Exam 3: Forming a New Life: Conception,heredity,and Environment

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Dominant genes are those that are expressed when present, meaning that only one copy of the gene is needed for the trait to be displayed. Recessive genes, on the other hand, are only expressed when two copies of the gene are present. Sex-linked genes are those that are located on the sex chromosomes, such as the X or Y chromosome.

An example of a dominant gene is the gene for brown eyes. If a person inherits one copy of the gene for brown eyes from one parent and a copy of the gene for blue eyes from the other parent, they will have brown eyes because the brown eye gene is dominant.

An example of a recessive gene is the gene for red hair. If both parents carry a copy of the gene for red hair, their child may inherit two copies of the gene and have red hair, as the gene for red hair is recessive.

An example of a sex-linked gene is the gene for hemophilia, a blood clotting disorder. The gene for hemophilia is located on the X chromosome, so it is more commonly expressed in males who only have one X chromosome. Females have two X chromosomes, so they are more likely to be carriers of the gene but may not display the disorder themselves.

In terms of birth defects, an example of a defect transmitted by a dominant gene is Huntington's disease. This is a neurodegenerative disorder caused by a dominant gene mutation.

An example of a defect transmitted by a recessive gene is cystic fibrosis, a genetic disorder that affects the lungs and digestive system.

An example of a defect transmitted by a sex-linked gene is color blindness, which is more common in males due to the gene for color blindness being located on the X chromosome.