Cystic fibrosis is a recessive gene disorder. the pedigree chart for a family known to have cystic fibrosis is shown below. a half shaded circle is shown connected by a straight line to an unshaded square. underneath the half shaded circle are the letters aa which represent the genotype for the first parent. underneath the second parent the letters, aa, appear representing the genotype for the other parent. below this is another row of circles and squares. this 2nd row represents the offspring. starting from the left a half shaded circle is shown connected to an unshaded square, followed by an unshaded square, and then an unshaded circle. each of the circles and squares, offspring, are connected by a horizontal straight line that connects to the parent group above. the genotype is written under each of the offspring in order from left to right; aa, aa, aa, aa. what percentage of the offspring have observable disease? 0% 25% 50% 75%

fertilization, pictured in figure 24.23a is the process in which gametes (an egg and sperm) fuse to form a zygote. the egg and sperm each contain one set of chromosomes. to ensure that the offspring has only one complete diploid set of chromosomes, only one sperm must fuse with one egg. in mammals, the egg is protected by a layer of extracellular matrix consisting mainly of glycoproteins called the zona pellucida. when a sperm binds to the zona pellucida, a series of biochemical events, called the acrosomal reactions, take place. in placental mammals, the acrosome contains digestive enzymes that initiate the degradation of the glycoprotein matrix protecting the egg and allowing the sperm plasma membrane to fuse with the egg plasma membrane, as illustrated in figure 24.23b. the fusion of these two membranes creates an opening through which the sperm nucleus is transferred into the ovum. the nuclear membranes of the egg and sperm break down and the two haploid genomes condense to form a diploid genome.

explanation:

the answer is d (apex) good luck : ))