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Autosomal dominant and autosomal recessive inheritance, the two most common Mendelian inheritance patterns. An autosome is any chromosome other than a sex chromosome.. In genetics, dominance is the phenomenon of one variant of a gene on a chromosome masking or overriding the effect of a different variant of the same gene on the other copy of the chromosome.
The letters B and b represent alleles for colour and the pictures show the resultant flowers. The diagram shows the cross between two heterozygous parents where B represents the dominant allele (purple) and b represents the recessive allele (white). Traits that are determined exclusively by genotype are typically inherited in a Mendelian pattern.
An allele [1], or allelomorph, is a variant of the sequence of nucleotides at a particular location, or locus, on a DNA molecule. [ 2 ] Alleles can differ at a single position through single nucleotide polymorphisms (SNP), [ 3 ] but they can also have insertions and deletions of up to several thousand base pairs .
An individual that is homozygous-dominant for a particular trait carries two copies of the allele that codes for the dominant trait. This allele, often called the "dominant allele", is normally represented by the uppercase form of the letter used for the corresponding recessive trait (such as "P" for the dominant allele producing purple flowers ...
Selected portions of the DNA nucleotide sequence are copied into a corresponding RNA nucleotide sequence, which either encodes a protein (if it is an mRNA) or forms a 'structural' RNA, such as a transfer RNA (tRNA) or ribosomal RNA (rRNA) molecule. Each region of the DNA helix that produces a functional RNA molecule constitutes a gene. [15]
The hair color of these children depends on how these alleles work together. If one allele dominates the instructions from another, it is called the dominant allele, and the allele that is overridden is called the recessive allele. In the case of a daughter with alleles for both red and brown hair, brown is dominant and she ends up with brown hair.
Offspring with either one or two copies of the dominant allele will display the dominant phenotype. Very few phenotypes are purely Mendelian traits. Common violations of the Mendelian model include incomplete dominance , codominance , genetic linkage , environmental effects , and quantitative contributions from a number of genes (see: gene ...
Markers can exhibit two modes of inheritance, i.e. dominant/recessive or co-dominant. If the genetic pattern of homo-zygotes can be distinguished from that of hetero-zygotes, then a marker is said to be co-dominant. Generally co-dominant markers are more informative than the dominant markers. [3]