[ 215 ] Life Science GED ® TEST SCIENCE FLASH REVIEW • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • In birds, males have a matched pair of sex chromosomes (WW), while females have an unmatched pair (WZ). In this case, do the male’s or the female’s chromosomes determine the sex of the bird offspring? Twins occur when either a fertilized cell splits or when two different egg cells are fertilized by two different sperm cells. If the twins are a boy and a girl, which of these happened? Genetic mutations are usually harmful or do not directly affect the organism, but there are sometimes beneficial mutations. Here are some mutations. Is each of the following harmful or beneficial? • white fur on polar bears • cystic fibrosis • lactose tolerance in humans • antibiotic resistance in bacteria • sickle cell anemia • cancer