Genetics
Genetics is a branch of biology concerned with the study of genes, genetic variation, and heredity in organisms.
Genetics is the study of the inheritance of traits.
Though heredity had been observed for millennia, Gregor Mendel, a scientist and Augustinian friar working in the
19th century (1800´s), was the first to study genetics scientifically. Mendel studied "trait inheritance", patterns in the
way traits are handed down from parents to offspring. He observed that organisms (pea plants) inherit traits by way
of discrete "units of inheritance". This term, still used today, is a somewhat ambiguous definition of what is referred
to as a gene.
Mendelian inheritance is a type of biological inheritance that follows the principles originally proposed by Gregor
Mendel in 1865 and 1866, re-discovered in 1900 and popularized by William Bateson. These principles were initially
controversial.
Non-mendelian inheritance is a type of biological inheritance that doesn’t follows the principles originally proposed
by Gregor Mendel in 1865 and 1866.
Gene A sequence of DNA that codes for a specific protein. Located on the chromosome. Genes are parts of a
chromosome that determine an organism’s traits. Genes occur in pairs, represented as a letter, the upper case
represent a dominant allele and the lower case a recessive allele : AA, Aa, aa, aA each from a parent.
Chromosome Structures that carry the genetic information in the form of DNA molecules.
Allele One of the forms of a gene that controls a particular trait. Most traits are determined by 2 alleles, 1 from each
parent Trait A characteristic of a species determined by specific genes. Alleles are different forms of a trait.
Phenotype The effect caused by a particular set of genes. What is physically seen. Phenotype of an organism is its
appearance. (ex. dimples or no dimples)
Genotype The genes responsible for a specific trait. What you cannot see. Genotype of an organism is its gene
combination. (ex. DD or Dd or dd)
Dominant A gene that always shows itself. The presence of this type of gene will mask the other gene in the allele.
Recessive The phenotype of this gene is only present when the dominant gene in the allele is absent. Recessive traits
sometimes are hidden by another trait.
Homozygous/Purebred When the 2 genes in a pair are identical. Pure for a trait means that both genes inherited for
a trait are the same. (ex. DD or dd)
Heterozygous/Hybrid When the 2 genes in a pair are different Complete Dominance Dominant gene is expressed,
unless not present, then recessive gene is expressed Incomplete Dominance Genes produce a trait somewhere in
between the traits of the 2 parents. Hybrid for a trait means that both genes inherited for a trait are different. (ex.
Dd)
Karyotype: A karyotype is simply a picture of a person's chromosomes. In order to get this picture, the chromosomes
are isolated, stained, and examined under the microscope. Most often, this is done using the chromosomes in the
white blood cells.
Co-Dominance 2 dominant traits are present. When two alleles are both dominant but different from each other.
(Example: AB blood type).
Incomplete dominance: when one allele is not completely dominant over the other, the results is a mix of both
traits. (example: red plus white makes pink flowers).
Polygenic inheritance: when a trait is controlled by more than one gene. Sometimes expressed by the environment
or development of the individual. Example: color of hydrangea is also due to soil ph.
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