NSES Content Standard C  
Life Science: The molecular basis of heredity 
Grades 9-12, page 185 

Most of the cells in a human contain two copies of each of 22 different chromosomes. In addition, there is a pair of chromosomes that determines sex: a female contains two X chromosomes and a male contains one X and one Y chromosome. Transmission of genetic information to offspring occurs through egg and sperm cells that contain only one representative from each chromosome pair. An egg and a sperm unite to form a new individual. The fact that the human body is formed from cells that contain two copies of each chromosome--and therefore two copies of each gene--explains many features of human heredity, such as how variations that are hidden in one generation can be expressed in the next. 
 

 
Benchmark 5B The Living Environment: Heredity
Grades 6-8, page 108
In some kinds of organisms, all the genes come from a single parent, whereas in organisms that have sexes, typically half of the genes come from each parent.

Benchmark 5B The Living Environment: Heredity
Grades 6-8, page 108
In sexual reproduction, a single specialized cell from a female merges with a specialized cell from a male. As the fertilized egg, carrying genetic information from each parent, multiplies to form the complete organism with about a trillion cells, the same genetic information is copied in each cell.

Benchmark 5B The Living Environment: Heredity
Grades 9-12, page 108
The sorting and recombination of genes in sexual reproduction results in a great variety of possible gene combinations from the offspring of any two parents.