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3.5. Genetics problems

Genetics problems solved

We have seen Mendel's laws , their current interpretation, and you already have some knowledge of genetics that will help you to solve genetic problems.

We will start by looking at how genetic problems are solved, but then you will have to solve the problems that arise.
After the initial examples, the problems have been grouped into various categories for ease of study. These problems can be used for both 4th year ESO and 2nd year Biology Baccalaureate students. You have a lot  of solved genetics problems to practice. You should read the problem and fix it on paper. Then you can check the answer that appears interactively when you click on "Problem solved ". As always, if you have any questions, you can use the forums so that other users can give you a hand.

How to solve genetic problems

  • First we must read the problem carefully and analyze all the data they give us. We will write down the genotypes and phenotypes of parents and descendants that we know .
  • We have to indicate how we have named the alleles, recognizing which is the dominant allele and which is the recessive. We will represent the dominant character with a capital letter, and the recessive character with the same letter, but lower case. For example, if black is dominant over white, we can call N the color black and n the color white.
  • The cross between the two parents is represented by putting the genotype of the parents (the two alleles, first the dominant one if it is a heterozygous individual), and between them an x. For example, Aa x Aa, indicates the cross between two individuals heterozygous for that trait.
  • We indicate the possible gametes (always haploid) that each parent can contribute to their descendants. In the example, each parent will contribute gametes with A and others with a .
  • It will be necessary to observe the possible unions that can occur between the gametes of each of the parents. When the problem is complicated, it is advisable to make a Punnet chart in which we see all the possible unions between the gametes contributed by the parents .
  • In the Punnet chart, all possible genotypes and phenotypes resulting from the cross we are analyzing can be observed. In solving the problem, it will always be necessary to indicate the genotypes and phenotypes obtained, unless they ask otherwise.

Take a good look at how they solve the problems in the following videos because in the following pages you will be the one to solve them.

Genetics problem solved. Mendel's 1st Law

What offspring will be obtained if we cross two purebred pea plants, one with a high stem, with another with a short stem? The tall stem allele is dominant over the short stem allele.

Genetics problem solved. Mendel's Second Law

Now we will see what result we will obtain when crossing the heterozygous descendants originating from the crossing of two pure races ( homozygous  dominant and recessive, respectively).


Intermediate dominance (problem solved)

A gray-winged butterfly is crossed with a black-winged one and a progeny is obtained consisting of 116 black-winged butterflies and 115 gray-winged butterflies. If the gray-winged butterfly is crossed with a white-winged butterfly, 93 white-winged butterflies and 94 gray-winged butterflies are obtained.
Reason for both crosses, indicating the genotypes of the butterflies that are crossed and of the offspring.

Now it's your turn to work. Below you have a collection of solved genetic problems that will allow you to practice in an interactive way.

The problems have been divided according to type. To make the collection of problems more manageable, each category has been divided into pages of up to 10 problems.