Genotypes can be changed through selective breeding and

Genotypes can be changed through selective breeding and genetic engineering

• Work w/ Drosophila helped to shape modern genetics and knowledge of genes and chromosomes • Dros. Mel. Has advantages as genetic subject: • 1. Small and easy to keep large numbers • 2. Easy to raise • 3. Produces hundreds of offspring. • 4. Reproductive cycle of about 14 days • 5. And only 4 pairs of chromosomes These allow for many generations of flies in short time

Using fruit flies geneticists discovered Chromosomes in males and females that do not match. These are sex chromosomes – X and Y Male is XY Female XX All other chromosomes are called autosomes Fruit flies have 3 pairs autosomal chromosomes Humans have 22 pairs autosomal chromosomes

Do Punnet square to show XY x XX Y X X X X Y X Y

Note: sex is determined at fertilization when sperm – w/either x or y chromosomes, unites w/ female x Note: NOT ALL animals have male XY Birds, butterflies, some fish have male XX and female 2 different alleles

SEX LINKED TRAITS Some traits are determined by genes that are located on the X chromosome BUT NOT the Y chromosome Some ex: are hemophilia, colorblindness (usually can’t see red and green), fruit fly eye color Because males have one X and one Y If a male has a defective X chromosome he’ll express the sexlinked trait WHY? Because his one and only X chromosome is defective. If a female has only one defective X chromosome, she won’t express the sex-linked trait. For her to express the trait, she has to inherit 2 defective x chromosomes.

The SCID Homepage - About SCID a gene on the Y chromosome that is believed to determine male sexual development. Individuals with the normal female sex chromosome combination (XX) may develop as males if the TDF gene has migrated to one of the X chromosomes. Also, individuals with the normal male sex chromosome pair (XY) may develop as females if the TDF gene is missing from the Y chromosome. Mosby's Medical Dictionary, 8 th edition. © 2009, Elsevier.

A female with one defective X is called a CARRIER Although she appears normal, she can still pass the trait on to her children. HOWEVER: she has 2 bad X chromosomes, she’s out of luck. She WILL express the trait. Use a Punnet Square to show the offspring from the cross of a color-blind mother and a normal father. X X X c c Y Xc X Xc Y

Gene linkage: We have thousands of genes, as do many other organisms. Many genes are present on the same chromosome. Sometimes some genes are actually inherited together. i. e. : they DON’T OBEY Mendel's Law of Independent Assortment and if FACT are usually inherited together CROSSING OVER This is when parts of homologous chromosomes are exchanged during meiosis Because of crossing over the chromosomes of the gametes have new linkages. This is good for genetic variation

MULTIPLE GENE INHERITANCE (poly INHERITANCE OR POLYGENIC INHERITANCE) {PLEASE DO NOT confuse Multiple gene inheritance with Multiple ALLELES. } Multiple genes are when a trait is determined by more than 1 pair of alleles. Ex. : Melanin, height, length of ear of corn Ex. : Length of corn ear – using Aa and Bb as symbols for alleles, list 9 different genotypes of ear length. AABB being longest and aabb being shortest. AABB, Aa. BB, AABb, Aa. Bb, AAbb, Aabb, aa. BB, aa. Bb, aabb

GENE EXPRESSION AND ENVIRONMENT Changes in environment turns some genes on Ex. Change in temperature cause changes in expression of genes governing fur color in Himalayan rabbit. White over most of body. Black fur on ear, nose, feet, tail Produced by temp difference in certain parts of body. A gene controls production of black pigment. Black pigment on parts where temp falls below 33 degrees C.

Reptiles – incubation temp of eggs determines sex of offspring Effect of light on chlorophyll production. Most plants have ability to produce chlorophyll, they will do this only in the presence of light. W/out light, these plants produce only a light yellows pigment and appear pale and sickly until exposed to sunlight. After few days exposed to sun, chlorophyll production mechanism is enable and green color returns. Effect of temp of curled-wing in fruit flies. Researchers found that curled wing phenotype was expressed among offspring raised in “warm Environment”

Human Traits Human genes are inherited according to the same principles that Gregor Mendel discovered working with garden peas. In order to apply Mendelian genetics to humans, biologists must identify an inherited trait controlled by a single gene, which is not always easy. First, they must establish that the trait is actually inherited and not the result of environmental influences Then, they have to study how the trait is passed from one generation to the next. A pedigree chart, which shows the relationships within a family, can be used to help with this task.

In these family trees, squares symbolize males and circles represent females. A horizontal line connecting a male and female (--) indicates a mating, with offspring listed below in their order of birth, from left to right. Shaded symbols stand for individuals with the trait being traced.

Do a Punnet Square to determine the offspring of this couple & fill in the Pedigree chart.

• • • When Things Go Wrong Cells can make mistakes in copying their DNA These mistakes are called mutations Mutations are changes in the genetic material Mutagenic agents - factors in the environment that cause mutations; for example, radiation from sources such as cosmic rays, radon, X-rays, ultraviolet & radioactive or chemical such as benzene & formaldehyde Mutations that produce changes in a single gene are gene mutations Changes in whole chromosomes are chromosomal mutations

Gene Mutations I. Point Mutations ØMutations that affect one nucleotide are called point mutations because they occur at a single point in the DNA sequence 1) Substitutions üsubstitute one nucleotide for another üchange one of the amino acids in a protein

2) Frameshift Mutations v. Insertions or deletions üShift the “reading frame” of the genetic code. üMay change every amino acid that follow the point of mutation altering the protein so it is unable to perform its normal function

Chromosomal Mutations • Involve changes in the number or structure of chromosomes. • 4 types – Deletions – Duplications/Additions – Inversions – Translocations

1. Deletions Involve loss of all or part of a chromosome 2. Duplications/Additions Produce extra copies of parts of a chromosome Fragile X syndrome: Fragile X-3 Video, NCBDDD, CDC 3. Inversions Reverse direction of parts of chromosomes 4. Translocations When part of one chromosome breaks off and attaches to another

5. Non Disjunction - during meiosis, a pair of chromosomes do not separate & a gamete now has one more chromosome while the other has one less. i. e. : gametes that contain more (or less) than the monoploid (n) chromosome number

In humans, condition known as DOWN’S SYNDROME may be caused by nondisjunction of chromosome number 21 in ovum Turner’s syndrome – only has 1 sex chromosome Short statue, low hairline, Small finger nails, Fold of skin (around neck), constriction of aorta, poor breast development, Rudimentary ovaries Turner syndrome occurs in about 1 out of 2, 000 live births Klinefelter’s syndrome – has 2 “X” chromosomes and 1 “Y” chromosome

Significance of Mutations • Most mutations are neutral – have little or no effect on the expression of genes or function of proteins • Harmful mutations – producing defective proteins – disrupt normal biological activities • Source of genetic variability in a species • Cause genetic disorders • Associated with many types of cancer

Human Genetic Diseases: [recessive diseases] A. Sex-Linked Disorders More common in males than females. Because the X chromosomes carries many more genes than the Y chromosome – which has very few. When a gene is carried on the X chromosome of a male, there is no allele (corresponding gene) on the Y chromosome. So, a gene on the X chromosome of the male will ALWAYS be expressed, whether it is dominant or recessive. Many unfavorable sex-linked traits are recessive and therefore rare. When one of these recessive genes is present on a female’s X chromosome, she must carry the recessive allele on BOTH of her X chromosomes to express the trait. If it is present on only one, she is carrier. Although she will not show the trait, she can pass the allele on to offspring.

Hemophilia 1. Blood is unable to clot because it lacks a certain protein that doesn't make blood clot. 2. Duchenne Muscular Dystrophy One of nine types of muscular dystrophy, a group of genetic, degenerative diseases primarily affecting voluntary muscles. X-linked recessive. DMD primarily affects boys, who inherit the disease through their mothers. Women can be carriers of DMD but usually exhibit no symptoms. Cause - An absence of dystrophin, a protein that helps keep muscle cells intact. Onset generally before the age of 6, confinement to a wheelchair by 12 and death by 20. Symptoms include: Generalized weakness and muscle wasting first affecting the muscles of the hips, pelvic area, thighs and shoulders. Calves are often enlarged.

Do a Punnett Square to solve the following: Use the following key: XD= Normal Xd = recessive gene for MD What are the chances that a woman that carries the gene for Duchenne’s MD will have children with the disorder? Her husband is phenotypically normal. XDY x XDXd

XD Y XD XD Y Xd XD Xd Xd Y Question for thought: You are the genetic counselor for this couple. What advice would you give them?

B. Autosomal Genetic Disorders- [defective alleles on chromosomes] 1. Sickle Cell Anemia- RBC are sickle shaped which disables the blood cell to carry oxygen; in the hemoglobin molecule 1 polypeptide chain is 300 amino acids, at one point GAA which places glutamic acid, but in this disease GUA is present & places valine instead 2. Phenylketonuria (PKU)- an enzyme is missing for the normal breakdown of an phenylalanine (amino acid). Mental retardation 3. Tay-Sachs Disease - affects descendants of Eastern Europe, missing an enzyme for the breakdown of lipids & results in death

4. Cystic Fibrosis- caused by a recessive allele on chromosome 7 which cause glands to produce a lot of mucus & clog the lungs. Children with this disease also have serious digestive problems. There is no cure for this disease, only treatment. With proper treatment, people can live to early adulthood. 5. Huntington's Disease- caused by a dominant allele. Everyone with this allele (you only need) will have the disease. Any child born to a parent with Huntington’s has a 50% chance of inheriting the allele. This is a fatal disease but does not generally appear until a a person is over 30. The disease causes a progressive breakdown of the brain cells, leading to death.

Detecting Genetic Disorders A. Amniocentesis - removal of amniotic fluid from a pregnant female. The chromosomes of the fetus can be examined by a process of karyotyping and the genetic material can be studied for genetic problems. Can also determine sex of the fetus. B. Chorionic villus sampling (CVS) – related to amniocentesis – a small sample of cells from the placenta is aspirated out with a long syringe. Can be performed earlier than amniocentesis

DNA ANALYSIS C. Detection of sickle-cell can be done Southern blotting - a type of electrophoresis. . D. Using PCR – used in diagnosis of diseases in which a specific mutational site is in question.

How can a 12 year old sheep have an identical twin that is only 4 years old? ? ? This animal is part goat and part sheep. It was created by mixing together cells from separate embryos and then implanting the mixed embryo into a surrogate mother.

Selective Breeding • There are well over 300 different breeds of dogs. Where did all the differences come from? • Selective Breeding – Allowing only those dogs with desirable traits to breed for the next generation • Inbreeding is the continued breeding of individuals with similar characteristics –helps to ensure that the characteristics that make each breed unique will be preserved –Risks - the members of a breed are genetically similar –chance that a cross between two individuals will bring together two recessive alleles for a genetic defect –blindness and joint deformities in German shepherds and golden retrievers, have resulted from excessive inbreeding.

Increasing Variation • Breeders can increase the genetic variation in a population by inducing mutations, which are the ultimate source of genetic variability • Polyploidy üusually fatal in animals üplants are much better at tolerating extra sets of chromosomes ümay instantly produce new species of plants that are often larger and stronger than their diploid relatives ücrop plants have been produced in this way, including bananas and many varieties of citrus fruits

The Tools of Molecular Biology Genetic engineering making changes in the DNA code of a living organism DNA Extraction cells are opened and the DNA is separated from the other cell parts Cutting DNA molecules too large to be analyzed. Biologists cut them precisely into smaller fragments using restriction enzymes Restriction enzyme will cut a DNA sequence only if it matches the sequence precisely

The restriction enzyme Eco. RI finds the sequence CTTAAG on DNA. The enzyme cuts the molecule at each occurrence of CTTAAG. Different restriction enzymes recognize and cut different sequences of nucleotides on DNA molecules.

How can DNA fragments be separated analyzed? Gel Electrophoresis 1. a mixture of DNA fragments is placed at one end of a porous gel, and an electric voltage is applied to the gel 2. power is turned on, DNA molecules, which are negatively charged, move toward the positive end of the gel 3. The smaller the DNA fragment, the faster it moves

Making Copies technique known as polymerase chain reaction (PCR) allows biologists to make many copies of a particular gene

Genetic Engineering and Gene Splicing When DNA from two different species is joined together, it is called recombinant DNA or gene splicing. This involves breaking a DNA molecule and inserting or attaching a new gene by means of a chemical “splice”. It provides a way of producing large amounts of previously rare substance. Ex: Interferon – a protein to help fight off viruses. Growth –promoting hormones – used to increase milk production by cows or fatten farm animals. Produce human insulin

To transfer DNA, genetic engineers us a carrier of genetic material called a vector. Bacteria contain vectors called plasmids. Plasmids are small circular pieces of DNA separate from the bacterial chromosome. Ex. : to make human growth hormone (h. GH) 1. A bacterial plasmid and the human gene are removed. 2. Both DNAs are cut with the same restriction enzyme 3. The h. GH gene is inserted into the plasmid, producing recombinant DNA 4. The recombined plasmid is introduced into a bacterial cell. 5. The recombinant bacterial cell reproduces, making copies of the h. GH gene which the bacteria use to produce h. GH

Cloning A clone is a member of a population of genetically identical cells produced from a single cell. In 1997, Scottish scientist Ian Wilmut stunned biologists by announcing that he had cloned a sheep. How did he do it? The nucleus of an egg cell is removed. The cell is fused with a cell taken from another adult. The fused cell begins to divide and the embryo is then placed in the reproductive system of a foster mother, where it develops normally.

Transgenic Organisms A transgenic organism is defined as one derived from a cell whose genome has been modified by the addition of DNA from a different species. Ex. : a tomato genetically engineered to ripen more slowly thus preventing spoilage (already on the market) Genetic engineers changed and cloned the gene that codes for ripening in tomatoes. Transgenic animals can be produced by inserting DNA strands directly into an animal’s egg. Genes for animals that produce more meat or are resistant to disease may someday be inserted into the reproductive cells of livestock to create desirable characteristics in offspring.

Research has revealed how to genetically engineer bacteria that can produce a milk-stimulating hormone for cattle. If you eat cheese, chances are you have already consumed a genetically engineered food. Most cheese produce in the US has a genetically engineered component, call chymosin – this replaces a substance called rennin - from the stomach lining of slaughtered cattle - used to clot milk to make cheese.

Cures Found in DNA Codes Gene therapy – changing the genes that cause a genetic disorder. A form of gene therapy designed to control the symptoms of cystic fibrosis has been attempted (has not produced a lasting cure). Healthy genes that have recombined with certain viruses or carrier cells can be delivered to lung cells via a nasal spray. The healthy genes can then replace the malfunctioning genes, correcting the genetic defect.

Viruses are often used because of their ability to enter a cell’s DNA. The virus is modified so that they cannot cause disease. A DNA fragment containing a replacement gene is spliced to viral DNA. A patient is then infected with the modified virus carrying the gene into cells to correct genetic defects. Ex. : using gene therapy to deliver the gene for normal hemoglobin into a person’s bone marrow.

The Human Genome Project is an attempt to sequence all human DNA. Officially began in 1990. Goals were: • identify all the approximately 20, 000 -25, 000 genes in human DNA, • determine the sequences of the 3 billion chemical base pairs that make up human DNA, • store this information in databases, • improve tools for data analysis, • transfer related technologies to the private sector, and • address the ethical, legal, and social issues (ELSI) that may arise from the project.

What's a genome? • A genome is all the DNA in an organism, including its genes What are some practical benefits to learning about DNA? Knowledge about the effects of DNA variations among individuals can lead to new ways to diagnose, treat, and someday prevent the thousands of disorders that affect us and learning about nonhuman organisms' DNA can lead to an understanding that can be applied toward solving challenges in health care, agriculture, energy production, environmental remediation, and carbon sequestration.