biology chapter 3 Flashcards
genetics
is the study of how traits are inherited from one generation to the next
gene
the basic unit of heredity
alleles
when a gene exists in more than one form
genotype
the genetic makeup of an individual
phenotype
the physical manifestation of the genetic makeup
dominant
expressed allele
recessive
the silent allele
homozygous
organisms that contain two copies of the same allele
heterozygous
organisms that carry two different alleles
monohybrid cross
only one trait is being studied in this particular mating
testcross
an organism with a dominant phenotype of unknown genotype (Ax) is crossed with a phenotypically recessive organism (genotype aa)
dihybrid cross
parents differ in two traits, as long as the genes are on separate chromosomes and assort independently during meiosis
crossing over
exchanges information between chromosomes and may break the linkage of certain patterns
codominance
occurs when multiple alleles exist for a given gene and more than one of them is dominant
sex linked
genes that are located on the X or Y chromosome
nondisjunction
is either the failure of homologous chromosomes to separate properly during meiosis I, or the failure of sister chromatids to separate properly during meiosis II
trisomy
three copies of that chromosome
monosomy
a single copy of that chromosome
mutagenic agents
include cosmic rays, x-rays, ultraviolet rays, and radioactivity as well as chemical compounds such as colchicine or mustard gas
colchicine
inhibits spindle formation, thereby causing polyploidy