Cycle 5

Gregor Mendel

A scientist known for his quantitative approach to science and statistical analysis in the study of genetics.

Explanatory Model

The idea that variation in traits is due to different alleles, and organisms inherit two alleles for each trait, one from each parent. The phenotype is determined by the dominant allele, and the frequency of alleles is determined by selection rather than dominance.

Principle of Segregation

The principle that two alleles of a gene segregate from each other in gamete formation, with one allele on each chromosome.

Principle of Independent Assortment

The principle that during the segregation of alleles into gametes, the alleles of different gene pairs assort independently, randomly lining up along the metaphase plate.

Monohybrid Cross

A cross that involves one character, resulting in a 3:1 phenotypic ratio. It creates two gametes.

Dihybrid Cross

A cross involving two characters, resulting in a 9:3:3:1 phenotypic ratio. It creates four gametes.

Testcross

A cross involving one homozygous recessive parent and another unknown parent, used to determine whether the genotype of the second parent is heterozygous or homozygous.

Sex Linked Genes (Reciprocal Cross)

Genes that are inherited differently in males and females, with only males receiving the Y chromosome. Sex-linked traits are not carried on the Y chromosome.

Locus (Loci)

A particular site on a chromosome where a gene is located.

Alleles

Multiple forms of a gene that result in functional differences in the protein or RNA product encoded by the gene.

Sum Rule

The probability that either event A or event B will occur is obtained by adding the fractions.

Product Rule

The probability that events A and B both will occur is obtained by multiplying the fractions.

Epistasis

The interaction of genes at one locus inhibiting the effects of alleles at a different locus, resulting in some expected phenotypes not appearing among offspring.

Codominance

When alleles have approximately equal effects in individuals, making both phenotypes equally detectable in heterozygotes.

Incomplete Dominance

When the effects of recessive alleles can be detected to some extent in heterozygotes, resulting in a blending of the phenotypes.

Polygenic Traits

Traits that are influenced by many different genes.

Pleiotropic Genes

Genes that affect more than one character of an organism.

Quantitative Traits

Traits that display a continuous distribution of the phenotype involved, often following a bell curve.

X-linked Inactivation

The process in females with two X chromosomes where most of the genes on one X chromosome are inactivated in most body cells, resulting in a mosaic-like pattern of gene expression.