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Genetics is the science that studies of inheritance
Inheritance is the passage of hereditary traits from one generation to the next
Genes are elements of DNA located on chromosomes that code for the production of proteins. The gene is the basic physical unit of inheritance. Genes are passed from parents to offspring and contain the information needed to specify traits. Genes are arranged, one after another, on structures called chromosomes. A chromosome contains a single, long DNA molecule, only a portion of which corresponds to a single gene. Humans have approximately 23,000 genes arranged on their chromosomes
The two chromosomes that make up each pair are called homologous chromosomes or homologs; they contain similar genes arranged in the same (or almost at the same ) order. A pair of chromosomes, one inherited from each parent, that have corresponding gene sequences and that pair during meiosis. Diploid organisms possess two copies of each gene.
Alternative forms of a gene that code for the same trait and are at the same location on gomologous chromosomes are called alleles.
If the alleles are the identical – they are homozygous
If the alleles are different – they are heterozygous
A dominant allele is an allele that is fully phenotypically expressed in a heterozygote. (example; P)
The allele whose presence is completely masked (p) is said to be a recessive allele.
Genotype is genetic makeup
Phenotype. What you look like (outward expression of your genes).
Codominance is a pattern of inheritance in which two different alleles of a gene are equally expressed in a heterozygote and no blending of the characteristic occurs.
In icomplete dominance, neither member of apair of alleles dominant ovet the other, and the heterozygote has a phetotype intermediate between the homozygous dominant and the homozygous recessive phenotypes.
Most inhetited traits are not controlled by one gene, but instead by the combined effects of two or more genes, a situation reffered to as polygenic inheritance
Complex inheritance – combined effects of many genes and environmental factors
Dominant genetic disorder
A person with a dominant genetic disorder has a 50% chance of passing it on to any given offspring.
The Marfan syndrome is a connective tissue disorder (autosomal Dominant Disorder). Connective tissue provides substance and support to tendons, ligaments, blood vessel walls, cartilage, heart valves and many other structures. In the Marfan syndrome, the chemical makeup of the connective tissue isn't normal. As a result, many of these structures aren't as stiff as they should be.e Marfan syndrome is a connective tissue disorder. Connective tissue provides substance and support to tendons, ligaments, blood vessel walls, cartilage, heart valves and many other structures. In the Marfan syndrome, the chemical makeup of the connective tissue isn't normal. As a result, many of these structures aren't as stiff as they should be. Mutations in the FBN1 gene cause Marfan syndrome. The FBN1 gene provides instructions for making a protein called fibrillin-1. Fibrillin-1 binds to itself and other proteins and molecules to form threadlike filaments called microfibrils. Microfibrils become part of the fibers that provide strength and flexibility to connective tissue. Marfan’s syndrome is a dominant genetic disorder. (M capital is syndrom)
Huntington's disease (HD)
Huntington's disease (HD) results from genetically programmed degeneration of brain cells, called neurons, in certain areas of the brain. This degeneration causes uncontrolled movements, loss of intellectual faculties, and emotional disturbance. HD is a familial disease, passed from parent to child through a mutation in the normal gene. Each child of an HD parent has a 50-50 chance of inheriting the HD gene.The normal gene has three DNA bases, composed of the sequence CAG. In people with HD, the sequence abnormally repeats itself dozens of times. Over time—and with each successive generation—the number of CAG repeats may expand further.
Error in meiosis resulting in abnormal number of chromosomes.
Aneuploidy is an abnormal number of chromosomes. Chromosomes added or missing. Is a condition in which an organism has either more or fewer chromosomes than normally exist. Generally one chromosome too many or too few. Usually caused by nondisjunction during meiosis. Also can may be an error in meiosis called translocation, location of chromosome segment is moved during crossing-over between 2 nonhomologous chromosomes.
Entire full set of chromosomes added or missing. Polyploidy is tolerated well by some species, particularly plants: cotton, soybeans, peanuts, bananas, durum wheat.
Monosomic cell missing 1 chromosome (2n-1)
Trisomic cell has additional chromosome (2n +1). Down Syndrome – trisomy 21 – 3 hromosomes on 21st chromosomes.
Most girls are born with two X chromosomes, but girls with Turner syndrome are born with only one X chromosome or they are missing part of one X chromosome
Klinefelter's syndrome is a condition that occurs in men who have an extra X chromosome in most of their cells. The syndrome can affect different stages of physical, language and social development. The most common symptom is infertility. Because they often don't make as much of the male hormone testosterone as other boys, teenagers with Klinefelter's syndrome may have less facial and body hair and may be less muscular than other boys. They may have trouble using language to express themselves. They may be shy and have trouble fitting in.
Fragile X Syndrome
Fragile X syndrome is a genetic condition involving changes in part of the X chromosome. It is the most common form of inherited mental retardation in males and a significant cause of mental retardation in females.
- Phenotype is result of environment effects on genetic makeup-more influential on polygenic traits such as height. Teratogens = cause developmental defects. Chemicals & Drugs:
- Fetal alcohol syndrome = slow growth, facial features, defective heart & CNS
- Cocaine = attention problems, hyperirritability, seizures
- Cigarette Smoking-low birth weight, cleft lip & palate, SIDS
- Irradiation or radioisotopes during first trimester-mental retardation, microcephaly
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