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If the chromosome pair is XY, the gonads develop into testes starting in week 7. The sperm and the egg are gametes. The baby is born. Pregnancy begins once the fertilized egg implants in the uterus. The embryo contains a flat embryonic disc that now differentiates into three layers: the endoderm, the mesoderm, and the ectoderm.
In addition, the percentage of sperm that move randomly rather than in a straight line generally increases in older men. The baby was 6 weeks premature and weighed only 1.
Male gametes are made by male reproductive structures. Around years old, the decline becomes much steeper and the chances of conception significantly lower. Female monozygotic twins can also differ because of differences between them in X-chromosome inactivation. After meiosis I is complete, the egg cell is called a secondary oocyte.
Bones, muscles, skin, and connective tissues form. Plant reproductive system. Get our awesome anatomy emails! Eyes, limbs, and organs appear as the embryo develops into a fetus.
Dan Levitis and his wife, Iris, were living in Germany when they lost their first pregnancy. In another mutant, the reproductive cells' progression through meiosis was derailed. References Adelberg, Edward A.