-2 grid for a monohybrid cross, and a 4-by-4 grid for a dihybrid cross.
- 2.List all possible gamete genotypes for each parent, placing each unique gamete directly outside of a new row or column.
- 3. Fill in all of the squares by adding together the gamete genotypes from the row and column labels that belong to that square.
4. Divide the number of squares that contain the genotype you are seeking by the total number of squares. This quotient is equal to the probability of that genotype.
http://www.ehow.com/how_8288509_calculate-probabilities-likelihood-offspring.html
2. Label the possible alleles from one parent across the top of the squares. The possible alleles from the other parent are labeled across the left side of the block. There should be only one allele per column or row.
3. Fill in the Punnet square by crossing one column and row and writing the result in each square. So a cross of "A" and "a" should be written as "Aa."
5a. Write the result as a ratio of the two groups. A count of 3 from one group and 1 from the other would give a ratio of 3:1.
5b. Make a Punnet, for one trait, by drawing a two-by-two block of squares.
6. Label the possible alleles from one parent across the top of the squares. The possible alleles from the other parent are labeled across the left side of the block. There should be only one allele per column or row.
7. Fill in the Punnet square by crossing one column and row and writing the result in each square. So a cross of "A" and "a" should be written as "Aa."
8. Write the amount of homozygous dominant (AA) and heterozygous (Aa) squares as one phenotypic group. Count the amount of homozygous recessive (aa) squares as another group.
9. Write the result as a ratio of the two groups. A count of 3 from one group and 1 from the other would give a ratio of 3:1.
Incomplete Dominance
10. Complete the first three steps from "Punnet Square Ratio" from above.
11. Count the number of homozygous squares in their own group. For example, each of "aa" and "bb" would be in their own respective group.
12. Count the number of heterozygous squares as a separate group.
13. Write the phenotypic ratio as a relationship of the physical traits in each group. Three distinct traits are common with incomplete
dominance.
Calculating Phenotype Probabilities
- 1.Follow steps one through three from Section 1 above.
- 2.Consult your list of dominance patterns in order to determine the phenotype for each of the four possible combinations of alleles for each gene.
- 3.Count all of the squares which contain the genotype(s) that produce the phenotype you are seeking.
- 4.Divide the number of squares from Step 3 by the total number of squares in the grid. This quotient is equal to the phenotype probability.
2. Write all the combinations of the alleles. If the alleles are 1 through 8, then start with the combination 11 and work your way to 18. Then begin the sets that have 2 in them, but leave out 12 because in genotyping no difference exists between
12 and 21. Repeat the technique for combining alleles until you make all of the combinations. As you progress through the different allele groups, the number of available combinations for each allele will decrease.
3. Count the total number of allele combinations, or genotypes, that you formed from the available alleles. If the available alleles for a trait are 1 through 8, then the total number of genotypes is 36 for that trait.
Calculating Genotype Probabilities
- 1.Set up a grid with one parent in the rows and the other parent in the columns. The number of rows and columns should be equal to 2^n, where n is the number of genes being considered. So, use a 2-by-2 grid for a monohybrid cross, and a 4-by-4 grid for a dihybrid cross.
- 2.List all possible gamete genotypes for each parent, placing each unique gamete directly outside of a new row or column.
- 3. Fill in all of the squares by adding together the gamete genotypes from the row and column labels that belong to that square.
4. Divide the number of squares that contain the genotype you are seeking by the total number of squares. This quotient is equal to the probability of that genotype.
http://www.ehow.com/how_8288509_calculate-probabilities-likelihood-offspring.html