GENETICS AND INHERITANCE

Gregor Mendel

GENES: * a segment of DNA in a chromosome that contains the code for a particular characteristic ALLELES: * different forms of a gene which occur at the same locus on homologous chromosomes

• one allele of a gene pair can mask another and this is known as the dominant allele. the allele that is masked and not visibly expressed in the organism, is called recessive

• the genetic composition of an organism is known as the genotype • the physical appearance of an organism determined by the genotype, is known as its phenotype

• when two alleles for a particular characteristic on the homologous chromosomes are the same • when two alleles on the homologous chromosomes differ from each other, the individual is heterozygous for that particular trait

• when 2 homozygous organisms with contrasting characteristics are crossed, all the individuals of the F1 generation will display the dominant trait. • an individual that is heterozygous for a particular characteristic will have the dominant trait as the phenotype

• an organism posseses two ‘factors’ which seperate or segregate so that each gamete contains only one of these ‘factors’

COMPLETE DOMINANCE: * one allele is dominant and the other is recessive, such that the effect of the recessive allele is masked by the dominant alelle in the heterozygous condition INCOMPLETE DOMINANCE: * neither one of the two alleles of a gene is dominant over the other, resulting in an intermediate phenotype in the heterozygous condition CO-DOMINANCE: * both alleles of a gene are equally dominant whereby both alleles express themselves in the phenotype in the heterozygous condition

• there are four blood types in humans: A, B, AB or O blood groups and their genotypes: * A - I^A I^A or I^A i * B - I^B I^B or I^B i * AB - I^A I^B * O - ii

• the various ‘factors’ controlling the different characteristics are seperate entities, not influencing each other in any way, and sorting themselves out independantly during gamete formation

• the gonosomes not only control gender, but also carry sex-linked genes • sex-linked disorders occur more often in males than in females as males only have one X chromosome • if an abnormal allele occurs on the X-chromosome of the male, that characteristic will form part of his phenotype and he will suffer from the genetic disorder. he has no other X chromosome that may carry a normal allele to mask the abnormal allele. • however, when a female, who has two X chromosomes, carries an abnormal recessive allele on one X. chromosome, there is a good chance that she will carry a normal dominant allele on her other X chromosome. • this normal dominant allele masks the abnormal recessive allele and she will not suffer from the genetic disorder. she is known as a carrier. • in females, a characteristic caused by a recessive allele will only be expressed in the phenotype if both X chromosomes carry the recessive gene

• X^H X^H - normal female • X^H X^h - normal female • X^h X^h - haemophiliac female • X^H Y - normal male • X^h Y - haemophiliac male

• a pedigree traces the inheritance of characteristics over many generations

COMPLETE DOMINANCE: 1. a letter is usually chosen according to the dominant allele 2. the uppercase form of the letter will represent the dominant allele 3. the lowercase form of the letter will represent the recessive allele INCOMPLETE DOMINANCE: 1. no allele is dominant over the other. 2. two letters are chosen, one for each allele 3. third phenotype, as a result, is a combination of the two alleles CO-DOMINANCE: 1. two letters are chosen, one for each allele 2. offsprings will have a phenotype that will have equal distributions of the alleles

mutation: * any change in the genotype of an organism gene mutation: * occurs as a result of a change in the nucleotide sequence in the DNA molecule

• can cause genetic disorders. • most disorders caused by genes on autosomes are caused by recessive genes, and are called autosomal recessive disorders. • disorder caused by dominant genes are called autosomal dominant disorders. • albinism and sickle-cell disorder are examples of autosomal recessive disorders

• can be advantageous to the organism and they are passed on from parent to offspring. • these mutations also change the DNA responsible for the production of a specific protein. • if the protein made increases the organism’s chance for survival, it would be seen as a useful mutation

• occur in the non-coding DNA and have no effect on the structure or functioning of the organism

the manipulation of biological processes to satisfy human needs

harvested stem cells are placed in the damaged area and stimulated to develop into the same cell type. USES: 1. bone marrow has been used for a long time to treat cancers 2. stem cells are used to replace dead cells in the heart after a heart attack or growing skin tissue to treat burn victims or growing nerve cells to treat spinal cord injuries and parkinson’s disease SOURCES: 1. stem cells may be harvested from the placenta, embryos, bone marrow and from blood in the umbilical cord.

synthetic insulin is used to treat diabetes and is produced by genetic engineering technology: 1. the DNA with the gene coding for the production of insulin is removed from healthy human pancreatic cells 2. enzymes are used to cut the DNA into segments to isolate the specific gene 3. a plasmid is removed from a bacterial cell 4. the plasmid is cut using enzymes 5. the human insulin gene is inserted into the plasmid to form recombinant DNA 6. the recombinant DNA is placed back into the bacterial cell 7. the bacteria are placed in a fermentation tank where they reproduce rapidly to produce many copies of the insulin gene 8. the insulin is extracted from the bacteria and purified

• produce crops that are resistant to adverse conditions • increase crop yield • change the time for the ripening of fruit • increase shelf life of plant products • improve nutritional value of food • improve taste of food • developing plants with desirable characteristics • production of drugs or hormones which have fewer side-effects and is cheaper

ANIMALS: * the nucleus of an ovum is removed and replaced with the nucleus of a somatic donor cell/ diploid donor cell * the zygote is stimulated for mitosis to occur * the embryo is then placed into the uterus of an adult female PLANTS: * plants may be cloned by vegetative reproduction/asexual reproduction/tissue culture/grafting * a plant with the desired characteristics is selected * a vegetative part of the ‘parent’ plant structure is removed and placed inside a growth medium and allowed to grow

• to produce organisms with desired traits • conservation of threatened species • to create tissues/organs for transplant