26 Lecture: Prenatal Development
Lecture Transcript
Now we are going to begin the story of the lifespan. In this lesson, we explore the role of heredity and the environment in human development, prenatal development, and childbirth.
The epigenetic framework is an important tool for helping us understand the interplay between nature (or heredity) and nurture (or the environment). The terms suggest that the environment can trigger genetic potential.
Most human features are the product of several genes or are polygenic. And if you consult the causes of many diseases, you will find that they are caused by many factors or are multifactorial. Some examples include diabetes and heart disease. Some people are genetically more at risk, but lifestyle increases risk.
The basic building blocks of development are chromosomes and genes.
Chromosomes are long strands of DNA (deoxyribonucleic acid) which contains the blueprint or genetic code for our construction. Normal human cells (other than reproductive cells) have 46 chromosomes or 23 pair of chromosomes.
Genes are specific units on the strands of DNA. There are about 25,000-30,000 different human genes.
The Human Genome Project is an international research designed to explore and map the human genome. This mapping progressed rapidly and now there are questions and concerns about how to use the findings in an ethical, nondiscriminatory way. Questions about how to use this information in employment, insurance coverage, adoption, and other areas are still being considered.
Conception is the process whereby genetic material from our biological mother and father are combined to make up our own unique genetic code. This diagram of the female reproductive system shows the location of the mother’s eggs or ova in the ovaries. Each month a ripened egg is released from one of the ovaries and is drawn into the fallopian tubes. The father’s genetic material is housed in sperm and released into the vagina during ejaculation. Millions of sperm are released but only one will reach the egg, usually in the fallopian tube as it travels toward the uterus. The fertilized egg or zygote then becomes imbedded in the lining of the uterus where growth continues.
Watch the video assigned in this lesson, Life’s Greatest Miracle, for a more thorough and interesting presentation of this topic.
Gametes are reproductive cells. The sperm is the male reproductive cell. The ova are female reproductive cells. Gametes contain 23 chromosomes which is half the number of normal human cells. Sperm are produced beginning in puberty, at around age 12 in males, in a process known as spermatogenesis. Females are born with all of their eggs (about 300,000 to 400,000) but only about 400 of these eggs will ripen and mature, a process known as oogenesis, beginning at puberty. One of these ripened eggs is released each month during ovulation.
The fertilized egg is called a zygote. Fertilization typically occurs in the fallopian tube. A tubal or ectopic pre