| MOLECULE of DNA |
| The deoxyribonucleic acid, DNA, is a long chain of nucleotides which consist of (figure 1): Deoxyribose (a pentose = sugar with 5 carbons) Phosphoric Acid Organic (nitrogenous) bases (Purines - Adenine and Guanine, or Pyrimidines -Cytosine and Thymine) DNA is a backbone of alternating sugar and phosphate atoms with one of four bases projecting from the sugar molecule. The larger of the bases -- purines -- are adenine (A) and guanine (G). Cytosine (C) and thymine (T) are the other two, called pyrimidines. DNA is a double helix and the strands are complementary, meaning that if there is a large purine on one side, there is a small pyrimidine on the other, with specific partners (adenine is always paired with thymine; guanine with cytosine). There are about 3 billion of these A, C, T, or G bases strung together to form the 46 different human chromosomes. If you unwrap all the DNA you have in all your cells ... and you have 50 to 75 trillion cells in the body ... you could reach the moon ... 6000 times! |
| INTERESTING TRIVIA: Nearly 99% of chimpanzee and human DNA is IDENTICAL. People around the world are 99.1% identical!! The small parts of a percentage make us different from each other and from chimpanzees -- what makes us human -- upright gait, ability to speak, cognitive capacity, being slightly less hairy -- the differences are VAST. |
| IMPLANTATION |
| Sites of normal and abnormal blastocyst implantation. Site of most common (normal) implantation is the posterior wall of uterus. Abnormal implantation: tubal pregnancies, ovarian, and abdominal. Implantation at the internal os generates the clinical condition placenta previa, (resulting in bleeding or placental separation during pregnancy). Note that spontaneous abortion of blastocysts is quite common and studies of blastocysts that do not implant indicate chromosomal abnormalities in many of these embryos. |
| EMBRYO |
| In the picture, ten models, approximately life-sized, represent eight weeks of embryonic development, at the end of which main organ systems, limbs and features have taken shape. The heart takes shape through stages represented by 4 to 10 of this series of models. Microvessels continue to exchange respiratory gases and nutrients between different tissues throughout embryonic and foetal development, through birth, and then life-long. The heart, ever-responsive to changing organic demands, maintains fluid communication and unity amidst the complexity of the tissues, day and night, year-in, year-out, life-long. |
| TWIN TRIVIA (though not actually trivial) . . . Twin pregnancies occur FOUR TIMES more often that twin births. The age of the mother increases the chance of having twins. Twins occur 1 in 80. Triplets occur 1 in 8000 or 9000. Quadruplets occur 1 in 700,000. |
| AUTOSOMAL DOMINANT INHERITANCE |
| AUTOSOMAL RECESSIVE INHERITANCE |
| X-LINKED RECESSIVE INHERITANCE |
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| CHROMOSOMES |
| GENES |
| Representation of the 23 paired chromosomes of the human. Chromosome: an amalgamation of a long contiguous stretch of DNA and associated proteins, that carry portions of the hereditary information of an organism. When cells are acting as they should, the chromosomes exist as superfine tangles. In meiosis or mitosis, the chromosomes appear as thin rods with a waist (centromere) in the center. All human cells (EXCEPT mature red blood cells) house all forty-six chromosomes. Which means that all cells (except for that indefatigable red blood cell) have a full complement of genes -- two of each one -- one from mommy and one from daddy. |
| Can you tell the gender of this person? Look at the 23rd pair. What is your guess? BOY?? or GIRL?? The first 22 pairs of chromosomes are called AUTOSOMES. |
| A gene isn't an active agent on its own, it is like an instruction book for making proteins which (for the most part) are the molecules that actually do the work in a cell like generating and using energy, responding to the environment, forming cellular components, and creating messaging systems that allow cells to communicate with each other. A mutation happens when there is a misspell in the gene. This can happen just by chance, or may happen as a result of radiation, carcinogens, or other chemicals that can damage DNA. A genome is all the living genes within a living thing or within a species. |
| Each and every one of the trillions of cells in the human body contains a two meter length of DNA which includes the following in each cell: 46 human chromosomes (23 pairs), 3 billion DNA subunits (the bases A, T, C, and G), 80,000 genes that code for proteins that perform all life functions. |
| During the formation of gametes, the number of chromosomes is reduced by half, and returned to the full amount when the two gametes fuse during fertilization. Meiosis produces 4 haploid cells. Mitosis produces 2 diploid cells. Diploid organisms are those with two (di) sets. Haploid organisms/cells have only one set of chromosomes, abbreviated as n. One parent cell produces four daughter cells. Meiosis differs from mitosis primarily because there are two cell divisions in meiosis, resulting in cells with a haploid number of chromosomes. |
| The process of CROSSING OVER makes the difference in MEIOSIS. This is when chromosomes next to each other break at various points along their length and they exchange segments. This process makes each individual unique. MEIOSIS produces FOUR VIABLE SPERM, but only ONE VIABLE EGG. |
| An ovum (also oocyte, ovocyte, or loosely, egg or egg cell) is a female sex cell or gamete. Ova are produced in organs called ovaries. Girls are born with all of their eggs already present in the ovaries -- about 1 to 2 million at birth. But, when a baby girl is still just a fetus (at approximately 20 weeks gestation), she is at the peak of her load of eggs -- 6 to 7 million eggs. The reduction in the number of eggs happens in a process called apoptosis. At puberty, all but about 400,000 of her eggs will have died. At most 450 of her eggs will be ovulated. Yet, by menopause, few if any eggs remain in the ovaries. The rest have vanished into the night, without a peep. The ovum is the largest cell in the body, a tenth of a millimeter across. It is the only spherical cell in the body. |
| Here is a wonderful description of sperm from Woman: An Intimate Geography by Natalie Angier: "Sperm are indeed magnificent when magnified, vigorous, slaphappy, whip-tailed tears, darting, whirling, waggling, heading nowhere and everywhere at once, living proof of our primordial flagellar past." According to the Berk text, an adult man produces about 300 million sperms a day in the testes, two glands located in the scrotum. Other sources say different things though -- what do you think will be the number reported in our movie today? Make a guess and write it down. Rewards await. One site said 12 billion per month (http://health.howstuffworks.com/adam-200126.htm). Another says 50,000 per minute or 72 million per day (http://www.vasectomy-information.com/humor/ manual.htm). And the last one that I will mention said that over a lifetime, a man will produce more than 12 trillion sperms (http://www.sex-ed101.org/articles/men/sperm_cell.html). Of the millions of sperms in ejaculated semen, only about 200 reach the egg in the woman's fallopian tube. But only one wins. |
| MEIOSIS |
| FERTILIZATION |
| The fertilized ovum is called a ZYGOTE. From two to nine weeks called an EMBRYO. After 9 weeks and until birth -- FETUS. Newborn baby -- NEONATE. |
| MITOSIS |
| A single division of a cell, which results in two daughter cells that are genetically identical to one another and to their mother cell. |
| FETUS |