In rats, hair color is either gray (G), black (g), or white. The white color is produced due to an epistatic recessive allele of gene "a". In other words, in order for the black or gray color to show up, the rat must have at least one dominant (A) epistatic allele. Two heterozygous Gray rats are crossed. Both rats are also heterozygous for the epistatic gene.

Predict the probability that an offspring of this cross will:

a. Express the gray phenotype

b. Express the black phenotype

c. Express the white phenotype

the answer is b.) hydrogen bonds between bases.

in 1859, charles darwin set out his theory of evolution by natural selection as an explanation for adaptation and speciation. he defined natural selection as the "principle by which each slight variation [of a trait], if useful, is preserved".

interphase

the period of cell growth when the cell synthesizes new molecules and organelles. the cell is not dividing and it constitutes the majority of the time spent in the cell cycle

prophase

changes occur in the nucleus and cytoplasm. the chromatin condenses to form structures (sister chromatids) visible with a light microscope and the mitotic spindle begins to form, but the nucleus is still in tact

prometaphase

the nuclear envelope fragments and the spindle microtubules attach to the kinetochores of the sister chromatids

metaphase

all the cell's duplicated chromosomes are lined up at an imaginary plane equidistant between the poles of the mitotic spindle

anaphase

begins when sister chromatids separate from each other and ending when a complete set of daughter chromosomes arrives at each of the two poles of the cell

telophase

the daughter nuclei form at the two poles of a cell

cytokinesis

the division of a cytoplasm to form two separate daughter cells. usually occurs during telophase during mitosis. this and mitosis make up to mitotic (m) phase of the cell cycle