dominant or recessive
Genes are the chemical factors that determine traits, but alleles are the different forms of the gene. An allele is used to describe the
genes that express or do not express a specific trait. For example, if we're looking at eye color, there is an allele for blue eyes and an allele for brown eyes. An allele as written as two letters with each letter describing the trait. In this case, the letters for brown eyes or blue eyes could be B and b respectively. the reason why brown gets a capital B and blue gets a lowercase b is because the allele for brown eyes is dominant over the allele for blue eyes.
The Principle of Dominance states that some alleles are dominant and others are recessive. Both dominant and recessive traits have the ability to be expressed. The principle of dominance merely means that recessive traits will not be expressed when an allele for the dominant trait is present.
How you write down a persons genotype for a specific trait depends on wether they have dominant or recessive alleles. If a person has all dominant and no recessive alleles, their genotype would be written as two capital letters, like BB. this person would be homozygous dominant. If a person has all recessive and no dominant alleles, their genotype would be written as two lowercase letters, like bb, and they are considered homozygous recessive. If a person has one dominant allele and one recessive allele, that genotype would be written as one capital and one lowercase letter, like Bb, and they are heterozygous dominant.
genes that express or do not express a specific trait. For example, if we're looking at eye color, there is an allele for blue eyes and an allele for brown eyes. An allele as written as two letters with each letter describing the trait. In this case, the letters for brown eyes or blue eyes could be B and b respectively. the reason why brown gets a capital B and blue gets a lowercase b is because the allele for brown eyes is dominant over the allele for blue eyes.
The Principle of Dominance states that some alleles are dominant and others are recessive. Both dominant and recessive traits have the ability to be expressed. The principle of dominance merely means that recessive traits will not be expressed when an allele for the dominant trait is present.
How you write down a persons genotype for a specific trait depends on wether they have dominant or recessive alleles. If a person has all dominant and no recessive alleles, their genotype would be written as two capital letters, like BB. this person would be homozygous dominant. If a person has all recessive and no dominant alleles, their genotype would be written as two lowercase letters, like bb, and they are considered homozygous recessive. If a person has one dominant allele and one recessive allele, that genotype would be written as one capital and one lowercase letter, like Bb, and they are heterozygous dominant.
Let's look at the image to the left for reference, which shows all the possible genotypes and phenotypes of a couple's child. As you can see, even though the father carries both an allele for brown eyes (B) and an allele for blue eyes (b) the phenotype he is expressing is brown. However, that recessive allele for blue eyes is still there and can still be passed onto his offspring. The case is the same for the mother.
The first possible offspring from the left has a genotype of BB, meaning that this child would not inherit any blue eye genes from his/her mother or father. The second two possible offspring have genotypes of Bb. This means that they, like their parents, would express the dominant B allele while still carrying the recessive b allele. The third possible offspring's genotype is bb. This child would not inherit any of the dominant B alleles from his/her parents, which is much less common. This child only has recessive b alleles and no dominant B alleles, so it's phenotype is having blue eyes.
image source: http://carrier.pbworks.com
If you want to know the probability of an offspring inheriting a trait from its parents, you can find it out by using a punnet square. There is also something called incomplete dominance, where one allele for a specific trait is not completely dominant over the other allele. This results in a combined phenotype. You can learn more about incomplete dominance here.
The first possible offspring from the left has a genotype of BB, meaning that this child would not inherit any blue eye genes from his/her mother or father. The second two possible offspring have genotypes of Bb. This means that they, like their parents, would express the dominant B allele while still carrying the recessive b allele. The third possible offspring's genotype is bb. This child would not inherit any of the dominant B alleles from his/her parents, which is much less common. This child only has recessive b alleles and no dominant B alleles, so it's phenotype is having blue eyes.
image source: http://carrier.pbworks.com
If you want to know the probability of an offspring inheriting a trait from its parents, you can find it out by using a punnet square. There is also something called incomplete dominance, where one allele for a specific trait is not completely dominant over the other allele. This results in a combined phenotype. You can learn more about incomplete dominance here.