3.5.3. Codominance and intermediate inheritance (problems solved)

Codominance and intermediate inheritance (problems solved). (Page 14)

You will remember from when we saw the types of genetic inheritance, that intermediate dominance occurs when the phenotype of the heterozygous, descended from two different codominant homozygous parents, presented an intermediate phenotype between that of the two parents.

In codominance, on the other hand, the heterozygous offspring manifests a phenotype in which the characteristics of both parents are manifested.

In addition to the problems you have below, you have more problems of this type on the next page:

More codominance and intermediate inheritance problems (15).

Nomenclature for genetic problems

Since uppercase letters represent dominance and lowercase letters, recessivity, in the case of codominance problems, we will represent the different alleles by means of subscripts or superscripts of the same representative letter of the gene. We will capitalize this letter, since both alleles are expressed to a greater or lesser degree. For example, A₁ A₂.

In the case of blood groups the MN system, the gene is represented by the letter L and the two alleles are L^M and L^N. Possible genotypes are L^ML^M, L^NL^N and L^ML^N.

Genetics problem 103

In one species of plants the flowers can be red, white or pink. It is known that this trait is determined by two allele genes, red (C^r) and white (C^b) , with intermediate inheritance.

How could they be the descendants of the cross between plants with pink flowers?

Genetics problem 104

In one species of plants the flowers can be red, white or pink. It is known that this trait is determined by two allele genes, red (C^r) and white (C^b), with intermediate inheritance.

How could they be the descendants of the cross between plants with pink flowers and plants with red flowers?

Genetics problem 105

In one species of plants the flowers can be red, white or pink. It is known that this trait is determined by two allele genes, red (C^r) and white (C^b) , with intermediate inheritance .

How could they be the descendants of the cross between plants with pink flowers and plants with white red flowers?

Nomenclature for genetic problems

In cases of intermediate inheritance, a new phenotype appears, although it does not necessarily have to be intermediate. They are different alleles of the same gene, so we will use a single letter for all of them.

We can use an uppercase letter (A) and a lowercase letter (a), since in this case there is neither dominance nor recessivity, or use a capital letter for the two alleles, with a subscript or superscript to differentiate them (C¹, C²).

Genetics problem 106

In a certain breed of hen, the C^N allele indicates black, the C^B , white, both codominant, and when both alleles appear in an individual, C^NC^B , the hen's plumage is blue.

a) How are the descendants of the crossing of a blue hen and a black hen?

b) How are the descendants of the cross between two blue chickens?

c) How are the descendants of the crossing of a blue hen and a white hen?

Genetics problem 107

Reason the answers: The PP genotype determines the presence of ruffled feathers in hens, while pp produces smooth feathers and Pp, gives rise to an intermediate phenotype. Of the crossing of a hen with curly feathers and a rooster with smooth feathers,

a) what proportion of their offspring is expected from intermediate feathers?

b) and what proportion of intermediate feathers will be obtained from crossing a rooster and hen with intermediate feathers?

c) why can't Mendel's laws apply to prokaryotic organisms?

Genetics problem 108

By crossing a gray-winged butterfly with another with black wings, an offspring made up of 93 black-winged butterflies and 93 gray-winged butterflies was obtained. The gray-winged butterfly was crossed with another with white wings, obtaining an offspring made up of 35 white butterflies and 35 gray butterflies. Find out the genotypes, both of the butterflies that are crossed and of the offspring. Reason for the answer.

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a) The gray butterfly (C^BC^N) was crossed with the black one (C^NC^N) and 93 gray and 93 black were obtained.

Crossing: C^NC^N x C^BC^N

Gametes: C^N C^B C^N

F1: C^BC^N C^NC^N 93 gray and 93 black, 1: 1 ratio

b) The gray-winged butterfly (C^BC^N) was crossed with another with white wings C^BC^B, obtaining an offspring made up of 35 white butterflies (C^BC^B ) and 35 gray butterflies (C^BC^N) .

Crossing: C^BC^B x C^BC^N

Gametes: C^B C^B C^N

F1: C^BC^N C^BC^B 35 gray and 35 white, 1:1 ratio

Genetics problem 109

Two "morning glory" plants are homozygous for flower color. One of them produces ivory flowers and the other red flowers. Tell how the genotypes and phenotypes originating from the crossing of both plants will be, knowing that "B" is the gene responsible for the ivory color and "R" is the one that conditions the red color, both genes being equipotent.

Genetics problem 110

A gardener who had rose-flowered morning glory plants crossed two of his plants with the idea of obtaining plants of the same color. His surprise was that red, pink and white flowers appeared in the offspring in the ratio 1: 2: 1.

Indicates the genotype of the plants of the described cross.

Genetics problem 111

In guinea pigs there are three varieties for the coat: yellow, cream and white. Crossing two cream-colored guinea pigs produces descendants of all three varieties. Deduce what type of inheritance the character presents by raising the cross.

Geneticx problem 112

There are varieties of a plant with white flowers and varieties with purple flowers. The F1 of a cross between plants of the two varieties was light purple, and the F2 gave 1/4 violet, 2/4 light violet and 1/4 white. Explain the type of inheritance and perform the crossing.

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