Chapters 13 & 14 Genetic Engineering & Human Genetics

Genetic Engineering Intro: Genetic Engineering – the process of making changes in the DNA code of living organisms What are ways that humans have affected the DNA of bacteria? Plants? Animals? HUMANS????? Are these ethical issues? Why or why not?

Selective Breeding Organisms are selected for breeding based on desireable traits. These desired variations are sought out in the offspring, then bred over generations to enhance those particular traits Traits are not chosen by nature for survival of the organism, but chosen by man to ‘enjoy ’ Examples: Modern corn originated from small-grained grasses, large-fruiting plants, dog breeds, etc

Examples of Selective Breeding:

Hybrids Hybrids – offspring of crosses between parents with different traits. Used by scientists to try to get the “best” traits from each organism Hybrids can be formed between closely related species Ex: Horse 62 chromosomes x donkey 64 chromosomes = mule 63 chromosomes Many hybrids are infertile and cannot reproduce

Examples of Hybrids

Inbreeding Inbreeding – the continued breeding of individuals with similar characteristics Positives – helps maintain “breeds” of organisms Negatives – reduces the genetic variation and increases the likelihood that two recessive genes for a disease or defect can come together

Inbreeding

Polyploidy Scientists introduce chemicals that stop chromosomal separation during meiosis Result: Organisms with double or triple (or more) the number of chromosomes Common in plants, usually fatal in animals

Examples of Polyploidy: A pair of Pelargonium xhortorum (4X, 2X) flowers is on the left. A pair of P. peltatum (4X, 2X) flowers is on the right. Within each pair, the flower on the left is the tetraploid, while the flower on the right is the diploid. One of the classic "advantages" that polyploids exhibit is that they may have a larger flower size. The Pel flowers above are typical --- in each pair of flowers, the tetraploid on the left is visibly larger. –garden genetics.com

Genetic Engineering Genetic engineering – scientists make changes in the DNA of a living organism Includes: Includes cutting, copying, and pasting DNA to create transgenic bacteria, plants, and animals Recombinant DNA – DNA produced by combining DNA from different sources Examples: Human insulin made by bacteria, genetically modified foods that resist pests, goats that produce spider silk in their milk, and pGlo gene from jellyfish inserted into other organisms

A bacterial plasmid (circular piece of DNA, shown in red) has new DNA (blue) inserted, creating a recombinant plasmid

Transgenic plants and animals: Plants with gene for increased salt tolerance inserted pGlo gene inserted in bacteria and mice

Cloning Cloning – the process by which one organism’s DNA is removed from ONE cell and placed into an ennucleated (nucleus removed) egg cell from a donor This egg cell is grown in “foster” mother The offspring is genetically identical to the original organism

Cloning

Ethical Issues in Genetic Engineering: Gene therapy – using new genes injected into humans to cure diseases Stem cells – from the body or fetuses – can develop into any body cell Transgenic organisms – GM foods, creating new organisms Cloning – failure rates, humans??

Chapter 14 The Human Genome

Human Chromosomes Humans have 46 total chromosomes 23 from each parent come together to form homologous pairs 44 Autosomes 2 sex chromosomes, XX or XY If non-disjunction occurs in meiosis, humans can have less or more chromosomes

Normal Karyotype

Abnormal Karyotype

What can a karyotype reveal? Aneuploidy Trisomy – one extra chromosome: Down syndrome (47, XX, +21),, Kleinfelter’s syndrome 47, XXY, etc. Monosomy – missing one chromosome Turner’s syndrome(45, X) etc. Translocations – pieces of chromosomes moved to other chromosomes LinkLink

Pedigrees

Hemophilia pedigree

alternate hemophilia pedigree

Other factors that affect gene expression: Polygenic traits – many human traits are controlled by more than one gene How does the environment affect your phenotype (what you are physically)? “Nature vs. Nurture” Twin Studies – Are identical twins always “identical”? Separated twins? The Jim TwinsThe Jim Twins Nutrition and treatment by parents?

Genetic Diseases Scientists have identified over 4,000 diseases caused by “genetic variants” On average, individuals carry between 5 and 10 variant or disease causing genes in their genome (kidshealth.org) Why don’t we all exhibit disease symptoms then?

Human Genetic Diseases caused by recessive traits: Albinism – lack of melanin Cystic fibrosis – problems transporting chloride ions = lung, digestive problems Phenylketonuria (PKU) – metabolic disorder Tay-Sachs disease – Jewish descent, early death Individuals can be asymptomatic carriers because they have one normal gene Individuals with the disease must get one “bad” gene from each parent

Human Genetic Diseases caused by dominant traits: Achondroplasia – form of dwarfism “LPs” Huntington’s Chorea – causes mental deterioration in middle age and later. Leads to complete debilitation and death Marfan Syndrome – connective tissue disorder, tall stature Individuals only need one copy of the defective gene to cause the disease If married to a “normal” person, there is a 50% chance of passing the disease on to your children

Human Genetic Diseases that are sex-linked: Colorblindness – cannot distinguish between red and green Hemophilia – blood clotting disorder Duchenne muscular dystrophy – severe muscle weakness Defective gene is found on the X chromosome If the gene is dominant, males and females can get it equally If gene is recessive (examples on left), males get it more frequently, because females have XX, one “normal X, and one X with the defective gene