Chapter+Eleven


 * __ CHAPTER 11 __**** : Observable Patterns of Inheritance: GENETICS **

1. Gregor Mendel through his experimental crosses with pea plants gathered indirect evidence that diploid organisms had “pairs of genes” and that the genes retained their identity when transmitted to the next generation. He is commonly thought of as the father of modern genetics, the study of inheritence patterns. 2. There are a number of key terms used in modern genetics.  A. GENES are small sections of DNA that contain the units of genetic information related to specific traits that are passed from one generation to the next. _**ALLELES** are alternative forms Homologous Chromosomes of genes. For each inherited trait, each organism has TWO genes, one from each parent. The genes are found at the same location (locus) on homologous chromosomes. Gene Locus B. When the genes from each parent are the _**HOMOZYGOUS** for the characteristic trait. When offspring inherit a pair of //identical// alleles they represent a Three Pairs of Alleles true breeding lineage. C. When the genes from each parent are __pair of //non-identical// alleles, they are referred to as__ **HYBRIDS** _. D. An allele that masks the physical trait expressed by any allele it is paired with is called a **DOMINANT** ALLELE. It is represented by the use of a “CAPITAL” letter. The actual letter used is insignificant. E. An allele that has no noticeable effect on the organism’s physical traits, and appears to remains “hidden” when paired with another allele, is called a **RECESSIVE** __ALLELE. It is represented by the use of a “lower case” letter. The actual letter used is insignificant.__ __F. If an individual has a pair of dominant alleles (AA for example) for a specific__ __trait, they are described as being__ **HOMOZYGOUS** _ DOMINANT. G. If an individual has a pair of recessive alleles (aa for example) for a specific trait, they are described as being **HOMOZYGOUS**___ RECESSIVE.__
 * SAME**, the organism is said to be Pair of Alleles
 * DIFFERENT** from each other, the organism is said to be
 * _____HETEROZYGOUS** __for the characteristic trait. When offspring inherit a__

__H. If an individual has a pair of non-identical alleles, one dominant and one recessive (Aa for example) for a specific trait being studied, they are described as being__ **HETEROZYGOUS** . In this case, the dominant allele will “mask” the physical traits expressed by the recessive allele. I. An organisms physical appearance may not always reveal its genetic composition. homozygous dominant (AA) and heterozygous (Aa) organisms will both appear as having a “dominant” trait. Geneticists therefore distinguish between the “appearance” of a physical trait and the “genetic make-up” that caused the trait to be present. 1.**GENOTYPE** refers to the actual genetic make-up, the particular alleles present. Examples: AA, Aa or aA, and aa. 2.**PHENOTYPE** refers to the observable traits or outward physical appearance of an organism. Example: A (dominant) or a (recessive). J. When tracking the inheritance of traits through several generations, geneticists use the following terminology: 1. **P**_ generation (parents) 2. **F1**_ generation (sons and daughters) 3. **F2**_ generation (grandsons and granddaughters)

3. Gregor Mendel’s experiments became the basis for one of his theories of genetics known as the Theory of **SEGREGATION** ___ which states that diploid cells have “pairs” of genes for a given trait, are located on homologous chromosomes (one from mom and one from dad) and separate from each other during Meiosis so they end up in different gametes.__ __A. To get the most reliable data possible, he began by tracking genetic traits from one generation to the next where the parent generation differs in only one physical trait (such as purple flower verses white flower). This type of experiment is__ __called a__ **MONOHYBRID** __CROSS experiment.__ __ B. To better visualize the__ **PROBABILITY**_____ __or the likelihood of a possible outcome of a given__ __event expressed as a mathematical ratio, he used__ __a__ **PUNNETT** __SQUARE to show__ __the phenotype ratio (observed characteristics)__ __from the expected genotype possibilities.__ __C. For a monohybrid cross, draw four squares and__ __place the genotype of one parent on the top (one__ __allele above each column) and the genotype of__ __the other parent to the left of the table (one allele__ __before each row).__ **I can't draw it in, but the results are DD, Dd, DD, Dd.** __D. The diagram below shows that when a homozygous dominant parent “mates” with a homozygous recessive parent, 100% of the offspring will have a__ **HETEROZYGOUS** genotype. Since each gamete produced has a dominant allele, 100% will show the same dominant phenotype. 

E. The diagram below shows that when two heterozygous parents “mate” 25% (1/4) of the offspring will have a homozygous dominant genotype, 25% (1/4) of the offspring will have a homozygous recessive genotype, and 50% (1/2) will have a heterozygous genotype. Since the dominant allele is the one that always “shows itself”, 75% (3/4) will show the dominant phenotype, and 25% (1/4) will show the recessive phenotype. Remember, the recessive phenotype will only appear if there is no dominant allele present in the genotype of the organism.



F. To identify the unknown genotype of an organism that shows a dominant phenotype, Mendel conducted an experiment called a **TEST CROSS**, where the organism being studied was “mated” with an organism that had a recessive phenotype ( one with a **HOMOZYGOUS RECESSIVE** __genotype). In this case, any dominant trait that shows up must have come from the tested organism. If the tested organism was homozygous dominant, then 100% of the offspring will be heterozygous (Aa); if the organism was heterozygous, then only 50% of the offspring will be heterozygous (Aa) and 50% will be homozygous__ __recessive (aa).__ __4. Gregor Mendel also conducted experiments that became the basis for another of his__ __theories of genetics known as the Theory of__ **INDEPENDENT ASSORTMENT**_____ __which states that each allele for a specific trait (located on different homologous chromosomes) separate independently of each other. In other words, all of “dad’s” chromosomes don’t move together during Anaphase I of Meiosis. Some of the chromosomes go in one direction while others go the other direction.__ __A. To get the most reliable data possible, he tracked genetic traits from one generation to the next where the parent generation differs in__ two __physical traits, (where //two// pairs of genes were assorted into gametes), such as color of the__ __flower (purple verses white) and the height of the plant (short verses tall). This__ __type of experiment is called a__ **DIHYBRID** __CROSS experiment.__ __B. To draw a Punnett-square for this type of experiment there must be a total of 16 squares (four columns and four rows). The genotypes of the two traits for one parent are placed across the top of the diagram (genotypes of one trait are place above the first two columns and the genotype of the second trait are placed above the last two columns) and the genotypes of the two traits for the other parent are placed in front of the rows (genotypes of one trait are place before the first two rows and the genotype of the second trait are placed before the last two rows).__ __C. This type of experiment gives 16 different possible outcomes. This shows why when conducting experiments, try to keep the number of variables that are different as few as possible, preferrably only one variable different at a time.__ __5. While Mendel studied traits having clearly defined dominant or recessive forms, the expression of many traits is not as straightforward. There are several important dominance relations that are now known to exist.__ __A.__ **CODIMINANCE**___: occurs when the appearance of two dominant traits for a given allele can both be expressed in heterozygous chromosomes. In humans the best known example is with blood typing. On the red blood cells are special proteins called “immunoglobulins” that come in a recessive form or two dominant forms.__ __1. Type O: are homozygous recessive (ii)__ __2. Type A: are either homozygous dominant (IAIA ) or heterozygous (IAi)__ __3. Type B: are either homozygous dominant (IBIB) or heterozygous (IBi)__ __4. Type AB: are heterozygous dominant for BOTH (IAIB)__ __B.__ **INCOMPLETE DOMINANCE** __: occurs when the appearance is a “blending” of the dominant and recessive trait. An example is when a plant with a red flower is crossed with a plant with a white flower. Some of the resulting plants will have red flowers, others will have white flowers and still others will have pink flowers. Those with pink flowers demonstrate this phenomenon. In humans, curly hair is a dominant trait, while straight hair is recessive trait. People with a heterozygous genotype have naturally “wavy” hair.__ __C.__**EPISTASIS** is an interaction between the proteins produced by two or more gene pairs. The alleles of one gene may mask the expression of another gene’s alleles, so some phenotypes that would otherwise be expected may not express themselves. Hair color is one example. There is a gene that determines the __amount and type__ of melanin produced by body, and a second gene that determines __how much of the melanin will be absorbed__ by the hair. If a person can make the melanin, but is not able to deposit the melanin in the hair, the color will not show itself. D. **PLEIOTROPY**___ is when individual genes have positive or negative effects on two or more traits or in other words when the expression of an allele at a single location on a chromosome result in changes of two or more characteristic traits (phenotypes). One of the best examples in humans is the disease Sickle-cell anemia. There is a change in one specific nucleotide of the gene that contains the genetic instructions for the formation of the protein hemoglobin found in red blood cells. The condition results not only in how well the hemoglobin can deliver oxygen to the body cells, but it also changes the shape of the red blood cell causing them to get “stuck” in blood vessels leading to blood vessel blockages, that may lead to tissue or organ damage. Therefore a change in one trait, shows numerous changes or traits seen throughout the body.__

__E.__ _**CONTINUOUS VARIATION**__ ocurs if an observable trait is due to several genes, individuals of a population may show a wider range of possible phenotypes (eye color, hair color, height, etc.). The more genes involved in producing a given trait, the more environmental factors may influence the expression of the gene and therefore the more varied the possible outcomes.

6. This chapter discusses the basic principles of heredity and introduces the vocabulary of genetics. As a review, practice using the vocabulary by matching each phrase on the right with a word or phrase on the left. B. Homozygous C. Hybrid D. Genotype E. Segregation F. F2 generation G. True-breeding H. Heterozygous I. Dominant allele J. P generation K. Monohybrid cross L. Wild-type (pg. 194) M. Phenotype N. Cross O. F1 generation P. Recessive allele Q. Homologous chromosomes R. Genes S. Punnett square T. Diploid U. Locus || _**R** 1. A section of the DNA that determines specific heritable characteristics _**G** 2. Organisms that always produce offspring identical to parents _**C** 3. The offspring of two different varieties
 * A. Allele

_**P** 4. When two alleles of a pair are different, the one that is masked _**J** 5. Parent organisms that are mated

_**S** 6. A diagram that shows possible combinations of gametes _**K** 7. A breeding experiment that uses parents different in one characteristic _**A** 8. One of the alternative forms of a gene for a characteristic _**H** 9. An organism that has two different alleles for a characteristic _**D** 10. An organism’s genetic makeup

_**E** 11. Separation of allele pairs that occurs during gamete formation _**B** 12. An organism that has two identical alleles for a characteristic _**O** 13. Offspring of the P generation

_**L** 14. A characteristic most commonly found in nature _**M** 15. What an organism looks like; its expressed traits _**F** 16. Offspring of the F1 generation

_**N** 17. A hybridization

_**I** 18. When two alleles of a pair are different, the one that is expressed _**Q** 19. Where genes for a certain trait are located

_**T** 20. Term used to describe an organism with a pair of genes for each trait, one on each of two homologous chromosomes _**U** 21. Describes where a pair of genes for a particular trait are found on a chromosome. || 7. Demonstrate understanding of how to use a Punnett-square diagram to determine possible genotypes of children produced by two parents with known genotypes.Two apparently normal parents have the same genotypes and have been identified as “carriers” of the disease agammaglobulinemia, an inherited recessive defect of the immune system that is supposed to protect the body from infection. They gave birth to a child that did not have the disease and a daughter who suffers from the disease. A. What are the parents’ genotypes?
 * HETEROZYGOUS**

B. What is the genotype of the daughter who has agammaglobulinemia?
 * HOMOZYGOUS RECESSIVE**

C. Draw a Punnett square to show how two parents with a normal pheotype could have a child afflicted with a recessive inherited disease.


 * A a**
 * A AA Aa**
 * a Aa aa**

D. What was the probability that their daughter would have this disease?
 * 1/4 or one out of four probability.**

E. What was the probability that their daughter who did not have the disease is a carrier of the disease like the parents?
 * 2/3 or two out of three probability.**