Genetic Influence in Disease (RRD #1)

gene

a segment of a DNA moelcule that is composed of an ordered sequence of necleotide bases (adenine, guanine, cytosine, thymine).

What is the main function of genes?

To code for the synthesis of proteins that form our traits and functional characteristics. These proteins can be permanent or functional in purpose.

When there is a mutation of a gene...

the protein it is responsible for often malfunctions.

A chromosome

a DNA molecule that is made up of a series of genes. We receive 23 chromosomes from each parent, so we end up with 23 pairs. 22 of these are autosomal, one is a sex chromasome.

Alleles

Partner genes that code for the same trait on a pair of chromosomes. They have the same location on each chormosome. Each allele in the pair of genes on the chromosome can be dominant, recessive, or both.

dominant genes

are noted in a Punnett square with an upper case letter

recessive genes

are noted in a Punnett square with a lower case letter

genotypes

The combination of partner genes (alleles) located on the chromosome that represent what was inherited from mom and dad. Examples of various combinations (randomly using the letter "g"), can be GG (homozygous dominant), gg (homozygous recessive) or Gg (heterozygous).

phenotype

How the disorder looks. The signs and symptoms of the disorder.

multifactorial genetic disorders

a combination of environmental triggers and variations /mutations of genes plus sometimes inherited tendencies.

teratogenic disorders

any influence (drugs, radiation, viruses) that can cause congenital defects. Congenital defects: abnormalities that are either detectable at birth and / or can be contributed to fetal development glitches.

chromosomal disorders / chromosomal aberrations

a type of genetic disorder that results from alterations to the development or structure of a chromosome, which in turn alters the local genes and their functionality. Ex. Down's Syndrome.

single gene disorders

These are usually due to an inherited mutated gene. They occur in recognizable patterns: autosomal recessive, autosomal dominant, and sex-linked.

autosomal recessive disorders

occurs when a mutated recessive gene on one chromosome partners up with a mutated recessive gene on the other. These partner genes (alleles) are noted with two lower case letters: gg. Example: Sickle Cell Anemia

anemia

less than normal numbers of red blood cells (RBC's). Symptoms of anemia include: shortness of breath (SOB), weakness, and fatigue because fewer RBCs means less less hemoglobin, which in turn carries O2 to the tissues.

sequela of sickle-shaped RBC's

Abnormal shape: doesn't "flow" through the circulatory system easily, becomes marked for destruction sooner by the body, clogs the microcirculation of the joints, causing ischemic pain, deformed Hgb can't carry as much oxygen.

What is a sickle cell carrier / sickle cell trait?

The individual has a heterozygus genotype for sickle cell anemia, can pass the gene on to their offspring, and may have mild s/sx of sickle cell disease.

autosomal dominant disorders

occurs when a mutated dominant gene on one chromosome partners up with a mutated dominant gene on the other. In a dominant disease, the mutated gene is the strong one, so even if it is paired with a normal allele, it will override the normal allele's coding. These partner genes (alleles) are noted with two upper case letters: PP or Pp. Example: polycystic kidney disease (PKD)

signs and symptoms of polycystic kidney disease

cysts in kidney tissue, hematuria (blood in urine), frequent kidney infections, pain at costovertebral angle and in abdomen, frequent kidney stones.

A & P of sex-linked disorders

For females, the two X's will work just like autosomal chromosomes - a gene on one X has a partner allele at the same locus on the other X. But with males, the genes on his X will have no partner on the Y gene. The most common type of sex-linked disorder are "x-linked recessive disorders"

Why do x-linked recessive disorders happen to males?

x-linked recessive disorders are caused by a recessive allele that is always located only on an x chromosome. Females are typically carriers, because theu are often protected by a normal dominant gene on their other x chromosome. Males will express the disorder because their partner gene is a Y chromosome with no partner allele. An example of an x-linked recessive disorder in males: hemophilia.

What is recombinant DNA?

New DNA that results from purposefully combining two or more sources of DNA. This has produced many useful applications to medicine: human growth hormone, exogenous inculin, factor VIII for hemophiliacs, and "clot-busting drugs" like tPA for patients who are having a heart attack or ischemic stroke.