Genetics the same recessive allele. Heterozygous means

Genetics is the study of heredity and helps better our understanding and treatment of various disorders. Roughly, we have 37.2 trillion cells in our bodies, and each cell contains a complete copy of our genetic information, DNA. DNA is Deoxyribonucleic acid which occurs as a thread-like chain un organised in the cell nucleus. A known segment of a DNA is known as a gene which determines traits such as eye colour or height. “Our DNA contains the instructions for growth and development and is packaged into chromosomes that contain all our genes” (studylib, 2017).

In each one of our cells (apart from red blood cells) there are 46 chromosomes making up 23 pairs of homologous chromosomes. The 23rd pair are the sex chromosomes, which are responsible for x-linked dominant and recessive inheritance. Chromosome pairs 1-22 are the autosomes, which are responsible for autosomal dominant and recessive inheritance. An Allele is a variant of a gene. “An organism can be homozygous dominant, if it carries two copies of the same dominant allele, or homozygous recessive, if it carries two copies of the same recessive allele.

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Heterozygous means that an organism has two different alleles of a gene.” (, 2017). Humans are called diploid organisms because they have two chromosomes; one inherited from each parent.

The chromosomes from each parent make up our genotype for specific genes. A phenotype is an “observable characteristics of an individual resulting from the interaction of its genotype with the environment” (, 2017).

In reference to above, “the interaction of its genotype” depends on whether the alleles are dominant, recessive, codominant or incomplete dominance in turn deciding what the phenotype will be for that particular trait. Furthermore, a dominant allele will mask a recessive allele making the phenotype the dominant allele. A recessive allele will become the phenotype only when paired with another recessive allele. Codominance occurs when both alleles are expressed. Incomplete dominance occurs when when one allele is not completely dominant over another (They blend).

Pedigree diagrams uses special symbols to represent the individuals in a family and track a particular genetic trait in that family. Genetic Counsellors use pedigree diagrams to track Huntington’s Disease. Punnett squares are used to predict a genotype in the progeny when breeding. Pathogenic variants or other known as a mutation, occurs when a cell reproduces by copying its genetic information then splitting in half, forming two individual cells. Occasionally, a fault is made causing an alteration in the DNA sequence (genetic mutation). These mutations can disrupt the accepted patterns of inheritance.

It was originally thought that eye color was a simple Mendelian trait, meaning it was determined by a single gene, with brown being dominant and blue recessive. New research proves that eye color is a polygenic trait, meaning it is determined by multiple genes. Two main genes that control the phenotype of blue eyes.


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