|The deoxyribonucleic acid, DNA, is a long chain of nucleotides which consist of :
Deoxyribose (a pentose = sugar with 5 carbons)
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 ...
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.
|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.
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.
|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.
|AUTOSOMAL DOMINANT INHERITANCE
Autosomal means that the error occurs on an autosome (chromosomes 1 -- 22). The disorder is inherited
as picture in the illustration. A person needs to inherit just one copy of the dominant trait to have the
disorder. One of the parents has the disorder. Examples of Autosomal dominant disorders are
Huntington's Disease and Neurofibromatosis. Remember that the inheritance is based on the genetic
make-up of the parents, and the chance of inheriting the disorder varies.
|AUTOSOMAL RECESSIVE INHERITANCE
Autosomal means that the error occurs on an autosome (chromosomes 1 -- 22). The disorder is inherited
as picture in the illustration. Depending on the mode of inheritance, the chances of having an actual
autosomal recessive disorder is relatively low. If a person is affected with an autosomal recessive
disorder, s/he must inherit a defective gene from both parents. Examples of autosomal recessive
disorders are cystic fibrosis, phenylketonuria, Sickle Cell anemia, Tay-Sachs disease, albinism, and
galactosemia. Remember that the inheritance is based on the genetic make-up of the parents, and the
chance of inheriting the disorder varies.
|X-LINKED RECESSIVE INHERITANCE
The recessive gene is carried on the X chromosome. Sons of a mother who is a carrier of an X-linked
recessive trait have a 50% chance of inheriting the trait, and then will have the disorder. Daughters have
a 50% chance of inheriting the trait and being a carrier.
Examples of X-linked recessive disorders are color blindness, hemophilia, Fragile X syndrome, and
Duchenne muscular dystrophy.
|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, ova, sperm) 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 (except for mature red blood cells, sperms, and ova)
contains a two meter length of DNA which includes the following: 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
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 reach ovulation. 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
Another says 50,000 per minute or 72 million per day
And the last one that I will mention said that over a lifetime, a man will produce more than 12 trillion sperms
Of the millions of sperms in ejaculated semen, only about 200 reach the egg in the woman's fallopian
tube. But only one wins.
|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.
These pictures show 1. the egg surrounded by sperms hopeful of success; 2, a single sperm next
to the egg, making an impression; 3.I think that this is just a drawing of the magnificent egg!;
4. Some spermies.
|A single division of a cell, which results in two daughter cells that are genetically identical to one another
and to their mother cell. Here is an interactive animation about mitosis that explains the entire process and
is VERY COOL!! Go there. You will love it! And plus, I can't explain it as well, because I really don't
understand it nearly as well. It is an absolutely amazing website, and there are interactive animations about
other bodily stuff there, too.
Also note the picture below. Amazing, isn't it??
|The above inheritance pictures from
Raising Deaf Kids
The dominant gene is carried on the X chromosome. It is less common than
X-linked recessive. They do not necessarily affect males more than females,
and the inheritance varies depending on whether the father or mother has the
dominant X. All daughters of an affected father will also be affected, but none
of his sons will (dad is Xy, so all daughters get the X and all sons get the y.) No
matter what, if a daughter inherits the mutated gene, she will have the disorder.
Males that inherit the mutated gene will have a double whammy since the y
chromosome is so little. Often an X-linked dominant disorder is fatal in boys.
Examples of X-linked dominant disorders are Rett Syndrome, Aicardi
syndrome, and Coffin-Lowry syndrome.