Study Guide Chapter 13: Genetic Engineering

Study Guide for Genetic Engineering test

Selective Breeding Selective breeding has been used by humans for thousands of years to increase the incidence of desirable traits from a variable population and produce domestic animals and crop plants. Dog breed characteristics are maintained by inbreeding between dogs of the same characters. Excessive inbreeding also increases the chance of double-recessive genetic defects in a breed.

1) How do humans selectively breed?

Manipulating DNA Scientists use restriction enzymes such as EcoRI (also called “DNA scissors”) to cut DNA into smaller pieces that usually have “sticky ends” at specific base sequences. The sticky ends are ready to hydrogen-bond with a complementary set of bases at the end of another single chain.

2) What are restriction enzymes?

Gel electrophoresis uses electricity to separate DNA segments by length (and charge). Restriction enzymes are used to cut the DNA pieces before gel electrophoresis. Gel electrophoresis produces a DNA fingerprint of bands by base size. Bases are ATCG. DNA fingerprinting uses gel electrophoresis to identify DNA samples. The samples are cut with restriction enzymes, a gel is run, and the bands of the gel are compared with known DNA. Different DNA strands produce a unique pattern of bands.

3) Why is DNA fingerprinting used to catch criminals? Explain.

Cell Transformation Cell transformation occurs when a cell’s DNA is changed by inserting a gene from another species using genetic engineering. These new organisms are called transgenic organisms. Cell transformation only works in a small % of cells. Genes may be inserted in the wrong place, producing unexpected proteins (possible allergens), and weird offspring.

To transform a bacterium: Step 1 A restriction enzyme is used to cut a gene such as human insulin out of a DNA strand. The gene has sticky ends. Step 2 A bacterial plasmid is taken out of its cell and the circle is cut open using a restriction enzyme. The cut plasmid has sticky ends. Step 3 The gene and a genetic marker gene are inserted into the plasmid, sticking to the ends where the bases pair up exactly. DNA from two completely different organisms is called recombinant DNA. Step 4 The plasmid is put back into the bacterium. In one sample, a small percentage of bacteria are transformed. The rest do not change. Therefore the genetic marker gene is used to identify the transformed bacteria. Step 5 The transformed bacterium can then be “farmed” to produce very large quantities of the protein, such as human insulin, coded for by the gene.

4) Why are restriction enzymes needs to make transgenic organisms?

Applications of Genetic Engineering: Biotechnology An organism that grows from recombinant DNA taken from different species is called a transgenic organism.

Transgenic animals include “knockout” organisms. A knockout mouse has genes for a specific trait turned off (knocked out) so we can study how that particular gene works. Transgenic animals can help solve human genetic problems.

Transgenic plants are also called GM crops (GM for genetically modified). 25% US corn is GM corn. Inserted genes may include a gene for resistance to weed killer, or a gene that produces insecticide. The goal is usually to increase the food supply. Golden rice has a gene to produce vitamin A to reduce vitamin deficiency and childhood blindness in poor countries. A clone is a member of a population of genetically identical cells and comes from a single body cell. Clones of multicellular organisms include sheep (Dolly was the first mammal clone). Dolly developed from a single body cell. The donor nucleus of this cell was put into an egg cell without a nucleus, and grew.

5) How did scientists make Dolly the sheep?

Blood Typing : There are four basic blood types in humans: A, B, AB, and O. Type A and B are dominant alleles. O (ii) is the recessive allele. Type O is the universal donor blood type. They can give their blood to anyone without the immune system attacking the blood (there are no antigens on the blood cell). Type AB is the universal recipient. They can receive blood from anyone as there body can recognize all the antigens from different blood types.

6) What are the possible blood type combination of a mom who has Type AB blood and a father with type AB blood? Show with a Punnett square.

Sex Linked Traits: If a gene is found only on the X chromosome and not the Y chromosome, it is said to be a sex-linked trait. Usually such genes are found on the X chromosome. The Y chromosome is thus missing such genes. The result is that females will have two copies of the sex-linked gene while males will only have one copy of this gene. If the gene is recessive, then males only need one such recessive gene to have a sex-linked trait rather than the customary two recessive genes for traits that are not sex-linked. This is why males exhibit some traits more frequently than females. Common sex linked traits are red green colorblindness, male pattern baldness, and hemophilia.

7) Why are boys more likely to get sex-linked traits?

8) A woman who is colorblind marries a man who has normal vision. What percent of their children will be colorblind? Show with a Punnett Square.