Genetic Notes

History--

1. Gregor Mendel’s experiments with pea plants laid the foundations for the science of genetics.

2. Rosalind Franklin created images of DNA molecules through X-ray diffraction which suggested that DNA has a spiral shape.

3. Francis Crick and James Watson developed the double-helix model of the structure

   of DNA (deoxyribonucleic acid).  The DNA molecule resembles a twisted ladder and the DNA sequence forms a code. 

Genes and Heredity---

1.      Trait: any characteristic of an organism such as body shape or what it eats

·        All traits are inherited.  Hereditary material is passed from parent to offspring during reproduction.

·        Heredity is the passing of traits from one generation to another during reproduction.

·        Reproduction is the process by which organisms make more organisms of the same kind.

2.      DNA determines what traits are passed from one generation to the next—blueprint of a whole organism

·        DNA (deoxyribonucleic acid) is a large molecule found in all living things.

·        Before a cell divides, it makes a copy of its DNA. This ensures that both new cells have all the genetic information they need.

·        A molecule of DNA can be very long. To fit inside the nucleus, the DNA wraps around proteins and coils tightly. These tightly coiled structures that contain the genetic information are called chromosomes. Each chromosome carries information for many traits.

·        A genome is the complete sequence of an organism’s DNA.

3.  Gene: small section of DNA on a chromosome that carries information about a trait

·        Hundreds of genes are located on each chromosome

·        Many genes are located together on the same chromosome

·        Each gene of a gene pair is called an allele (different forms of a gene).

·        The gene combinations that might result from a genetic cross can be determined by drawing a Punnett square.

4.      Phenotype: the physical characteristics of an organism or what is expressed or shows (tall, short, color)

5.      Genotype:  all the genes that are passed on to an offspring or the genetic makeup of an organism—the letters on the Punnett square (tt, Tt, TT)

·        The genotype of an organism determines its phenotype.

6.      Dominance: means that one allele covers over or masks another allele of that trait (it will be visible or seen)

·        A dominant allele is expressed in the phenotype of an organism. If the organism has that allele, it will show that trait.

7.      Recessive alleles are seen only when a trait is recessive pure (two recessive traits---tt)

·        If an offspring has one dominant allele and one recessive allele for a trait, the recessive trait is not expressed.

8. A purebred organism is one that has two matching alleles for a trait (example: TT or tt) 

·        Homozygous: organisms that have two identical alleles for a particular trait (BB or bb)

9.  Hybrids: organisms that inherit two different alleles for a trait (Tt)

·         Heterozygous: organisms that have two different alleles for a particular trait (Bb)

10.  A Punnett square is a tool used to predict the possible genes and traits of offspring, based on the genes of their parents. (monohybrids and dihybrids)

11.  Incomplete Dominance: heterozygous alleles are both expressed, resulting in a combined phenotype.  

·        For example, in cross-pollination experiments between red and white snapdragon plants the resulting offspring are pink.

12. A pedigree is a genetic representation of a family tree that diagrams the inheritance of a trait or disease though several generations.

·        To help with record keeping, generations were labeled and numbered. The parental generation is denoted as the P1 generation. The offspring of the P1 generation are the F1 generation (first filial). The self-fertilizing F1 generation produced the F2 generation (second filial).

Biotechnology---

1. Biotechnology is the manipulation of living things to make useful products. The use of biotechnology causes changes in organisms.

2.  Selective breeding (artificial selection) is the intentional mating of organisms to produce offspring with specific traits.

·        breeding of animals or plants having desirable characteristics

·        Selective breeding in domesticated animals is the process of developing a cultivated breed over time.

·        weeding-out of undesired characteristics and the fixation of desired traits

·        crosses two different varieties of vegetable but has traits of both parents

12.  Genetic engineering changes the genetic material of a living organism.

·        Used to make medicines and treat disease

·        Used to improve crops and to produce organisms in scientific research

·        Gene splicing is one form of genetic engineering. In gene splicing, a gene from one organism is inserted into the DNA of another organism. For example, scientists have spliced the human gene for making insulin into the DNA of bacteria. This causes the bacteria to make human insulin. Insulin is a hormone that controls sugar levels in blood. Some people with diabetes cannot make enough insulin so they need to take insulin that is made by drug companies.

·        Gene splicing---strands of DNA are transferred from the cells on one species into the cells of another species; new traits can be introduced into embryonic cells; this is useful in medicine; inherited disorders by be prevented

·        For most gene splicing, scientists transfer DNA from a complex organism to a simpler one (single-celled organism---a living thing made up of only one cell).

·         disease resistance---used to make corn that is resistant to some herbicides (product that kills weeds)

·        Placing additional gene segments into cells of a vegetable to make it better tasting and last longer

·        Gene therapy involves replacing the nonworking cells with cells that have been genetically altered. Changing one gene may negatively affect other genes.

Benefits of Biotechnology---

1.  make crops that are resistant to disease, herbicides, and frost

·        Using bacterium that infects broadleaf plants such as soybean, tobacco, and tomato

·        Bacteria can be programmed to carry useful genes into the plants

2.  altered crops to make them taste better or be more nutritious

3.  The Stoneville Pedigreed Seed Company of Stoneville, Mississippi, has been using biotechnology to improve cotton for many years. The company was the first in the world to make and sell genetically altered cotton plants.

4.  Scientists have developed single-celled organisms with industrial uses. Bacteria have been developed to help clean oil spills.

Risks of Biotechnology---

1. The entire human genome has been mapped. This may lead to the treatment or cures for some diseases. Some people worry about how information about an individual’s genes could be used. For example, an insurance company might refuse to cover a person who carries a gene for a specific disease.

2.  Genes bred into some crop plants may also cross over into wild populations.

3. Genetically engineered food plants must be tested for safety. These foods could cause allergic reactions.

4. Genetically engineered crops may be too successful.

·        If one kind of rice is more nourishing than any other, all the farmers in an area might plant that kind of rice. In the short term, everyone would benefit from the modified rice. However, the new rice might be vulnerable to disease or it might not produce a crop in a particularly wet or hot weather. If people have planted only one kind of rice, they could lose the entire crop. If farmers grow many different breeds of rice, they will not lose the whole harvest.

5. Genes spliced into bacteria may cause a new disease that could not be treated with available drugs.

6.  Some people worry about harmful new organisms being made and escaping into the environment.

Genetic Disorders

An autosome or autosomal is a chromosome that is not a sex chromosome – that is to say there are an equal number of copies of the chromosome in males and females. For example, in humans, there are twenty-two pairs of autosomes and in addition there are X and Y chromosomes which are sex chromosomes.