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Maxwell Blue's Oubliette: Biology Back to HOME PAGE

Gene: a stretch of DNA that codes for a specific trait (Mendel's 'factors') (e.g., flower color).

Allele: a particular variant of a gene (e.g., if the gene is flower color, purple and white are two separate alleles).

Homologous chromosomes: chromosomes that have the same exact genes but may have different alleles (you have 2 homologues of each of 23 chromosomes, giving you 23 pairs of chromosomes. Mom gives you 23 and Dad gives you the other 23).

Centromere: a region of DNA typically found near the middle of a chromosome where two identical sister chromatids come in contact. It is involved in cell division as the point of mitotic spindle attachment.

Sister Chromatid: two identical chromosomes joined at the centromere (actually they are a single chromosome since they share a centromere)

Genotype: what alleles an individual has for a particular trait or set of traits (e.g., Pp)

Phenotype: the expression of the genes; what the individual looks like (e.g., purple)

Dominant Trait: an allele that is expressed no matter what the other allele is (e.g., purple flower color being dominant to white flower color in pea plants.)

Recessive Trait: an allele that is only expressed if it is the only allele present (i.e., both alleles are the same) (e.g., white flower being recessive to purple flower color.)

F1 Generation: the kids of the parents

F2 Generation: the grandkids of the parents (kids of F1)

Gamete: sex cell (egg or sperm); only has ONE allele for each gene since it only has one homologous chromosome (either the one you received from Mom or the one you received from Dad)

Punnett Square: a diagram that is used to predict an outcome of a particular cross or breeding experiment.

Homozygous: has 2 copies of the same allele for a given trait (e.g., PP)

Heterozygous: has 1 copy of each of two alleles for a given trait (e.g., Pp)

Autosomal: on a normal chromosome (as opposed to the sex-determining chromosome)

Sex-Linked: on the X chromosome (so males only have 1 copy of the gene)

Meiosis: the cellular process that produces gametes (sex cells) in our bodies. It reduces the amount of DNA from 23 pairs of chromosomes to just 23 chromosomes.

Dihybrid Cross: a cross between F1 offspring of two individuals that differ in two traits of particular interest. For example: RRyy/rrYY or RRYY/rryy parents result in F1 offspring that are heterozygous for both R and Y (RrYy).

Law of Segregation: there is an equal probability of each allele being produced in meiosis

Law of Independent Assortment: when two genes are involved (dihybrid cross), the effect of one gene is independent of the effect of the other gene. Note that this law does not work in cases of linkage, since the genes are on the same chromosome.

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Interphase: the phase of the cell cycle in which the cell spends the majority of its time and performs the majority of its purposes including preparation for cell division.

Prophase: stage of mitosis in which the chromatin condenses into a highly ordered structure called a chromosome in which the chromatin becomes visible.

Metaphase: a stage of mitosis in the eukaryotic cell cycle in which condensed & highly coiled chromosomes, carrying genetic information, align in the middle of the cell before being separated into each of the two daughter cells. Metaphase accounts for approximately 4% of the cell cycle's duration.

Anaphase: the stage of mitosis when chromosomes separate in a eukaryotic cell. Each chromatid moves to opposite poles of the cell, the opposite ends of the mitotic spindle, near the microtubule organizing centers.

Telophase: (also known as telephase) is a stage in both meiosis and mitosis in a eukaryotic cell. During telophase, the effects of prophase and prometaphase events are reversed. Two daughter nuclei form in the cell. The nuclear envelopes of the daughter cells are formed from the fragments of the nuclear envelope of the parent cell. As the nuclear envelope forms around each pair of chromatids, the nucleoli reappear.

Cytokinesis: the process in which the cytoplasm of a single eukaryotic cell is divided to form two daughter cells. It usually initiates during the late stages of mitosis, and sometimes meiosis, splitting a binucleate cell in two, to ensure that chromosome number is maintained from one generation to the next.

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Chargaff's rules state that DNA from any cell of all organisms should have a 1:1 ratio of pyrimidine and purine bases and, more specifically, that the amount of guanine is equal to cytosine and the amount of adenine is equal to thymine. This pattern is found in both strands of the DNA. They were discovered by Austrian chemist Erwin Chargaff.

Centrosome: an organelle that serves as the main microtubule organizing center (MTOC) of the animal cell as well as a regulator of cell-cycle progression.

Ploidy, Haploid and monoploid, Diploid

Incomplete dominance: in this case, the presence of a single gene to code for a particular protein (enzyme) is insufficient to produce the full trait.

Test cross: When a single trait is being studied, a test cross is a cross between an individual with the dominant phenotype but of unknown genotype (homozygous or heterozygous) with a homozygous recessive individual. If the unknown is heterozygous, then approximately 50% of the offspring should display the recessive phenotype.

Monohybrid cross: cross between two monohybrids (only a single trait is tracked) (e.g., Pp x Pp)

Dihybrid Cross: cross between two dihybrids (e.g., PpYy x PpYy).

Polygenic traits: A trait that is affected by multiple genes
These traits are not discrete (yes or no) but show continuous variation.
E.g. skin color, height, etc.

Pleiotropic: when a single gene determines more than one phenotype for an organism (gene that lengthens bones lengthens legs and arms).
Gene for sickle cell affects vulnerability to malaria and sickle cell anemia.