Unit #9: Genetic and Developmental Disorders ( Flashcards
Define: Chromosome
A linear thread of nuclear DNA that becomes visible under the microscope during cell mitosis.
Define: Genes
A unit of heredity consisting of a segment of DNA nucleotides that encodes a messenger RNA capable of being translated into a protein.
Define: Alleles
One of two or more alternative forms of a gene located at the same site on the homologous chromosomes.
Define: Heterzygous
Having two different alleles for a specific gene product.
Define: Homozygous
Having two identical alleles for a specific gene product.
Define: Mutation/abberation
A heritable change in the nucleotide sequence of a chromosome; it is passed on to daughter cells when the cells divide.
Define: Genotype
The genetic constitution of an individual; often described by listing the allele types at a certain gene locus.
Define: Phenotype
The physical, biochemical, and biological composition of an individual; expressed as a recognizable trait.
Define: Congenital defect
A general term meaning a defect in form or function that is present at birth.
Define: Teratogen
An agent or factor that causes damage or physical defects in a developing embryo.
Describe: Chromosomal disorders
- Generally occur due to an abnormal number of chromosomes or alterations in the structure of one or more chromosomes.
- Errors in separation of chromosome during meiosis may result in abnormal numbers of chromosomes
- Can be tested for during pregnancy
Describe: Autosomal dominant disorders
- Dominant inheritance means an abnormal gene from one parent can cause disease. This happens even when the matching gene from the other parent is normal. The abnormal gene dominates.
- This disease can also occur as a new condition in a child when neither parent has the abnormal gene.
- A parent with an autosomal dominant condition has a 50% chance of having a child with the condition. This is true for each pregnancy.
Describe: Autosomal recessive disorders
- An autosomal recessive disorder means two copies of an abnormal gene must be present in order for the disease or trait to develop.
- Recessive inheritance means both genes in a pair must be abnormal to cause disease. People with only one defective gene in the pair are called carriers. These people are most often not affected with the condition. However, they can pass the abnormal gene to their children.
Describe: Sex-linked (X-linked) disorders
- Sex-linked diseases are passed down through families through one of the X or Y chromosomes.
- Dominant inheritance occurs when an abnormal gene from one parent causes disease even though the matching gene from the other parent is normal. The abnormal gene dominates.
- But in recessive inheritance, both matching genes must be abnormal to cause disease. If only one gene in the pair is abnormal, the disease does not occur or it is mild. Someone who has one abnormal gene (but no symptoms) is called a carrier. Carriers can pass abnormal genes to their children.
- The term “sex-linked recessive” most often refers to X-linked recessive.
- X-linked recessive diseases most often occur in males. Males have only one X chromosome. A single recessive gene on that X chromosome will cause the disease.
- The Y chromosome is the other half of the XY gene pair in the male. However, the Y chromosome doesn’t contain most of the genes of the X chromosome. Because of that, it doesn’t protect the male. Diseases such as hemophilia and Duchenne muscular dystrophy occur from a recessive gene on the X chromosome.
- females can get an X-linked recessive disorder, but this is very rare. An abnormal gene on the X chromosome from each parent would be required, since a female has two X chromosomes.
Describe: Multifactorial (Polygenic) disorders
- Polygenic traits develop in response to more than one gene.
- Multifactorial disorders are very common and result from the interaction of multiple genes and environmental influences. Disorders such as high blood pressure, cancer, and diabetes are multifactorial.
