Sex chromosomes: Chromosomes that determine biological sex in an organism, with humans typically having XX (female) or XY (male) combinations.
Recessive gene: A gene that must be present in two copies (homozygous) to express a trait unless it is located on the X chromosome in males.
Hemizygous:The condition of having only one copy of a gene or chromosome instead of the typical two; relevant for genes on the X chromosome in males