Bio 3.3-3.4

Loci

Where alleles are located.

Allele

A variant of a gene.

Gene

Segment of DNA.

Chromosome

A structure within cells that contains DNA.

Gametes

Sex cells.

Homologous chromosomes

Two separate pairs of sister chromatids.

Tetrad

Two pairs of homologous chromosomes, split in anaphase 1.

Crossing over

Process where 2 nonsister chromatids meet at the chiasma and switch parts.

Sister chromatids

Two identical chromatids that are joined together.

Nonsister chromatids

Chromatids that meet at the chiasma in tetrads.

Meiosis I/Anaphase I

The stage where the tetrad is pulled apart into homologous chromosomes.

Meiosis II/Anaphase II

The stage where homologous chromosomes are pulled apart into sister chromatids.

Haploid

A single set of chromosomes (n).

Diploid

Two sets of chromosomes (2n).

Segregation of alleles

The separation of alleles during gamete formation.

Cell poles

End regions of the cell where chromosomes are pulled during anaphase.

Fertilization

The process in which a sperm joins with an egg.

Chiasma

The crossing over point during meiosis.

Recombinant chromosomes

Chromosomes that have undergone crossing over.

Nondisjunction

A failure to separate a tetrad or chromosome in anaphase.

Karyotype

A visual drawing of a person's set of chromosomes organized by size, shape, and number.

True Breed

An organism whose genotype is homozygous for a gene.

Homozygous

An organism with two identical alleles for a trait (e.g., RR or rr).

Heterozygous

An organism with two different alleles for a trait (e.g., Rr).

Genotype

The genetic makeup of an organism.

Phenotype

The physical trait expressed by an organism.

Probability

The chance that an event will occur.

Independent assortment

The inheritance of one trait does not affect the inheritance of another.

Law of segregation

Two alleles for a trait separate during gamete formation.

Incomplete dominance

A form of inheritance in which neither allele is completely dominant.

Codominant traits

Both dominant alleles are fully expressed in the phenotype.

Pleiotropic

A gene that influences multiple seemingly unrelated traits.

Apoptosis

Programmed cell death.

Somatic cells

Non-sex cells in an organism.

Oncogene

A gene that has the potential to cause cancer.

Mutations

Changes in the DNA sequence that can lead to cancer.

Induction

Influence of one group of cells on an adjacent group.

Morphology

The study of the form and structure of organisms.

Master control gene

A gene that regulates the expression of other genes, typically homeotic genes.