The father of genetics, Gregor Mendel, first began studying patterns of inheritance using garden-variety pea plants back in the 1800s. Today, his findings have provided the groundwork necessary for the science of genetics to prosper.
Mendel's discoveries established basic rules for genetic principles and inheritance patterns. Understanding the concepts of genotypes and phenotypes is necessary to master Mendelian rules. Though these terms may be unfamiliar, each has a simple explanation.
A phenotype is nothing more than the manner in which a gene is expressed. For example, a dimpled chin is a widely recognized example of a genetic trait. Whether or not you have a dimpled chin determines your phenotype. In other words, if you have a dimple in your chin, the trait is expressed. This also means the trait is dominant. A trait that is hidden, no dimpled chin for example, is what is known as a recessive trait.
A genotype, on the other hand, is the actual hereditary information of an individual. This means that a genotype represents both copies of the alleles one inherits for a particular trait. Remember, a person inherits two copies of a particular gene -- one from each parent.
Dominance rules in patterns of inheritance are pretty straightforward. If an individual inherits two recessive alleles, the trait will always be hidden or masked. This individual would be considered a recessive homozygote.
Recessive alleles are typically indicated with lowercase letters. So, if we say the trait for dimpled chin is represented by a lowercase letter d, then an individual who inherits two recessive alleles, one that came from each parent, will have the dd genotype. Again, someone with this genotype is said to be a recessive homozygote.
Accordingly, if a person receives two copies of a dominant allele, the trait will always be expressed. The expression of two dominant alleles is termed homozygous dominant. Dominant alleles are typically indicated by, you guessed it, capital letters; thus, an individual who has two dominant alleles, DD, for the dimpled chin trait will absolutely have a dimpled chin.
So, if an individual has the genotype of Dd, this means they inherited one dominant and one recessive allele. This person would also be what is known as heterozygous for the trait and they will always express it. The rationale is that dominant alleles are precisely that -- dominant. Even inherited with a recessive allele, a dominant trait will without question be expressed.
Another fascinating feature of recessive traits is that they hold more significance than merely being hidden. In certain cases, inheriting two copies of a recessive allele may indicate that a person will have a particular genetic disease. A few common recessive inherited disorders are Sickle Cell Anemia, Tay Sachs, and Cystic Fibrosis.
These examples are known as autosomal disorders, or diseases linked to the 22 pairs of chromosomes that do not determine gender. Also interesting is that there are dominant inherited disorders which are highly lethal and X- or Y-linked disorders related to mutations in genes located on our sex-determining chromosomes.
Blood type is a unique type of genetic trait which is governed by multiple alleles. Often spoken of as the ABO blood group, these three alleles, A, B, and O, can yield a possible four phenotypes and six different genotypes. In the ABO blood group, A and B are permanently dominant to O.
Furthermore, A and B are codominant meaning if inherited together, both will be expressed. As in any inherited trait, only one allele will come from each parent. The possible combinations are AO, AA, BO, BB, OO, and AB. The phenotypes that result are type A blood for AO and AA genotypes, type B blood for BO and BB genotypes, type O blood for the OO genotype, and type AB blood for the AB genotype. - 16928
Mendel's discoveries established basic rules for genetic principles and inheritance patterns. Understanding the concepts of genotypes and phenotypes is necessary to master Mendelian rules. Though these terms may be unfamiliar, each has a simple explanation.
A phenotype is nothing more than the manner in which a gene is expressed. For example, a dimpled chin is a widely recognized example of a genetic trait. Whether or not you have a dimpled chin determines your phenotype. In other words, if you have a dimple in your chin, the trait is expressed. This also means the trait is dominant. A trait that is hidden, no dimpled chin for example, is what is known as a recessive trait.
A genotype, on the other hand, is the actual hereditary information of an individual. This means that a genotype represents both copies of the alleles one inherits for a particular trait. Remember, a person inherits two copies of a particular gene -- one from each parent.
Dominance rules in patterns of inheritance are pretty straightforward. If an individual inherits two recessive alleles, the trait will always be hidden or masked. This individual would be considered a recessive homozygote.
Recessive alleles are typically indicated with lowercase letters. So, if we say the trait for dimpled chin is represented by a lowercase letter d, then an individual who inherits two recessive alleles, one that came from each parent, will have the dd genotype. Again, someone with this genotype is said to be a recessive homozygote.
Accordingly, if a person receives two copies of a dominant allele, the trait will always be expressed. The expression of two dominant alleles is termed homozygous dominant. Dominant alleles are typically indicated by, you guessed it, capital letters; thus, an individual who has two dominant alleles, DD, for the dimpled chin trait will absolutely have a dimpled chin.
So, if an individual has the genotype of Dd, this means they inherited one dominant and one recessive allele. This person would also be what is known as heterozygous for the trait and they will always express it. The rationale is that dominant alleles are precisely that -- dominant. Even inherited with a recessive allele, a dominant trait will without question be expressed.
Another fascinating feature of recessive traits is that they hold more significance than merely being hidden. In certain cases, inheriting two copies of a recessive allele may indicate that a person will have a particular genetic disease. A few common recessive inherited disorders are Sickle Cell Anemia, Tay Sachs, and Cystic Fibrosis.
These examples are known as autosomal disorders, or diseases linked to the 22 pairs of chromosomes that do not determine gender. Also interesting is that there are dominant inherited disorders which are highly lethal and X- or Y-linked disorders related to mutations in genes located on our sex-determining chromosomes.
Blood type is a unique type of genetic trait which is governed by multiple alleles. Often spoken of as the ABO blood group, these three alleles, A, B, and O, can yield a possible four phenotypes and six different genotypes. In the ABO blood group, A and B are permanently dominant to O.
Furthermore, A and B are codominant meaning if inherited together, both will be expressed. As in any inherited trait, only one allele will come from each parent. The possible combinations are AO, AA, BO, BB, OO, and AB. The phenotypes that result are type A blood for AO and AA genotypes, type B blood for BO and BB genotypes, type O blood for the OO genotype, and type AB blood for the AB genotype. - 16928
About the Author:
RJ Sullivan manages several profitable online businesses and is an accomplished editor and writer. Ms. Sullivan also writes for In the Gno, a blog dedicated to presenting the science of genetics in an interesting and easy-to-understand manner. Visit her blog to learn more about mendelian genetics or blood types.
No comments:
Post a Comment