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Basallo, Jacqueline Chapter 13 - (SELF MONITOR) Objectives 1. Explain why organisms only reproduce their own kind, and why offspring more closely resemble their parents than unrelated individuals of the same species. Life's most exclusive distinction is the ability of organisms to reproduce their own kind. Like begets like. Only oak trees produce oaks, and only elephants make elephants. Offspring more closely resemble their parents than unrelated individuals of the same species because parents pass on to their offspring discrete genes that retain their identity generation after generation. 2. Explain what makes heredity possible. The gene idea makes heredity possible. According to this model, parents pass on discrete heritable units that retain their separate identities in offspring. An organism's collection of genes can be sorted and passed along, generation after generation, in diluted form. 3. Distinguish between asexual and sexual reproduction. Asexual Reproduction: type of reproduction involving only one parent that produces genetically identical offspring by budding or by the division of a single cell or the entire organism into two parts or more. Sexual Reproduction: type of reproduction in which two parents give rise to offspring that have unique combinations of genes inherited from the gametes of two parents. 4. Diagram the human life cycle and indicate where in the human body that mitosis and meiosis occur; which cells are the result of meiosis and mitosis; and which cells are haploid. Figure 12.3, Page 228 The human life cycle. In each generation, the doubling of chromosome number that results from fertilization is offset by halving of chromosome number that results from meiosis. For humans, the number of chromosomes in a haploid cell is 23 (n=23); the number of chromosomes in the diploid cell zygote and all somatic cells arising from it is 46 (2n=46). 5. Distinguish among the life cycle patterns of animals, fungi, and plants. 6. List the phases of meiosis I and meiosis II and describe the events characteristic of each phase. I understand the concepts of Meiosis and the events that take place during each phase. 7. Recognize the phases of meiosis from diagrams or micrographs. I can recognize the phases of meiosis from diagrams or micrographs. 9. Describe the process of synapsis during prophase I, and explain how genetic recombination occurs. During Prophase 1 of meiosis, the duplicated chromosomes pair with their homologues, a process called synapsis. The four closely associated chromatids are visible in the light microscope as tetrads. 10. Describe key differences between mitosis and meiosis; explain how the end result of meiosis differs from that of mitosis. The key differences between mitosis and meiosis is: * Mitosis has one division, consisting of prophase, metaphase, anaphase and telophase. Meiosis has two divisions each consisting of prophase, metaphase, anaphase and telophase; DNA replication does not occur between the two divisions, and the homologous chromosomes synapse and form tetrads. *Mitosis has 2 daughter cells, each diploid and genetically identical to the mother cell. Meiosis has four daughter cells, each containing half as many chromosomes as the mother cell and they genetically un-identical to the mother cell and to each other. The end of meiosis differs from the end of mitosis in the at the end of meiosis, there is a production of gametes, the chromosome number reduces by half and it introduces genetic variability in the gametes. Mitosis develops of a multi-cellular adult from zygote and allows for the production of cells for growth and tissue repair. 11. Explain how independent assortment, crossing over, and random fertilization contribute to genetic variation in sexually reproducing organisms. The sexual processes that contribute to genetic variation in a population are independent assortment of chromosomes during meiosis 1, crossing over between homologous chromosomes during meiosis 1, and random fertilization of an ovum by a sperm. In independent variation, the positioning of each homologous pair of chromosomes is a matter of chance. This arrangement of chromosomes determines which chromosomes will be packed together in the haploid daughter cells. Crossing over is a process which produces individual chromosomes that combine genes inherited from two parents. Crossing over gives rise to individual chromosomes that have some combination of DNA originally derived from two different parents. 12. Explain why inheritable variation was crucial to Darwin's theory of evolution. Darwin’s theory of evolution was based on natural selection, in which the importance of genetic variation was recognized. This natural selection results in adaptation, the accumulation of those genetic variations that are favored by the environment. 13. List the sources of genetic variation. Sources of genetic variation are *independent assortment of homologous chromosome pairs during meiosis 1. *crossing over between homologous chromosomes during prophase 1 of meiosis 1. *Random fertilization of an ovum by a sperm. Chapter 14 - (SELF-MONITOR) Objectives 1. Describe the favored model of heredity in the 19th century prior to Mendel, and explain how this model was inconsistent with observations. The favored model of heredity in the 19th century prior to Mendel was the blending model, which was the idea that genetic material contributed by the two parents mixes in a manner analogous to the way blue and yellow paints blend to make green. This predicts that mating a blue parakeet with a yellow would for generations result in green offspring. The actual results of parakeet breeding contradict such prediction as well as also fails to explain other phenomena of inheritance, such as traits skipping a generation. 2. Explain how Mendel's hypothesis of inheritance differed from the blending theory of inheritance. An alternative to the blending model is Mendel’s gene idea. According to this model, parents pass on discrete heritable units that retain their separate identities in offspring. An organism's collection of genes can be sorted and passed along, generation after generation, in diluted form. 3. List several features of Mendel's methods that contributed to his success. Mendel began breeding garden peas in order to study inheritance. He chose to work with peas because they are available in many varieties. The use of peas also gave Mendel strict control over which plants mated with which. Mendel was careful to track the inheritance of only categorical variations, after cross pollination, making sure he started his experiments with varieties that were true-breeding. 4. List four components of Mendel's hypothesis that led him to deduce the law of segregation. 1. Alternative versions of genes account for variations in inherited characters 2. For each character, an organism inherits two alleles, one from each parent 3. If the two alleles differ, then one, the dominant allele is fully expressed in the organisms appearance, the other , the recessive allele, has no noticeable affect on the organisms appearance. 4. The two alleles for each character segregate during gamete production. 5. State, in their own words, Mendel's law of segregation. Two alleles for a character are packaged into separate independent gametes as each organism inherits one allele. 6. Use a Punnett square to predict the results of a monohybrid cross and state the phenotypic and genotypic ratios of the F2 generation. P P PP Pp p Pp pp p 7. Distinguish between genotype and phenotype; heterozygous and homozygous; dominant and recessive. phenotype: an organism’s appearance genotype: an organism’s genetic material homozygous: an organisms having a pair if identical alleles for a character heterozygous: an organism having a pair of two different alleles for a character dominant: the allele fully expressed in the organism’s appearance recessive: the allele that has no noticeable effect on the organism’s appearance 8. Explain how a testcross can be used to determine if a dominant phenotype is homozygous or heterozygous. A testcross is designed to reveal the genotype of an organism that exhibits a dominant trait, such as purple flowers in pea plants. The most efficient way to resolve the genotype is to cross the organism with an individual expressing the recessive trait. Since the genotypes of the white flowered plants, for example, must be homozygous, we can deduce the genotype of the purple-flowered parent by observing the phenotypes of the offspring. 9. Define random event, and explain why it is significant that allele segregation during meiosis and fusion of gametes at fertilization are random events. 10. Use the rule of multiplication to calculate the probability that a particular F2 individual will be homozygous recessive or dominant. The probability of an F2 plant having the genotype YYRR is 1/16 (1/4 chance for a YR ovum X 1/4 chance for a YR sperm. 11. Given a Mendelian cross, use the rule of addition to calculate the probability that a particular F2 individual will be heterozygous. We can calculate the probability of an F2 heterozygote as 1/4 +1 /4 = 1/2 12. Describe two alternate hypotheses that Mendel considered for how two characters might segregate during gamete formation, and explain how he tested those hypotheses. 1. For each character, an organism inherits two alleles, one from each parent. 2. Two alleles for each character segregate during gamete production. One test of Mendel’s segregation hypothesis is whether or not it can account for the 3:1 ratio he observed in the F2 generation of his numerous monohybrid crosses. When alleles segregate, half the gametes receive a purple-flower allele, while the other half get a white-flower allele. Using the Punnet square, a useful tool for showing all possible combinations of alleles in the offspring, each square represented an equally probable product of fertilization. This model accurately explains the 3:1 ratio that he observed in the F2 generations. 14. Use a Punnett square to predict the results of a dihybrid cross and state the phenotypic and genotypic ratios of the F2 generation. YR Yr yR yr YR YYRR YYRr YyRR YyRr Yr YYRr YYrr YyRr YyRr Yr YYRr YYrr YyRr Yyrr YR YYRR YYRr yYRR YyRr 16. Give an example of incomplete dominance and explain why it is not evidence for the blending theory of inheritance. An example of incomplete dominance is when red snapdragons are crossed with white snapdragons. TheF1 hybrids have pink flowers. Segregation of alleles into the gametes of the F1 plants result in an F2 generation with a 1:2:1 ration for both genotype and phenotype. 17. Explain how the phenotypic expression of the heterozygote is affected by complete dominance, incomplete dominance and co-dominance. The phenotypic expression of the heterozygote is affected by incomplete dominance by the F1 hybrids having an appearance somewhere in the middle of the phenotypes of the two parental varieties. In complete dominance, the phenotypic expression of the heterozygote is affected by the phenotype of the parental varieties being indistinguishable. In codominance, both alleles are separately manifested in the phenotype f the heterozygote. 18. Describe the inheritance of the ABO blood system and explain why the IA and IB alleles are said to be codominant. 19. Define and give examples of pleiotropy. Pleitropy is the ability of a gene to affect an organism in many ways. Alleles that are responsible for certain hereditary diseases in humans, including sickle cell anemia diseases, usually causing multiple symptoms are examples of Pleitropy. 20. Explain, in their own words, what is meant by "one gene is epistatic to another." By “one gene is epistatic to another” it is meant that a gene a specific region in a chromosome will alter the phenotypic expression of a gene on another region, thus, following an independent assortment. 23. Describe how environmental conditions can influence the phenotypic expression of a character. The environment can influence the phenotypic expression of a character by influencing quantitative characters. The environment affects the range of phenotypic possibilities over which there may be variation. Geneticists refer to these characters as multi-factorial, meaning that many factors, both genetic and environmental, collectively influence the phenotype. 24. Given a simple family pedigree, deduce the genotypes for some of the family members. I am familiarized with deducing the gentoypes for the family members of a family with a simple pedigree. Chapter 15 (SELF-MONITOR) Objectives 4. Define linkage and explain why linkage interferes with independent assortment. Genes located on the same chromosome tend to be inherited together in genetic crosses because they are a part of a single chromosome that is passed along as a unit. These are known as linked genes. Linked genes do not assort independently because they are located on the same chromosomes and tend to move together through meiosis and fertilization. 6. Explain how crossing over can unlink genes. Crossing over accounts for the recombination of linked genes. A crossover between homologous chromosomes breaks linkages in the parental chromosomes to form recombinant chromosomes that may bring together alleles in new combinations. 10. Describe sex determination in humans. The male carries X and Y chromosomes while the female carries two X chromosomes. When fertilization occurs, if a male's X chromosome unites with a female's X chromosome, the union produces a female. If this occurs with a male's Y chromosome, a male is produced. 11. Describe the inheritance of a sex-linked gene such as color-blindness. With color-blindness for example, a color-blind daughter may be born to a color-blind father whose mate is a carrier. However, because the sex-linked allele for color blindness is rare, the probability that such a man and woman will come together is very low. Sex-linked traits refers to X-linked traits. A mother may pass the gene to both her son and daughter while the father may only pass it on to their daughters. Females will only express the phenotype if homozygous recessive for the trait while any male receiving the trait from his mother will express the trait. 12. Explain why a recessive sex-linked gene is always expressed in human males. Recessive sex-linked genes are always expressed in human males because males lack the other X chromosome allowing them to be carriers of the genes. Whether recessive or dominant, the slight presence of a gene from a heterozygote mother would result in the male expressing the phenotype for the trait. 14. Distinguish among nondisjunction, and uploidy, and polyploidy; explain how these major chromosomal changes occur and describe the consequences. Nondisjunction is an accident of meiosis or mitosis, in which both members of a pair of homologous chromosomes or both sister chromatids fail to move apart properly. Aneuploidy is a chromosomal aberration in which certain chromosomes are present in extra copies or are deficient in number. Polyploidy is a chromosomal alteration in which the organism possesses more than two complete chromosome sets. 16. Distinguish among deletions, duplications, translocations, and inversions. Deletion is (1) a defficiency in a chromosome resulting from the loss of a fragment through a breakage, 2) a mutational loss of a nucleotide from a gene. Duplication is an aberration in chromosome structure resulting from an error in meiosis or mutagens; duplication of a portion of a chromosome resulting from fusion with a fragment from a homologous chromosome. Translocation is an aberration in chromosome structure resulting from an error in meiosis or from mutagens; attachment of a chromosomal fragment to a nonhomologous chromosome. (2) During protein synthesis, the third stage in the elongation cycle when the RNA carrying the growing polypeptide moves from the A site to the P site on the ribosome. (3) The transport via phloem of food in a plant Inversion is an aberration in chromosome structure resulting from an error in meiosis or from mutagens; reattachment in a reverse orientation of a chromosomal fragment to the chromosome from which the fragment originated.