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Single-gene disorder
Hereditary disorder caused by a mutant allele of a single gene.
Centromere
A specialized chromosome region to which spindle fibers attach during cell division.
Identical twin
Twins produced by the division of a single zygote; both have identical genotypes.
Junk DNA
Stretches of DNA that do not code for genes; most of the genome consists of so-called junk DNA which may have regulatory and other functions.
Mutation
Any heritable change in DNA sequence.
Fraternal twin
Siblings born at the same time as the result of fertilization of two ova by two sperm. They share the same genetic relationship to each other as any other siblings.
Haploid
A single set of chromosomes (half the full set of genetic material) present in the egg and sperm cells of animals and in the egg and pollen cells of plants
Gene
The fundamental physical and functional unit of heredity. A gene is an ordered sequence of nucleotides located in a particular position on a particular chromosome that encodes a specific functional product
Birth defect
Any harmful trait, physical or biochemical, present at birth, whether a result of a genetic mutation or some other nongenetic factor.
Hybrid
The offspring of genetically different parents.
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