Genetics

1. Genetics

4. Refresh students by discussing Mendel�s major concepts of dominance and segregation (162-174). The factors that control heredity are individual units called �genes�, which are inherited from each parent (through sexual reproduction). The genes may be dominant or recessive. The two forms of each gene are segregated during the formation of reproductive cells. Genes for different traits may assort independently

5. Define the following terms associated with genetics . Trait � characteristic of an organism Gene � a heredity unit that contains a code for a sequence of amino acids in a protein chain. Allele � the alternate or contrasting forms of a gene. Dominant � the gene that is expressed whenever it is present in the cell. Recessive � the gene that is �hidden�. It is not expressed unless a homozygous condition exists for the gene. Gamete � sexual reproductive cell. Fertilization � the fusion of two gametes. Phenotype � a physical trait in an organism. Genotype � the combination of dominant and/or recessive genes present in cells. Homozygous � two identical alleles for a given trait. Heterozygous � two different alleles for a given trait.

6. Demonstrate how a Punnett square can be used to predict the results of a genetic cross (Mono/Dihybrid crosses) (170-174). Setting up the problem. Determine the traits used. Determine the dominant vs. recessive trait. Determine the letters for each trait. Express the cross and determine the gametes formed. Set up the Punnett Square. Place the 2 female gametes across the top, the 2 male gametes down the side. Determine the offspring � fill in the squares. Follow the column straight up to find gamete from female parent. Follow row across to find gamete from male parent. Sample problem � Show the cross between a homozygous blue flowered plant and a homozygous white flowered plant. Blue is dominate to white. Traits � blue flowers, white flowers Blue is dominant to white Blue � B White � b BB x bb The Punnett Square

7. Note: the dominant trait is always written first BB and bb are the parental or P1 generation. Sample problem � If Bb x bb, half will be heterozygous (Bb), half homozygous recessive (bb). Note: Phenotype ratio 2:2.

8. DIHYBRID CROSSES:� A dihybrid cross is a cross between two individuals identically heterozygous at two loci for example, AaBb/AaBb. A dihybrid cross is often used to test for dominant and recessive genes in two separate characteristics In the pea plant, two characteristics for the peas, shape and color, will be used to demonstrate an example of a dihybrid cross in a punnett square. R is the dominant gene for roundness for shape, with lower-case r to stand for the recessive wrinkled shape. Y stands for the dominant yellow pea, and lower-case y stands for the recessive green color. By using a punnett square (the gametes are RY, Ry, rY, and ry): The result in this cross is a 9:3:3:1 phenotypic ratio, as shown by the colors, where yellow represents a round yellow (both dominant genes) phenotype, green representing a round green phenotype, red representing a wrinkled yellow phenotype, and blue representing a wrinkled green phenotype (both recessive genes).

9. Differentiate between the diploid and haploid condition of a cell and identify the diploid (2n) and haploid (n) chromosome number in human cells (121&153). The number of chromosomes in a body cell of an organism is the diploid number. In human, this number is 46. Half of the diploid number is called the haploid number. In humans, this number is 23 and is found only in the gamete cells. A cell that is diploid contains both sets of homologous chromosomes (one set from each parent). Thus, haploid cells contain only a single set of chromosomes. Explain how gender is determined (122) Gender is determined by the combination of sex chromosomes inherited in the zygote. More specifically, it is the sex chromosome within the sperm that is the determining factor (it provides either an X or Y). Also, it has been discovered that the Y chromosome carries a single gene, TDF (Testis Determining Factor) that determines maleness. (Girl= XX, Boy= XY)

10. Distinguish between sex chromosomes and autosomes(122). There are 23 pairs of chromosomes in humans. Twenty-two pairs are autosomes, and one pair is the sex chromosome. The X chromosome is larger that the Y and it has extra genes on it that code form regular body traits. Explain the inheritance of sickle-cell anemia (176-180). An amino acid substitution results in the sickle shape of the red blood cells. This causes the red blood cells to have low oxygen carrying capacity, and deprive tissues of oxygen. This can be fatal. The cell shape is elongated and curved, hence the �sickle� name. This is in lieu of the biconcave disk shape of normal cells. This disease is found almost exclusively in the African-American population and affects about 1 out of every 623 A.A. infants born in the U.S. The disease exists in individuals who are homozygous; heterozygous individuals do not exhibit symptoms of the disease, but are considered carriers and have a resistance to malaria

11. Identify the causes of Down�s, Turner�s, and Klinefelter�s syndromes and identify them by their karyotypes (122-123). Nondisjunction is the failure of chromosomes to separate properly during one of the stages of meiosis. XXY produces Klinefelter�s syndrome (male appearance, underdeveloped testis, enlarged breasts, usually sterile, often mentally retarded). XO is Turner�s syndrome (female anatomically and physiologically, rudimentary ovaries, no menstruation or ovulation). YO seems to be fatal, none have been found. Other multiple sex chromosomes usually produce some abnormalities. Down�s syndrome (G trisomy, three #21 chromosomes) produces mental retardation and distinctive facial characteristics.

12. Distinguish between sex-linked and autosomal disorders, Incomplete dominance, and Codominance (171, 175-178, 180). Sex-linked diseases are inherited through one of the "sex chromosomes" -- the X or Y chromosomes. Autosomally inherited diseases are inherited through the non-sex chromosomes (autosomes), pairs 1 through 22. Dominant inheritance occurs when an abnormal gene from ONE parent is capable of causing disease even though the matching gene from the other parent is normal. The abnormal gene dominates the outcome of the gene pair. Recessive inheritance occurs when BOTH matching genes must be abnormal to produce disease. If only one gene in the pair is abnormal, the disease is not manifest or is only mildly manifest. However, the genetic predisposition to disease can be passed on to the children. Examples: (X-linked recessive),Color blindness�, �hemophilia A , Duchenne muscular dystrophy, (X-linked dominance): Retinitis pigmentosa , Rett syndrome , Vitamin D resistant rickets

13. X-linked diseases usually occur in males. Males have only one X chromosome, so a single recessive gene on that X chromosome will cause the disease. Although the Y chromosome is the other half of the XY gene pair in the male, the Y chromosome doesn't contain most of the genes of the X chromosome and therefore doesn't protect the male. This is seen in diseases such as hemophilia and Duchenne muscular dystrophy. Females can get an x-linked recessive disorder, although it would be very rare. An abnormal gene on the X chromosome from each parent would be required, since a female has 2 X chromosomes. For an autosomal dominant disorder: If one parent has an abnormal gene and the other parent a normal gene, there is a 50% chance each child will inherit the abnormal gene, and therefore the dominant trait. Examples: Achondroplasia (dwarfism), Huntington disorder, neurofibromatosis, Polydactyly, Marfan syndrome

14. For an autosomal recessive disorder: When both parents are carriers of an autosomal recessive trait, there is a 25% chance of a child inheriting abnormal genes from both parents, and therefore of developing the disease. There is a 50% chance of each child inheriting one abnormal gene (being a carrier). Examples:� Galactosemia (the inability to metabolize lactose), cystic fibrosis, phenylketonuria, xeroderma pigmentosa, Tay-Sachs disease, Sickle cell disease INCOMPLETE DOMINANCE:� A heterozygous condition in which both alleles are partially expressed, often producing an intermediate phenotype. (sometimes called partial dominance) For example, when a snap dragon with red flowers is crossed with a snap dragon with white flowers, a snap dragon with pink flowers is produced�.OR�Like in Caucasians, the child of straight haired parents and a curly haired parent will have wavy hair� Straight and curly hair are homozygous dominant traits and wavy hair is heterozygous and is intermediate between straight and curly

15. CODOMINANCE:� In codominance, neither phenotype is completely dominant. Instead, the heterozygous individual expresses both phenotypes. A common example is the ABO blood group system. The gene for blood types has three alleles: A, B, and i. i causes O type and is recessive to both A and B. The A and B alleles are codominant with each other. When a person has both A and B, they have type AB blood.

16. Interpret human pedigrees to determine the inheritance and probability of human genetic disorders (176).The parental generation is at the top of the pedigree, and the offspring are on the next line, connected by a line. Marriages are shown by a line between one of the offspring and a new circle or square, not connected above. The grandchildren will be two lines down, and traceable to their parents form direct lines.

17. Identify advances in genetic technology and the ethical responsibilities that follow. (238-242) With the increasing strides in genetic engineering comes more responsibility and ethical concerns involving the safety with this type of advancement in altering both plant and animal genetic make-up. There are many benefits and risks involved with genetically modified crops and animals, which scienctists, the public, and other agencies must work together to evaluate. In the twentienth century, advances in plant breeding started using the principles of genetics to select plants. Today, genetic engineers can change/add favorable characteristics to a plant by manipulating the plant�s genes�such as: developing bigger/tastier crops, being able to tolerate drought and different climates, heat/cold, adapting to different soils, resistant to insects, and improving the nutritional values of the crop plants, etc� Soon after the advances with crop plants, farmers started using genetic engineering to improve and modify the farm animals. Altering growth hormone amounts in the animals diet increased many things such as weight, milk production, etc� Another way gene technology is used with animals is adding in human genes to farm animals in order to get human proteins produced in their milk. The proteins are then sold for pharmaceutical purposes. These animals are called transgenic animals because they have foreign DNA in their cells.

18. Cloning is also a very controversial topic in this field. Scientists turn to cloning as a way to create herds of identical animals that can make medically useful proteins. They have successfully cloned animals since 1996, but most have not survived due to many different technical complications�because of these technical and ethical problems, efforts to clone humans are illegal in most countries. Launch of Human Genome Project (1988) First mammal cloned (sheep, in Scotland, by Ian Wilmut) (1996) Legislation to ban cloning dies in US Senate after heavy lobbying by the biotech industry. Senators are told that human cloning wouldn't be technically possible for "at least 10 years (1998) A child conceived in part to provide therapeutic tissues for an earlier-born sibling is born. Techniques of preimplantation genetic diagnosis are used to ensure that the child does not itself carry the disease. The press erroneously hails the child as the world's first "designer baby (2000)

20. US congressional hearings begin on legislation banning human cloning(2001) Scientists at Texas A & M University announce that they cloned a cat in December, the first cloning of a house pet(2002) The first complete sequence, accurate to 99.999%, of the genetic code of a single human is announced (2003) A horse is cloned(2003) Korean researchers announce that they have succeeded in cloning human embryos and extracting stem cells from them. A mouse is born with two female parents and no male parent (2004) Use of preimplantation genetic diagnosis (PGD) to provide stem cells for children suffering from non-genetic diseases.(2004)