2. A section of a chromosome and the basic unit for the transmission of heredity, consisting of a string of chemicals that are instructions for the cell to manufacture certain proteins. Click for Term
3.
4. A 23 rd chromosome pair that consists of two X-shaped chromosomes, one each from the mother and the father. XX zygotes become females. Click for Term
5.
6. The molecule that contains the chemical instructions for cells to manufacture various proteins. Click for Term
7.
8. The chromosome pair that, in humans, determines the zygote’s (and hence the person’s) sex. Click for Term
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10. One of the 46 molecules of DNA (in 23 pairs) that each cell of the human body contains and that, together, contain all the genes. Other species have more or fewer molecules. Click for Term
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12. An international effort to map the complete human genetic code. The effort was essentially completed in 2001, though analysis is ongoing. Click for Term
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14. The single cell formed from the fusing of two gametes, a sperm and an ovum. Click for Term
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16. A 23 rd chromosome pair that consists of an X-shaped chromosome from the mother and a Y-shaped chromosome from the father. XY zygotes become males. Click for Term
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18. Referring to a gene carried on the X chromosome. If a boy inherits an X-linked recessive trait from his mother, he expresses that trait because the Y from his father has no counteracting gene. Girls are more likely to be carriers of X-linked traits but are less likely to express them. Click for Term
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20. A person whose genotype includes a gene that is not expressed in the phenotype. Such an unexpressed gene occurs in half of the person’s gametes. Generally , only when such a gene is inherited from both parents does the characteristic appear in the phenotype. Click for Term
21.
22. A gene that has several alleles, each of which contributes to the final phenotype (such as skin color or height). Click for Term
23.
24. A condition in which a person has 47 chromosomes instead of the usual 46, with three rather than two chromosomes at the 21 st position. They often have distinctive characteristics, including unusual facial features, heart abnormalities, and language difficulties. Click for Term
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26. Twins who originate from one zygote that splits apart very early in development. Also called identical twins . Click for Term
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28. Referring to a trait that is influenced by many genes. Click for Term
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30. A genetic disorder in which part of the X chromosome seems to be attached to the rest of it by a very thin string of molecules. The cause is a single gene that has more than 200 repetitions of one triplet. Click for Term
31.
32. Twins who are formed when two separate ova are fertilized by two separate sperm at roughly the same time. Also, called fraternal twins . Click for Term