Contents
Genes and Chromosomes
A sperm (male reproductive cell) pushes through the membrane of the ovum (female reproductive cell) and becoming one cell, a zygote. These gametes (sex cells- Sperm T Ovum) contain huge amounts of genetic information.
Over 2 billion chemically coded messages—is sufficient to begin creating a whole person. The blueprints for creating a person are stored and communicated in our genes, the basic units of genetic information. The roughly 25,000 human genes are the biological equivalent of “software” that programs the future development of all parts of the body’s “hardware.”
All genes are composed of specific sequences of DNA (deoxyribonucleic acid) molecules. The genes are arranged in specific locations and in a specific order along 46 chromosomes, rod-shaped portions of DNA that are organized in 23 pairs.
25,000 genes= 46 Chromosomes= 23 Chromosome Pairs= One Human Cell
Important terminology
Zygote-the new cell formed by the process of fertilization.
Genes– the basic units of genetic information.
DNA (deoxyribonucleic acid) molecules the substance that genes are composed of that determines the nature of every cell in the body & how it will function.
Chromosomes– rod-shaped portions of DNA that are organized in 23 pairs.
Genetic Principles
- What determined the color of your hair? Why are you tall or short? What made you susceptible to hay fever? And why do you have so many moles?
- Austrian monk, Gregor Mendel, 1800s. In a series of experiments, cross-pollinated pea plants that always produced yellow seeds with pea plants that always produced green seeds.
- Dominant trait the one trait that is expressed when two competing traits are present.
- Recessive trait a trait within an organism that is present, but is not expressed.
- The genetic information is known as the organism’s genotype.
- Did you find that one child shows combined features of both parents, another resembles just one parent, whereas a third is not like either parent?
- Genotype the underlying combination of genetic material present (but not outwardly visible) in an organism.
- Phenotype an observable trait; the trait that is actually seen.
Chromosomal and Gene linked Abnormalities
Down syndrome/ mongolism –
- Disorder produced by the presence of an extra chromosome on the twenty-first pair.
- Down syndrome is the most frequent cause of mental retardation.
- It occurs in about 1 out of 700 births, although the risk is much greater in mothers who are unusually young or old (Sherman et al., 2007; Davis, 2008; Channell et al., 2014).
Fragile X syndrome
- A disorder produced by injury to a gene on the X chromosome, producing mild to moderate mental retardation.
Sickle-cell anemia.
- Around one-tenth of people of African descent carry genes that produce sickle-cell anemia, and
- 1 in 400 actually has the disease.
- A blood disorder that gets its name from the shape of the red blood cells in those who have it.
- Symptoms include poor appetite, stunted growth, a swollen stomach.
Tay-Sachs disease
- in Jews of Eastern European ancestry and in French-Canadians,
- Tay-Sachs disease usually causes death before its victims reach school age.
- There is no treatment for the disorder, which produces blindness and muscle degeneration prior to death.
Klinefelter’s syndrome.
- One male out of every 500 is born with
- the presence of an extra X chromosome. The resulting XXY complement produces underdeveloped genitals, extreme height, and enlarged breasts.
- genetic abnormalities that result from receiving the improper number of sex chromosomes.
- For instance, there are disorders produced by an extra Y chromosome (XYY), a missing second chromosome (X0, called Turner syndrome), and three X chromosomes (XXX). Such disorders are typically characterized by problems relating to sexual characteristics and by intellectual deficits (Murphy & Mazzocco, 2008; Murphy, 2009; Hong et al., 2014).