Using What We've Learned

 Humans chromosomes carry genes that control a variety of traits. Humans have 23 pairs of chromosomes. One of those pairs determines the sex of the person. They are two kinds of sex chromosomes, the X chromosome and the Y chromosome.
Like all chromosomes the sex chromosomes carry genes for many traits. Some of the genes carried on the X chromosomes are not found on the smaller Y chromosome. These are sex-linked genes.
The process of crossing plants or animals to produce offspring with certain desirable traits is called selective breeding. They use it for centuries to produce better food crops, hardier domestic animals , and prettier flowers.
Scientists have recently developed a new method of controling inherited traits in offspring. Genetic engineering is a way of changing the DNA sequence that make up a gene so that the gene will produce a particular trait.
Today 's researches have made it possible to " splice" genes. Gene-splicing is a process in which scientist can take the genes from one organism and attach to them - the genes in another organism. One example of subtances that produce a Gene-splicing is the insulin.