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| Gregor Mendel | He is a monk in the 19th century who is considered the father of genetics. Much of what we know about genetics today was discovered by him. |
| Trait | It is an expressed characteristic. It is produced by hereditary factors known as genes. |
| Gene | It is a segment of a chromosome. In each chromosome, there are many different genes controlling the expression of particular traits. |
| Locus | It is the position of a gene on a chromosome. |
| Allele | It is the alternate form of the same gene. In diploid organisms (two sets of chromosomes), there are usually two copies of one gene and they might be alleles. |
| Dominant Allele | This means that the if this allele was in an organism, it would be expressed, even if the other (recessive) allele was also present. The dominant allele is represented by a capital letter. In pea plants, the allele tall would be T. |
| Recessive Allele | It is the opposite of the dominant allele. It is represented by the lower case of the same letter as the dominant. In pea plants, the recessive allele for short is represented by t. |
| Homozygous | It is when an organism has two identical alleles for a given trait. The organism can have homozygous dominant (TT) and homozygous recessive (tt). |
| Heterozygous | This is when the organism has two different alleles for a given trait (Tt). |
| Mendelian Genetics | Mendel liked to cross-breed pea plants. Through his work, he came up with three principles: law of dominance, law of segregation and law of independent assortment. |
| The Law of Dominance | When Mendel cross-bred a homozygous dominant plant that was tall with a homozygous recessive plant that was short, it produced a tall plant (the phenotype was still tall). This is because the dominant gene masked the recessive gene. |
| Phenotype | This is the physical appearance of an organism. It is what an organism looks like. |
| Genotype | It refers to the genetic makeup of an organism. It is which alleles the organism posses. |
| Parent (P1 Generation) | These are the first generation in an experiment. |
| Filial (F1 Generation) | The offspring of the P1 generation are called filial and are represented by F1. |
| F2 Generation | This is the grandchildren of the parent and the offspring of the F1 generation. |
| Monohybrid Cross | This is a cross where only one trait is being studied. It is easily shown through a Punnett square. |
| Punnett Square | It is used to predict the results of a cross. |
| The Law of Segregation | It states that the alleles separate randomly during meiosis and are paired randomly during sexual reproduction and thus will produce different results. |
| Dihybrid Cross | This is where two characteristics are studied as opposed to one. It can also be represented by a Punnett Square. |
| Independent Assortment | It states that each trait segregate independently from each other and thus are usually not affected by the outcome of the other. When predicting the likelihood of certain results, we should use probability in which we multiply the different possibilities. |
| Test Cross | To determine if an organism is heterozygous or homozygous dominant, we can set up a test cross in which we cross the unknown organism with a homozygous recessive. If a recessive organism is an offspring, then the unknown is heterozygous, otherwise, it's homozygous dominant. |
| Incomplete Dominance | In some cases, the traits will blend. For example, a cross between a white snapdragon (dominant) and a red snapdragon (recessive) produces a pink snapdragon. |
| Codominance | It is the equal expression of both alleles. For example, an individual can have an AB type blood where each allele is equally expressed. |
| Polygenetic Inheritence | Sometimes, one trait results from many different genes acting together. Height, skin colour, and weight are all examples. |
| Multiple Alleles | Some traits are the product of many different alleles that occupy the same specific locus. The ABO blood group system has three alleles which determines blood type. |
| Epitasis | This is when the gene at one locus influences the expression of a gene at another locus. |
| Pleiotropy | It is when an allele affects numerous characteristics of an organism. In sickle-cell anemia, multiple symptoms are caused by one pair of alleles. |
| Linked Genes | Sometimes genes on the same chromosomes stay together during assortment and move as a group. They are usually inherited together. This can be used to map human chromosomes. |
| Recombination Mapping | Because the further apart two linked alleles are on a chromosome, the higher the frequency of them meeting. And thus this can be used to map chromosomes. If A and B have a frequency of 15 , B and C have a frequency of 9 and A and C have a frequency of 24, we can now map all three alleles. A ______________B________C |
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