2. Mendel's Laws of Inheritance

Students taking a genetics exam were expected to answer the following question by converting data to a 'meaningful ratio' and then solving the problem. The instructor assumed that the final ratio would reflect two gene pairs, and most correct answers did. Here is the exam question: 'Flowers may be white, orange, or brown. When plants with white flowers are crossed with plants with brown flowers, all the F₁ flowers are white. For F₂ flowers, the following data were obtained:

48 white

12 orange

4 brown

Convert the F₂ data to a meaningful ratio that allows you to explain the inheritance of color. Determine the number of genes involved and the genotypes that yield each phenotype.'

We now have a dilemma. The data are consistent with two alternative mechanisms of inheritance. Propose an experiment that executes crosses involving the original parents that would distinguish between the two solutions proposed by the students. Explain how this experiment would resolve the dilemma.

Students taking a genetics exam were expected to answer the following question by converting data to a 'meaningful ratio' and then solving the problem. The instructor assumed that the final ratio would reflect two gene pairs, and most correct answers did. Here is the exam question: 'Flowers may be white, orange, or brown. When plants with white flowers are crossed with plants with brown flowers, all the F₁ flowers are white. For F₂ flowers, the following data were obtained:

48 white

12 orange

4 brown

Convert the F₂ data to a meaningful ratio that allows you to explain the inheritance of color. Determine the number of genes involved and the genotypes that yield each phenotype.'

A number of students failed to reduce the ratio for two gene pairs as described above and solved the problem using three gene pairs. When examined carefully, their solution was deemed a valid response by the instructor. Solve the problem using three gene pairs

Students taking a genetics exam were expected to answer the following question by converting data to a 'meaningful ratio' and then solving the problem. The instructor assumed that the final ratio would reflect two gene pairs, and most correct answers did. Here is the exam question:

'Flowers may be white, orange, or brown. When plants with white flowers are crossed with plants with brown flowers, all the F₁ flowers are white. For F₂ flowers, the following data were obtained:

48 white

12 orange

4 brown

Convert the F₂ data to a meaningful ratio that allows you to explain the inheritance of color. Determine the number of genes involved and the genotypes that yield each phenotype.'

Solve the problem for two gene pairs. What is the final F₂ ratio?

Humans vary in many ways from one another. Among many minor phenotypic differences are the following five independently assorting traits that (sort of) have a dominant and a recessive phenotype: (1) forearm hair (alleles F and f )—the presence of hair on the forearm is dominant to the absence of hair on the forearm; (2) earlobe form (alleles E and e)—unattached earlobes are dominant to attached earlobes; (3) widow's peak (alleles W and w)—a distinct 'V' shape to the hairline at the top of the forehead is dominant to a straight hairline; (4) hitchhiker's thumb (alleles H and h)—the ability to bend the thumb back beyond vertical is dominant and the inability to do so is recessive; and (5) freckling (alleles D and d)—the appearance of freckles is dominant to the absence of freckles. In reality, the genetics of these traits are more complicated than single gene variation, but assume for the purposes of this problem that the patterns in families match those of other single-gene variants.

If a couple with the genotypes Ff Ee Ww Hh Dd and Ff Ee Ww Hh Dd have children, what is the chance the children will inherit the following characteristics?

four dominant traits and one recessive trait

Humans vary in many ways from one another. Among many minor phenotypic differences are the following five independently assorting traits that (sort of) have a dominant and a recessive phenotype: (1) forearm hair (alleles F and f )—the presence of hair on the forearm is dominant to the absence of hair on the forearm; (2) earlobe form (alleles E and e)—unattached earlobes are dominant to attached earlobes; (3) widow's peak (alleles W and w)—a distinct 'V' shape to the hairline at the top of the forehead is dominant to a straight hairline; (4) hitchhiker's thumb (alleles H and h)—the ability to bend the thumb back beyond vertical is dominant and the inability to do so is recessive; and (5) freckling (alleles D and d)—the appearance of freckles is dominant to the absence of freckles. In reality, the genetics of these traits are more complicated than single gene variation, but assume for the purposes of this problem that the patterns in families match those of other single-gene variants.

If a couple with the genotypes Ff Ee Ww Hh Dd and Ff Ee Ww Hh Dd have children, what is the chance the children will inherit the following characteristics?

all recessive traits

Humans vary in many ways from one another. Among many minor phenotypic differences are the following five independently assorting traits that (sort of) have a dominant and a recessive phenotype: (1) forearm hair (alleles F and f )—the presence of hair on the forearm is dominant to the absence of hair on the forearm; (2) earlobe form (alleles E and e)—unattached earlobes are dominant to attached earlobes; (3) widow's peak (alleles W and w)—a distinct 'V' shape to the hairline at the top of the forehead is dominant to a straight hairline; (4) hitchhiker's thumb (alleles H and h)—the ability to bend the thumb back beyond vertical is dominant and the inability to do so is recessive; and (5) freckling (alleles D and d)—the appearance of freckles is dominant to the absence of freckles. In reality, the genetics of these traits are more complicated than single gene variation, but assume for the purposes of this problem that the patterns in families match those of other single-gene variants.

If a couple with the genotypes Ff Ee Ww Hh Dd and Ff Ee Ww Hh Dd have children, what is the chance the children will inherit the following characteristics?

the genotype Ff EE Ww hh dd

In four o'clock plants, many flower colors are observed. In a cross involving two true-breeding strains, one crimson and the other white, all of the F₁ generation were rose color. In the F₂, four new phenotypes appeared along with the P₁ and F₁ parental colors. The following ratio was obtained:

1/16 crimson

4/16 rose

2/16 orange

2/16 pale yellow

1/16 yellow

4/16 white

2/16 magenta

Propose an explanation for the inheritance of these flower colors.

Situs inversus is a congenital condition in which the major visceral organs are reversed from their normal positions. Investigations into the genetics of this abnormality revealed that individuals with at least one dominant allele (SI) of an autosomal gene are normal but, surprisingly, of individuals that are homozygous for a recessive allele (si), 1/2 are situs inversus and 1/2 are normal.

What genotypes and phenotypes are expected in progeny from a cross of two SI si individuals?

Situs inversus is a congenital condition in which the major visceral organs are reversed from their normal positions. Investigations into the genetics of this abnormality revealed that individuals with at least one dominant allele (SI) of an autosomal gene are normal but, surprisingly, of individuals that are homozygous for a recessive allele (si), 1/2 are situs inversus and 1/2 are normal.

What genotypes and phenotypes are expected in progeny from a cross of two si si individuals?

A pea plant that has the genotype RrGgwwdd is crossed to a plant that has the rrGgWwDd genotype. The R gene controls round versus wrinkled seed, the G gene controls yellow versus green seed, the W gene controls purple versus white flower, and the D gene controls tall versus short plants. Determine the following;

What proportion of the progeny are expected to have the genotype rrggwwdd?

A pea plant that has the genotype RrGgwwdd is crossed to a plant that has the rrGgWwDd genotype. The R gene controls round versus wrinkled seed, the G gene controls yellow versus green seed, the W gene controls purple versus white flower, and the D gene controls tall versus short plants. Determine the following;

What proportion of the progeny are expected to have the genotype RrGGwwDd?

A pea plant that has the genotype RrGgwwdd is crossed to a plant that has the rrGgWwDd genotype. The R gene controls round versus wrinkled seed, the G gene controls yellow versus green seed, the W gene controls purple versus white flower, and the D gene controls tall versus short plants. Determine the following;

What are the phenotypes of each plant?