Genetics Vocabulary

  • Genetics Vocabulary


    1. Genetics :  the study of how traits are passed from one generation to the next.


    1. Reproduction : a process that produces a new generation of offspring.


    1. Gregor Mendel: the “father of genetics”; he discovered most of principles of heredity while studying pea plants.


    1. Trait : an observable characteristic – like hair color, presence of scales, or height - that is passed from one generation to the next.


    1. Heredity:  the passing of traits from parent generations to offspring generations.


    1. Chromosome : a thread-like structure in the nucleus of a cell that controls heredity.  Chromosomes are made up of DNA, which makes the code for various genes. 


    1. Homologous Chromosomes:  These are chromosome pairs that contain genes for the same characteristics.  An organism gets one of these chromosomes from its mother and the other from its father.  Humans have  23 chromosome pairs.  22 of these pairs are homologous chromosomes.  The last chromosome pair is made up of the sex chromosomes, (either xx or xy) which determines the gender of the person.


    1. Gene:  A piece of DNA that carries the genetic information to control one trait.  Each gene has a specific location on a specific pair of chromosomes.


    1. Allele:  A version of a gene;  each gene may have more than one version.  For example, for height of pea plants there is a tall gene and a short gene.  Tall and short are the alleles for height.  Each parent gives their offspring one allele for each gene.


    1. Deoxyribonucleic Acid or DNA :  the chemical in chromosomes that contains the genetic code for heredity.  It is shaped like a double helix (a twisted ladder shape).  The structure of DNA was discovered by James Watson, Francis Crick, Maurice Wilkins, and Rosiland Franklin.


    1. Nucleus : a cell organelle that stores chromosomes.


    1.  Genotype:  The specific genes that an organism has for a given trait.  When writing out genotypes, Alleles are represented by individual letters.  A capital letter is used to represent a dominant gene, and a lower cased letter is used to represent a recessive gene.

    Ex:  If a pea plant had a genotype of Tt for height, it would have one dominant gene (tall)  

            and one recessive gene (short) for height.


    1. Phenotype:  The physical appearance of an organism (how they look) for a given trait. 

    Ex:  Curly hair or having a widows peak


    1. Dominant gene : It will show up in an offspring that gets that gene;  a gene that is able to “cover up” a recessive gene so that the dominant gene shows up in an organism’s phenotype when the organism is heterozygous for a trait.    It is represented by a capital letter.


    1.  Recessive gene :  A gene that can be “covered up” by a dominant gene.  It will get masked in a heterozygous / hybrid offspring with that gene.  The only way that a recessive gene will show up in an organism’s phenotype is:

    a)       If the organism has 2 copies of the recessive gene

    b)      If the organism inherited one copy of the gene, but there is no dominant gene present to “cover up” the recessive gene.

    Recessive genes are represented by a lower case letter.


    1. Homozygous or purebred:  When an organism has two of the same genes/ alleles for a given trait.


    1. Heterozygous or hybrid:  When an organism has two different genes/ alleles for a given trait


    1. Gamete : a  sex cell (sperm or egg cell).


    1. Fertilization: occurs when a sperm cell unites with an egg cell.


    1. Sexual reproduction: requires two sets of DNA, one set from each of two parents, combining to produce an offspring.  Offspring will have a combination of traits from both parents, and will not look exactly like either parent


    1. Asexual reproduction: only requires one set DNA from one parent to produce an offspring.  All offspring will be identical to the original parent.


    1. Cell division: the process by which cells reproduce.


    1. Mitosis : cell division where one cell splits into two daughter cells that are identical to the original cell.  Mitosis is responsible for growth and repair of organisms.


    1. Meiosis:  the process by which gametes are made.  It involves one germ cell splitting  into four gametes during the making of sperm.  When egg cells are made, one germ cell ends up splitting into 1 egg cell and 3 polar bodies.


    1. Variation: is the genetic differences between individuals of the same species that are caused during sexual reproduction, by mutation or as a result of natural selection.  Variation within a species is a good thing – it increases the chance that a species will be able to survive if there is a major climate change or an epidemic of some type of disease that the species is vulnerable to.


    1. X/Y chromosomes: control the trait related to the gender of an offspring.


    1. Mutation: a variation caused by a misspelling in the DNA of an organism.  Mutations can arise naturally due to chance, they may be caused by several factors including exposure to radiation or chemicals.


    1. Extinction: occurs when the last of species dies because it didn’t adapt to changes in the environment.


    1. Competition: is trying hard to fulfill needs from limited resources over rival organisms in an effort to ensure survival.


    1. Natural selection:  the process where nature eliminates organisms that don’t adapt to a changing environment or can’t compete for limited resources.


    1. Pedigree chart:  a graphic family history that shows how a trait has been passed from generation to generation.


    1. Punnett square: uses parent’s genes to help predict the chances of a trait being exhibited in an offspring.