Why are heterozygous individuals generally healthy

For example, being heterozygous for hair color could mean you have one allele for red hair and one allele for brown hair. The relationship between the two alleles affects which traits are expressed. It means your biological parents contributed identical variants.

In this scenario, you may have two normal alleles or two mutated alleles. Mutated alleles can result in a disease and will be discussed later. This also affects which characteristics appear. In a heterozygous genotype, the two different alleles interact with each other.

This determines how their traits are expressed. Commonly, this interaction is based on dominance. Depending on how the dominant and recessive genes interact, a heterozygous genotype might involve:. In complete dominance, the dominant allele completely covers up the recessive one. One example is eye color , which is controlled by several genes. The allele for brown eyes is dominant to the one for blue eyes.

However, you still have the recessive allele for blue eyes. Instead, they blend together, which creates a third trait. This type of dominance is often seen in hair texture. The waviness is a combination of curly and straight hair. Codominance happens when the two alleles are represented at the same time. Both traits are equally expressed. An example of codominance is the AB blood type. In this case, you have one allele for type A blood and one for type B. Instead of blending and creating a third type, both alleles make both types of blood.

Heredity 35 , 85—98 Parsons, P. The evolution of overdominance: Natural selection and heterozygote advantage. Nature , 7—12 link to article. Stratton, F. The human blood groups. Nature , link to article. Chromosome Theory and the Castle and Morgan Debate. Discovery and Types of Genetic Linkage. Genetics and Statistical Analysis. Thomas Hunt Morgan and Sex Linkage. Developing the Chromosome Theory. Genetic Recombination.

Gregor Mendel and the Principles of Inheritance. Mitosis, Meiosis, and Inheritance. Multifactorial Inheritance and Genetic Disease. Non-nuclear Genes and Their Inheritance. Polygenic Inheritance and Gene Mapping. Sex Chromosomes and Sex Determination. Sex Determination in Honeybees. Test Crosses. Biological Complexity and Integrative Levels of Organization. Genetics of Dog Breeding. Human Evolutionary Tree. Mendelian Ratios and Lethal Genes.

Environmental Influences on Gene Expression. Epistasis: Gene Interaction and Phenotype Effects. Genetic Dominance: Genotype-Phenotype Relationships. Phenotype Variability: Penetrance and Expressivity. Citation: Miko, I. Nature Education 1 1 Why can you possess traits neither of your parents have? The relationship of genotype to phenotype is rarely as simple as the dominant and recessive patterns described by Mendel.

Aa Aa Aa. Complete versus Partial Dominance. Figure 1. Figure Detail. Multiple Alleles and Dominance Series. Summarizing the Role of Dominance and Recessivity. References and Recommended Reading Keeton, W. Heredity 35 , 85—98 Parsons, P. Nature , 7—12 link to article Stratton, F. Article History Close. Share Cancel. Revoke Cancel.

Keywords Keywords for this Article. Save Cancel. Flag Inappropriate The Content is: Objectionable. Assume that red is totally recessive. Please calculate the following: The allele frequencies of each allele. Therefore, q the square root of q 2 is 0.

The expected genotype frequencies. The number of heterozygous individuals that you would predict to be in this population. Answer: That would be 0. The expected phenotype frequencies.

Conditions happen to be really good this year for breeding and next year there are 1, young "potential" Biology instructors. Assuming that all of the Hardy-Weinberg conditions are met, how many of these would you expect to be red-sided and how many tan-sided? White coloring is caused by the double recessive genotype, "aa".

Calculate allelic and genotypic frequencies for this population. The square root of 0. Now that we know the frequency of each allele, we can calculate the frequency of the remaining genotypes in the population AA and Aa individuals.

If you add up all these genotype frequencies, they should equal 1. After graduation, you and 19 of your closest friends lets say 10 males and 10 females charter a plane to go on a round-the-world tour. Unfortunately, you all crash land safely on a deserted island. No one finds you and you start a new population totally isolated from the rest of the world. Two of your friends carry i. Assuming that the frequency of this allele does not change as the population grows, what will be the incidence of cystic fibrosis on your island?

Answer: There are 40 total alleles in the 20 people of which 2 alleles are for cystic fibrous. That represents p. You sample 1, individuals from a large population for the MN blood group, which can easily be measured since co-dominance is involved i. Supposing the matings are random, the frequencies of the matings.

Answer: This is a little harder to figure out. Try setting up a "Punnett square" type arrangement using the 3 genotypes and multiplying the numbers in a manner something like this: MM 0. Thus, three of the possibilities must be doubled. Cystic fibrosis is a recessive condition that affects about 1 in 2, babies in the Caucasian population of the United States.