| 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.
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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.