2nd October 2019
What does it mean for an allele to be dominant over another allele?
The simplest situation of dominant and recessive alleles is if one allele makes a broken protein. When this happens, the working protein is usually dominant. The broken protein doesn't do anything, so the working protein wins out. If both copies of your MC1R gene code for broken proteins, then you'll have red hair.
Can a person have two dominant alleles?
Organisms that reproduce sexually have two copies of each gene, one from each parent. These matching gene pairs are called alleles. The alleles are homozygous if they code for the same trait and heterozygous if they code for different traits. A homozygous pair might have two dominant or two recessive alleles.
Recessive and dominant alleles. You will recall that genes have different forms called alleles. An allele can be recessive or dominant. A recessive allele only shows if the individual has two copies of the recessive allele.
The two copies, called alleles, can be slightly different from each other. For a recessive allele to produce a recessive phenotype, the individual must have two copies, one from each parent. An individual with one dominant and one recessive allele for a gene will have the dominant phenotype.
This is the underlying reason why red hair is a recessive trait. The other copy can independently make enough working protein to do its job and keep red hair at bay. Because of how red hair versions of the MC1R gene work, they can't simply become dominant. To get dominant red hair, we'll need a new DNA difference.
The other gene, weaker and usually hidden by the stronger gene, was called the recessive gene for that trait. If an offspring receives two of the same genes (either two dominant genes or two recessive genes) the offspring will inherit or have that trait. Pure traits can be either recessive or dominant.
In biology, we call traits “alleles”. Things like “I have blue eyes” or “my blood cells do not function properly” are traits. Traits are caused by genes. Traits that only require one copy of the same gene to show up are called “dominant” while traits that require two copies of the same gene are called “recessive.”
When a single copy of a disease allele doesn't result in a disease but instead is good for the person or organism that carries it, we say that allele has a heterozygote advantage. One example is sickle cell trait, which protects against malaria in heterozygotes, but causes a deadly disease in homozygotes.
The brown version of gene 1 is dominant over the blue one. The way geneticists represent these two different versions of this eye color gene are B for brown and b for blue (the capital letter is always the dominant, the lowercase, the recessive). So you will have brown eyes with either BB or Bb and blue eyes with bb.
Only individuals with an aa genotype will express a recessive trait; therefore, offspring must receive one recessive allele from each parent to exhibit a recessive trait. One example of a recessive inherited trait is a smooth chin, as opposed to a dominant cleft chin.
allele. An allele is a variant form of a gene. Some genes have a variety of different forms, which are located at the same position, or genetic locus, on a chromosome. Humans are called diploid organisms because they have two alleles at each genetic locus, with one allele inherited from each parent.
Examples of Incomplete Dominance. Pink roses are often the result of incomplete dominance. When red roses, which contain the dominant red allele, are mated with white roses, which is recessive, the offspring will be heterozygotes and will express a pink phenotype.
Examples of incomplete dominance are: A snapdragon flower that is pink as a result of cross-pollination between a red flower and a white flower when neither the white or the red alleles are dominant.
codominant. Not all alleles are dominant and recessive like the ones Mendel studied in his pea plants. Some alleles are equally strong and neither are masked by the other. When both alleles are present, they are both expressed in the phenotype.
Examples of codominance include a person with type AB blood, which means that both the A allele and the B allele are equally expressed. Another example is roan fur in cattle, in which white and red hair is equally expressed.
There may be many possible alleles for any gene, but a diploid cell or animal contains only two alleles of each gene or two copies of a single allele; a haploid gamete contains one copy of each gene, so only one allele.
In a diploid organism, one that has two copies of each chromosome, two alleles make up the individual's genotype. An example is the gene for blossom color in many species of flower — a single gene controls the color of the petals, but there may be several different versions (or alleles) of the gene.
Because a gamete, by definition, has only one chromosome for each chromosome pair. So therefore, unless there's a mutation in the chromosome that causes allele duplication, each chromosome in a pair has only one of a given allele.
Inheritance of Traits by Offspring Follows Predictable Rules. Genes come in different varieties, called alleles. Somatic cells contain two alleles for every gene, with one allele provided by each parent of an organism.
meiosis. Meiosis is a type of cell division that reduces the number of chromosomes in the parent cell by half and produces four gamete cells. This process is required to produce egg and sperm cells for sexual reproduction.
Formation of Gametes. Both the male and female gametes are formed during a process of cellular reproduction called meiosis. During meiosis, the DNA is only replicated or copied one time. However, the cells are divided into four separate cells.