Clinical genomics. Textbook of Family Medicine. Philadelphia, PA: Elsevier Saunders; chap Human genetics and patterns of inheritance. Philadelphia, PA: Elsevier; chap 1. Korf BR. Principles of genetics. Goldman-Cecil Medicine. Philadelphia, PA: Elsevier; chap Updated by: Anna C. Review provided by VeriMed Healthcare Network. Variations of dominance highlight the complexity of understanding genetic influences on phenotypes.
Murfet, I. Flowering in Pisum : Multiple alleles at the Lf locus. 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. It depends on how you look at it. If we look at the proteins the two alleles code for, the picture becomes a little more clear.
The affected protein is hemoglobin, the oxygen-carrying molecule that fills red blood cells. The sickle-cell allele codes for a slightly modified version of the hemoglobin protein. The modified hemoglobin protein still carries oxygen, but under low-oxygen conditions the proteins stick together. When a person has two sickle cell alleles, all of their hemoglobin is the sticky form, and the proteins form very long, stiff fibers that distort red blood cells.
When someone has one sickle-cell allele and one normal allele, only some of the hemoglobin is sticky. Non-sticky hemoglobin is made from the normal allele, and sticky hemoglobin is made from the sickle-cell allele every cell has a copy of both alleles. The protist that causes malaria grows and reproduces in red blood cells.
Just exactly how the sickle-cell allele leads to malaria resistance is complex and not completely understood. However, it appears that the parasite reproduces more slowly in blood cells that have some modified hemoglobin. And infected cells, because they easily become misshapen, are more quickly removed from circulation and destroyed.
To see more examples of how variations in genes influence traits, visit The Outcome of Mutation. Dominant and recessive are important concepts, but they are so often over-emphasized. After all, most traits have complex, unpredictable inheritance patterns. However, at the risk of adding even more over-emphasis, here are some more things you may want to know:. Looking at this, you might conclude that the dominant phenotype is twice as common as the recessive one.
But you would probably be wrong. Recessive alleles can be present in a population at very high frequency. Consider eye color. Eye color is influenced mainly by two genes, with smaller contributions from several others. People with light eyes tend to carry recessive alleles of the major genes; people with dark eyes tend to carry dominant alleles. In Scandinavia, most people have light eyes—the recessive alleles of these genes are much more common here than the dominant ones.
Mode of inheritance has nothing to do with whether an allele benefits an individual or not.
0コメント