Infants normally are able to sit, stand, and walk and climb and balance their feet in a squatting position first year, within second year

within the first year, within the second year

Explanation:

Many toddlers start to sit, stand and walk by the age of 9 to 15 months of age. These are because of the changes that occur in the brain and the spinal cord. By the age of two the brain develops coordination with the muscles of the body and the infant establishes balance on the feet and hip muscles becomes strong that aids in achieving the squatting position.

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: