Genetics Terminology

Chromatin

loosely packed combination of DNA and proteins that fills the nucleus when a cell is not dividing

Chromosome

tightly coiled condensed structure of DNA that forms when chromatin packs together, usually visible only during cell division

sister chromatid

one of two identical copies of a chromosome, joined together at the centromere after DNA replication

Gamete

reproductive cell (sperm or egg) that carries half the normal number of chromosomes

Centromere

the pinched region of a chromosome where the two sister chromatids are held together

Centriole

A small cylindrical structure in animal cells that helps organize the spindle fibers during cell division

Diploid

having 2 complete sets of chromosomes (one from each parent) written as 2n

Haploid

having only one complete set of chromosomes (one from each parent) that are the same size, shape, and carry genes for the same traits

homologous

describes a matching pair of chromosomes (one from each parent) that are the same, size, shape and carry genes for the same traits

crossing over

the exchange of DNA segments between homologous chromosomes during meiosis, which increases genetic variation

cytokinesis

final stage of cell division where the cytoplasm splits, physically dividing one cell into two separate daughter cells

Metacentric

a chromosome shape where the centromere is in the middle, creating 2 arms of equal length

Acrocentric

a chromosome shape where the centromere is near one end, creating one very short arm and one long arm

telocentric

a chromosome shape where the centromere is at the very tip, so there’s essentially only one arm (no short arm)

Monohybrid cross

a genetic cross that tracks the inheritance of just one trait (one gene) between 2 parents such as crossing tall plants with short plants

selfing

when a plant fertilizes itself using its own pollen rather than receiving pollen from a different plant. this is common in self pollinating species like peas

parental Generation (P)

the original pair of individuals used to start a genetic cross-the starting point generation before any offspring are produced

First Filial Generation

the first set of offspring produced from crossing the parental generation

Second Filial Generation (F2)

the offspring produced by crossing (or selfing) individuals from the F1 generation. this generation often reveals traits that were “hidden” in the F1

Reciprocal cross

pair of crosses in which the sexes of the parents are swapped Ex: firs cross; mother has a trait A father has trait b, cross would be Mother has B father has A) used to check whether a traits inheritance depends on which parent contributes it

Phenotype

an organisms observable physical or biochemical traits- what it actually looks like or how it functions (Ex, brown eyes)

Genotype

the actual genetic makeup of an organism- the specific combination of alleles it carries for a gene (Aa) whether or not that combination us visible