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Virgin Birth of a Dragon




A reflection paper includes summarize which combines Chapter 8&9 together and self-reflect (how these two chapters can affect your life).;Attachments Preview;BSC1020_Chapter08_PPT.ppt Download Attachment;Chapter 8;Cellular Reproduction;Cells from Cells;BIOLOGY AND SOCIETY;Virgin Birth of a Dragon;In 2002, zookeepers at the Chester Zoo were;surprised to discover that their Komodo Dragon;laid eggs.;The female dragon had not been in the;company of a male.;The eggs developed without fertilization, in a;process called parthenogenesis.;DNA analysis confirmed that her offspring had;genes only from her.;A second European Komodo dragon is now known;to have reproduced;asexually, via parthenogenesis, and;sexually.;This species has;evolved the;potential to;undergo both;sexual and;asexual;reproduction;Figure 8.0;WHAT CELL REPRODUCTION;ACCOMPLISHES;Reproduction;May result in the birth of new organisms;More commonly involves the production of;new cells;When a cell undergoes reproduction, or cell;division, two daughter cells are produced that;are genetically identical to each other and to the;parent cell.;Before a parent cell splits into two, it duplicates its;chromosomes, the structures that contain most of the;organisms DNA.;During cell division, each daughter cell;receives one set of chromosomes.;Duplication;of all;chromosomes;Distribution via;mitosis;Chapter Review Figure;Genetically;identical;daughter cells;WHAT CELL REPRODUCTION;ACCOMPLISHES;Cell division plays important roles in the lives of;organisms. It;Replaces damaged or lost cells;Permits growth;Allows for reproduction;Video: Sea Urchin;Human kidney cell;LM;Colorized TEM;FUNCTIONS OF CELL DIVISION;Cell Replacement;Growth via Cell Division;Early human embryo;Figure 8.1;In asexual reproduction;Single-celled organisms reproduce by simple;cell division;There is no fertilization of an egg by a sperm;Some multicellular organisms, such as sea stars;can grow new individuals from fragmented;pieces.;Growing a new plant from a clipping is another;example of asexual reproduction.;In asexual reproduction, the lone parent and its;offspring have identical genes.;Mitosis is the type of cell division responsible;for;Asexual reproduction;Growth and maintenance of multicellular;organisms;LM;FUNCTIONS OF CELL DIVISION;Asexual Reproduction;Amoeba;Sea stars;African Violet;Figure 8.1;Sexual reproduction requires fertilization of an;egg by a sperm using a special type of cell;division called meiosis.;Thus, sexually reproducing organisms use;Meiosis for reproduction;Mitosis for growth and maintenance;THE CELL CYCLE AND MITOSIS;In a eukaryotic cell;Most genes are located on chromosomes in;the cell nucleus;A few genes are found in DNA in;mitochondria and chloroplasts;Eukaryotic Chromosomes;Each eukaryotic chromosome contains one very;long DNA molecule, typically bearing thousands;of genes.;The number of chromosomes in a eukaryotic cell;depends on the species.;Species;Indian muntjac deer;Koala;Opossum;Giraffe;Mouse;Human;Duck-billed platypus;Buffalo;Dog;Red viscacha rat;Number of chromosomes;in body cells;6;16;22;30;40;46;54;60;78;102;Figure 8.2;Chromosomes are made of a material called;chromatin;Chromatin consists of fibers composed of;roughly equal amounts of DNA and protein;molecules;The proteins help organize the chromatin;and help control the activity of its genes;As a cell prepares to divide, its chromatin fibers;coil up forming compact chromosomes;LM;Chromosomes;Figure 8.3;The DNA in a cell is packed into an elaborate;multilevel system of coiling and folding.;Histones are proteins used to package DNA in;eukaryotes.;The first level of packing is referred to as the;beads on a string arrangement;Each bead, called a nucleosome, consists;of DNA wound around histone molecules.;The next levels of packing, the beaded string is;wrapped into a tight helical fiber, which is then;looped and folded further into a supercoil;DNA double helix;Histones;TEM;Beads on;a string;Nucleosome;Figure 8.4;Tight helical fiber;Looped domains;TEM;Duplicated;chromosomes;(sister chromatids);Centromere;Figure 8.4;Before a cell divides, it duplicates all of its;chromosomes, resulting in two copies called sister;chromatids.;Sister chromatids are joined together at a narrow;waist called the centromere.;When the cell divides, the sister chromatids separate;from each other.;Once separated, each chromatid is;Considered a full-fledged chromosome;Identical to the original chromosome;Chromosome;duplication;Sister;chromatids;Chromosome;distribution to;daughter cells;Figure 8.5;Chapter;Review;Figure;Chromosome (one;long piece of DNA);Centromere;Sister;chromatids;Duplicated chromosome;The Cell Cycle;A cell cycle is the orderly sequence of events that;extend from the time a cell is first formed from a;dividing parent cell to its own division into two;cells.;The cell cycle consists of two distinct phases;Interphase;The mitotic phase;Most of a cell cycle is spent in interphase.;During interphase, a cell;Performs its normal functions;Doubles everything in its cytoplasm;Grows in size;Interphase is divided into three stages;G1 (Gap 1): Cell is growing and preparing;for DNA synthesis;S (Synthesis): Chromosomes are duplicated;G2 (Gap 2): Cell is growing and preparing;for cell division;S phase (DNA synthesis;chromosome duplication);Interphase: metabolism and;growth (90% of time);G1;Cytokinesis;(division of;cytoplasm);Mitotic (M) phase;cell division;(10% of time);G2;Mitosis;(division of nucleus);Figure 8.6;The mitotic (M) phase includes two overlapping;processes;Mitosis, in which the nucleus and its contents;divide evenly into two daughter nuclei;Cytokinesis, in which the cytoplasm is;divided in two;Video: Sea Urchin (time lapse);Mitosis and Cytokinesis;During mitosis the mitotic spindle, a footballshaped structure of microtubules, guides the;separation of two sets of daughter chromosomes.;Spindle microtubules grow from two;centrosomes, clouds of cytoplasmic material that;in animal cells contain centrioles.;Mitosis consists of four distinct phases;(A) Prophase;(B) Metaphase;(C) Anaphase;(D) Telophase;Please refer to pp. 126-127 in your textbook for;detailed discussion of these phases;BioFlix Animation: Mitosis;INTERPHASE;Centrosomes;(with centriole pairs);Chromatin;PROPHASE;Fragments of;Early mitotic;Centrosome nuclear envelope;spindle;Centromere;Spindle;microtubules;LM;Chromosome, consisting;Nuclear Plasma;envelope membrane of two sister chromatids;Figure 8.7;METAPHASE;ANAPHASE;TELOPHASE & CYTOKINESIS;Nuclear;envelope;forming;Spindle;Cleavage;furrow;Daughter;chromosomes;Figure 8.7;Cytokinesis typically;Occurs at the end of telophase;Divides the cytoplasm;Is different in plant and animal cells;Video: Animal Mitosis;Blast Animation: Cytokinesis in Plant Cells;In animal cells, cytokinesis is known as cleavage and;It begins with the appearance of a cleavage furrow;an indentation at the equator of the cell.;In plant cells, cytokinesis begins when vesicles;containing cell wall material collect at the middle of the;cell and then fuse;This leads to the formation of a membranous disk;called the cell plate.;SEM;Cleavage;furrow;Cleavage furrow;Contracting ring of;microfilaments;Daughter cells;Figure 8.8;Cell plate Daughter;forming nucleus;Figure 8.8;LM;Wall of;parent cell;Cell wall;Vesicles containing;Cell plate;cell wall material;New cell wall;Daughter cells;Cancer Cells: Growing Out of Control;Normal plant and animal cells have a cell cycle;control system that consists of specialized;proteins, which send stop and go-ahead;signals at certain key points during the cell cycle.;What Is Cancer?;Cancer is a disease of the cell cycle.;Cancer cells do not respond normally to the cell;cycle control system.;They divide excessively and can invade other;tissues of the body;Cancer cells can form a tumor, an abnormally;growing mass of body cells.;In benign tumors, the abnormal cells remain at;their original site;Malignant tumors can spread to neighboring;tissues and interrupt normal body functions;A person with a malignant tumor is said to have;cancer.;The spread of cancer cells beyond their original site;of origin is metastasis.;Lymph;vessels;Tumor;Blood;vessel;Glandular;tissue;A tumor grows;from a single;cancer cell.;Cancer cells invade;neighboring tissue.;Metastasis: Cancer;cells spread through;lymph and blood;vessels to other parts;of the body.;Figure 8.9;Cancer Treatment;The three main types of cancer treatment are;referred to as slash, burn, and poison;These are in order;Surgery, which removes the tumor;Radiation therapy, which damages DNA;and disrupts cell division;Chemotherapy, which uses drugs that;disrupt cell division;Cancer Prevention and Survival;Certain behaviors can decrease the cancer risk;Not smoking;Exercising adequately;Avoiding exposure to the sun;Eating a high-fiber, low-fat diet;Performing self-exams;Regularly visiting a doctor to identify tumors;early;Meiosis, the Basis of Sexual Reproduction;Sexual reproduction;Depends on meiosis;and fertilization;Produces offspring;that contain a unique;combination of genes;from the parents;Figure 8.10;Homologous Chromosomes;Different individuals of a single species have the;same number and types of chromosomes.;A human somatic cell is a typical body cell;Has 46 chromosomes;A karyotype is an image that reveals an orderly;arrangement of chromosomes.;Homologous chromosomes are matching pairs;of chromosomes that can possess different;versions of the same genes.;LM;Pair of homologous;chromosomes;Centromere;Sister;chromatids;One duplicated;chromosome;Figure 8.11;Altogether, humans have 23 pairs of homologous;chromosomes;A pair of sex chromosomes;Females have two X chromosomes, while;males have an X and a Y chromosome;Twenty-two pairs of matching chromosomes;called autosomes;We inherit one chromosome of each pair from our;mother and the other from our father;Gametes and the Life Cycle of a Sexual Organism;The life cycle of a multicellular organism is the;sequence of stages leading from the adults of one;generation to the adults of the next.;Having two sets of chromosomes, one from each;parent, is a key factor in the life cycle of humans;and all other species that reproduce sexually;Figure 8.12;Haploid gametes (n = 23);Egg cell;n;n;Sperm cell;FERTILIZATION;MEIOSIS;Multicellular;diploid adults;(2n = 46);2n;MITOSIS;and development;Diploid;zygote;(2n = 46);Key;Haploid (n);Diploid (2n);Humans are diploid organisms in which;Their somatic cells contain two sets of;chromosomes;Their gametes are haploid, having only one;set of chromosomes;In humans, a haploid sperm fuses with a haploid;egg during fertilization to form a diploid zygote.;Sexual life cycles involve an alternation of;diploid and haploid stages.;Meiosis produces haploid gametes, which keeps;the chromosome number from doubling every;generation.;Chromosomes;duplicate.;Homologous;chromosomes;separate.;Sister;chromatids;separate.;Pair of homologous;chromosomes in;diploid parent cell;Duplicated pair;of homologous;chromosomes;INTERPHASE BEFORE MEIOSIS;Sister;chromatids;MEIOSIS I;MEIOSIS II;Figure 8.13;The Process of Meiosis;In meiosis;Haploid daughter cells are produced in diploid;organisms;Interphase is followed by two consecutive;divisions, meiosis I and meiosis II;Crossing over occurs;This is an exchange of genetic material;between homologous chromosomes;BioFlix Animation: Meiosis;MEIOSIS I: HOMOLOGOUS CHROMOSOMES SEPARATE;INTERPHASE;Centrosomes;(with centriole;pairs);Nuclear;envelope;Chromatin;Chromosomes;duplicate.;PROPHASE I;Sites of;crossing over;Spindle;Sister;chromatids;Pair of;homologous;chromosomes;Homologous;chromosomes;pair up and;exchange;segments.;METAPHASE I;Microtubules;attached;to chromosome;ANAPHASE I;Sister chromatids;remain attached;Centromere;Pairs of;homologous;chromosomes;line up.;Pairs of;homologous;chromosomes;split up.;Figure 8.14;INTERPHASE;Centrosomes;(with centriole;pairs);Nuclear envelope;Chromatin;PROPHASE I;METAPHASE I;Sites of crossing over;Microtubules attached;to chromosome;Spindle;Sister;chromatids;Centromere;Pair of;homologous;chromosomes;ANAPHASE I;Sister chromatids;remain attached;TELOPHASE I & CYTOKINESIS;Cleavage;furrow;MEIOSIS II: SISTER CHROMATIDS SEPARATE;TELOPHASE I;AND;CYTOKINESIS;PROPHASE II;METAPHASE II;ANAPHASE II TELOPHASE II;AND;CYTOKINESIS;Cleavage;furrow;Sister;chromatids;separate;Two haploid;cells form;chromosomes;are still;doubled.;Haploid;daughter;cells forming;During another round of cell division, the sister;chromatids finally separate, four haploid;daughter cells result, containing single;chromosomes.;PROPHASE II;METAPHASE II;ANAPHASE II;Sister chromatids;separate;TELOPHASE II;CYTOKINESIS;Haploid;daughter cells;forming;Review: Comparing Mitosis and Meiosis;In mitosis and meiosis, the chromosomes;duplicate only once, during the preceding;interphase.;The number of cell divisions varies;Mitosis uses one division and produces two;diploid cells;Meiosis uses two divisions and produces four;haploid cells;All the events unique to meiosis occur during;meiosis I.;Pairing of homologous chromosomes;Crossing-over;Meiosis II is virtually identical to mitosis in that;it separates sister chromatids;But unlike mitosis, meiosis II yields daughter;cells with a haploid set of chromosomes;MITOSIS;MEIOSIS;Prophase I;Prophase;Chromosome;duplication;Duplicated chromosome;(two sister chromatids);Chromosome;duplication;Parent cell;(before chromosome duplication);2n = 4;Homologous;chromosomes come;together in pairs.;Metaphase;MEIOSIS I;Site of crossing;over between;homologous;(nonsister);chromatids;Metaphase I;Chromosomes;align at the;middle of the;cell.;Homologous;pairs align at;the middle;of the cell.;Figure 8.15;Anaphase I;Telophase I;Anaphase;Telophase;2n;Sister;chromatids;separate;during;anaphase.;Daughter cells;of mitosis;2n;Homologous;chromosomes;separate during;anaphase I;sister chromatids;remain together.;Chromosome with;2 sister chromatids;Daughter;cells of;meiosis I;Haploid;n= 2;MEIOSIS II;Sister chromatids;separate during;anaphase II.;n;n;n;n;Daughter cells of meiosis II;MEIOSIS;MITOSIS;Parent;cell (2n);Parent;cell (2n);Chromosome Chromosome;duplication;duplication;MEIOSIS I;Pairing of;homologous;chromosome;Crossing over;2n;Daughter;cells;2n;MEIOSIS II;n;n;n;n;Daughter cells;The Origins of Genetic Variation;Offspring of sexual reproduction are genetically;different from their parents and one another.;As will be discussed later, this genetic variety in;offspring is the raw material for natural selection;Independent Assortment of Chromosomes;When aligned during metaphase I of meiosis, the;side-by-side orientation of each homologous pair;of chromosomes is a matter of chance.;Every chromosome pair orients independently of;the others during meiosis.;For any species the total number of chromosome;combinations that can appear in the gametes due;to independent assortment is;2n where n is the haploid number.;For a human, n = 23;223 = 8,388,608 different chromosome;combinations possible in a gamete;Blast Animation: Genetic Variation: Independent Assortment;POSSIBILITY 2;POSSIBILITY 1;Two equally probable;arrangements of;chromosomes;at metaphase of;meiosis I;Metaphase;of;meiosis II;Gametes;Combination a;Combination b;Combination c Combination d;Because possibilities 1 and 2 are equally likely, the four possible types;Of gametes will be made in approximately equal numbers.;Random Fertilization;A human egg cell is fertilized randomly by one;sperm, leading to genetic variety in the zygote.;If each gamete represents one of 8,388,608;different chromosome combinations, at;fertilization, humans would have 8,388,608;8,388,608, or more than 70 trillion, different;possible chromosome combinations!;Note: If crossing-over is considered, the number;is even much higher than that;The process of fertilization: a close up view;Figure 8.17;Crossing Over;In crossing over, nonsister chromatids of;homologous chromosomes exchange;corresponding segments;This leads to genetic recombination, or the;production of gene combinations different;from those carried by parental chromosomes;Blast Animation: Genetic Variation: Fusion of Gametes;Prophase I;of meiosis;Duplicated pair of;homologous;chromosomes;Homologous chromatids;exchange corresponding;segments.;Chiasma, site of;crossing over;Metaphase I;Sister chromatids;remain joined at their;centromeres.;Spindle;microtubule;Metaphase II;Gametes;Recombinant chromosomes;combine genetic information;from different parents.;Recombinant chromosomes;Figure 8.18;Prophase I of meiosis;Homologous;chromatids exchange;corresponding;segments.;Duplicated pair;of homologous;chromosomes;Chiasma, site of;crossing over;Metaphase I;Sister chromatids;remain joined at their;centromeres.;Spindle;microtubule;Metaphase II;Gametes;Recombinant;chromosomes combine;genetic information;from different parents.;Recombinant chromosomes;The Process of Science;Do All Animals Have Sex?;Observation: No scientists have ever found male;bdelloid rotifers, a microscopic freshwater;invertebrate.;Question: Does this;entire class of animals;reproduce solely by;asexual means?;Figure 8.19;The Process of Science;Do All Animals Have Sex?;Hypothesis: Bdelloid rotifers have thrived for;millions of years using only asexual;reproduction.;Prediction: Bdelloid rotifers would display;much more variation in their homologous pairs of;genes than most organisms.;Experiment: Researchers compared sequences;of a particular gene in bdelloid and non-bdelloid;rotifers.;Results;Non-bdelloid sexually reproducing rotifers;had nearly identical homologous genes;Bdelloid asexually reproducing rotifers had;homologous genes that differed by 3.554%.;Conclusion: Bdelloid rotifers have evolved for;millions of years without any sexual;reproduction.;When Meiosis Goes Awry;What happens when errors occur in meiosis?;Such mistakes can result in genetic abnormalities;that range from mild to fatal.;How Accidents during Meiosis Can Alter;Chromosome Number;In nondisjunction;the members of a chromosome pair fail to;separate during anaphase;thus producing gametes with an incorrect;number of chromosomes.;Nondisjunction can occur during meiosis I or II.;NONDISJUNCTION IN MEIOSIS I;NONDISJUNCTION IN MEIOSIS II;Meiosis I;Nondisjunction;Pair of homologous;chromosomes fails;to separate.;Meiosis II;Nondisjunction;Pair of sister;chromatids;fails to separate.;Gametes;n+ 1;n+ 1;n1;Abnormal gametes;n 1 Number of n + 1;chromosomes;n1;n;n;Abnormal gametes Normal gametes;Figure 8.20;If nondisjunction occurs, and a normal sperm;fertilizes an egg with an extra chromosome, the;result is a zygote with a total of 2n + 1;chromosomes.;If the organism survives, it will have an;an abnormal karyotype and;probably a syndrome of disorders caused by;the abnormal number of genes.;Figure 8.21;Abnormal egg;cell with extra;chromosome;n+ 1;Normal;sperm cell;n (normal);Abnormal zygote;with extra;chromosome 2n + 1;Down Syndrome: An Extra Chromosome 21;Down Syndrome;Is also called trisomy 21;Is a condition in which an individual has an;extra chromosome 21;Affects about one out of every 700 children;LM;Chromosome 21;Figure 8.22;Incidence of Down Syndrome increases with moms age;Infants with Down syndrome;(per 1,000 births);90;80;70;60;50;40;30;20;10;0;20;25;30;35;40;Age of mother;45;50;Figure 8.23;Abnormal Numbers of Sex Chromosomes;Nondisjunction can also affect the sex;chromosomes (X and Y);However, they seem to upset the genetic;balance less than unusual no. of autosomes;Evolution Connection: The Advantages of Sex;Asexual reproduction conveys an evolutionary;advantage when plants are;Sparsely distributed;Superbly suited to a stable environment;Asexual reproduction also eliminates the need to;expend energy;forming gametes and;copulating with a partner.;Figure 8.24;Runner;Many plants, such as this strawberry, have the;ability to reproduce both sexually (via flowers;that produce fruit) and asexually (via runners);Evolution Connection: The Advantages of Sex;In contrast to plants, the vast majority of animals;reproduce by sexual means;Sexual reproduction may convey an evolutionary;advantage by;1) Speeding adaptation to a changing;environment, and thus enhancing survival;2) Allowing a population to more easily rid itself;of harmful genes;View Full Attachment;BSC1020_Chapter09_PPT.ppt Download Attachment;Chapter 9;Patterns of Inheritance;BIOLOGY AND SOCIETY;Our Longest-Running Genetics Experiment: Dogs;People have selected and mated dogs with;preferred traits for more than 15,000 years.;Over thousands of years, such genetic tinkering;has led to the incredible variety of body types;and behaviors in dogs today.;The biological principles;underlying genetics have;only recently been;understood;Figure 9.0;HERITABLE VARIATION AND PATTERNS;OF INHERITANCE;Heredity is the transmission of traits from one;generation to the next.;Genetics is the scientific;study of heredity;Gregor Mendel (1860s);First person to analyze;patterns of inheritance;Deduced the fundamental;principles of genetics;Figure 9.1;In an Abbey Garden;Mendel studied garden peas because they;Were easy to grow;Came in many readily distinguishable;varieties;Are easily manipulated;Can self-fertilize;Petal;Stamen;(makes spermproducing;pollen);Carpel;(produces eggs);Figure 9.2;A character is a heritable feature that varies;among individuals.;A trait is a variant of a character.;Each of the characters Mendel studied occurred;in two distinct forms.;Mendel;Created true-breeding varieties of plants;Crossed two different true-breeding varieties;Hybrids are the offspring of two different truebreeding varieties.;The parental plants are the P generation.;Their hybrid offspring are the F1 generation.;A cross of the F1 plants forms the F2;generation.;Removed;stamens;from purple;flower.;Stamens;Parents;(P);Carpel;Transferred pollen from;stamens of white flower;to carpel of purple flower.;Pollinated carpel;matured into pod.;Offspring;(F1);Planted seeds;from pod.;Figure 9.3;Mendels Law of Segregation;Mendel performed many experiments.;He tracked the inheritance of characters that;occur as two alternative traits.;The results led him to formulate several;hypotheses about inheritance;Dominant Recessive;Flower color;Dominant;Recessive;Pod shape;Purple;White;Flower position;Inflated;Constricted;Pod color;Green;Yellow;Tall;Dwarf;Stem length;Axial;Terminal;Yellow;Green;Round;Wrinkled;Seed color;Seed shape;Figure 9.4;Monohybrid Crosses;A monohybrid cross is a cross between two;true-breeding parent plants that differ in only;one character.;Blast Animation: Single-Trait Crosses;P Generation;(true-breading;parents);Purple flowers;F1 Generation;White flowers;All plants have;purple flowers;Fertilization;among F1 plants;(F1 F1);F2 Generation;3;of plants;4;have purple flowers;1;of plants;4;have white flowers;Figure 9.5;Mendel developed four hypotheses from the;monohybrid cross;1. There are alternative versions of genes, called;alleles.;2. For each character, an organism inherits two;alleles, one from each parent.;An organism is homozygous for that gene;if both alleles are identical.;An organism is heterozygous for that gene;if the alleles are different.;3. If two alleles of an inherited pair differ;The allele that determines the organisms;appearance is the dominant allele;The other allele, which has no noticeable;effect on the appearance, is the recessive;allele;4. Gametes carry only one allele for each;inherited character.;The two members of an allele pair;segregate (separate) from each other during;the production of gametes.;This statement is the law of segregation.;Do Mendels hypotheses account for the 3:1 ratio;he observed in the F2 generation?;A Punnett square highlights the four possible;combinations of gametes and offspring that result;from each cross.;Blast Animation: Genetic Variation: Fusion of Gametes;P Generation;Genetic makeup (alleles);Purple flowers;Alleles carried PP;by parents;Gametes;White flowers;pp;All p;All P;F1 Generation;(hybrids);Alleles;segregate;Purple flowers;All Pp;F2 Generation;(hybrids);Sperm from;F1 plant;p;P;1;Gametes 2 P;P;Eggs from;F1 plant;p;1 p;2;PP;Pp;Pp pp;Phenotypic ratio;Genotypic ratio;3 purple: 1 white 1 PP: 2 Pp: 1 pp;Figure 9.6;P Generation;Genetic makeup (alleles);Purple flowers;Alleles carried;PP;by parents;Gametes;All P;White flowers;pp;All p;F1 Generation;(hybrids);Purple flowers;All Pp;Alleles;segregate;1;2;Gametes;1;2;P;p;Sperm from F1 plant;p;P;F2 Generation;(hybrids);Eggs from;F1 plant;P;PP;Pp;p;Pp;pp;Phenotypic ratio Genotypic ratio;3 purple: 1 white 1 PP: 2 Pp: 1 pp;Summary: Law of Segregation;Fertilization;Alleles;Meiosis;Diploid cell;(contains paired;alleles, alternate;forms of a gene);Gamete;from other;parent;Haploid gametes;(allele pairs separate);Chapter Review Figure;Diploid zygote;(contains;paired alleles);Geneticists distinguish between an organisms;physical traits and its genetic makeup.;An organisms physical traits are its;phenotype.;An organisms genetic makeup is its;genotype.;Genetic Alleles and Homologous Chromosomes;A gene locus is a specific location of a gene;along a chromosome;Homologous chromosomes have;Genes at specific loci;Alleles of a gene at the same locus;Gene loci;Dominant;allele;P;Genotype;a;B;P;Homologous;chromosomes;a;b;Recessive;allele;Bb;PP;aa;Homozygous;Homozygous;Heterozygous;for the;for the;dominant allele recessive allele;Figure 9.7;Mendels Law of Independent Assortment;A dihybrid cross is the crossing of parental;varieties differing in two characters.;What would result from a dihybrid cross? Two;hypotheses are possible;1. Dependent assortment;2. Independent assortment;Blast Animation: Two-Trait Crosses;(a) Hypothesis: Dependent assortment;P Generation;RRYY;(b) Hypothesis: Independent assortment;RRYY;rryy;Gametes RY;ry;rryy;Gametes RY;ry;Figure 9.8;F1 Generation;RrYy;RrYy;Sperm;F2 Generation;1;1 rY;RY;4;4;Sperm;1;2 RY;1;ry;2;1;2 RY;1 Ry 1;ry;4;4;1;RY;4;RRYY RrYY RRYy RrYy;1;rY;4;RrYY rrYY;1;ry;2;Predicted results;(not actually seen);RrYy rrYy;9;16;1 Ry;4;RRYy RrYy RRyy Rryy;3;16;1 ry;4;Eggs;3;16;1;16;Eggs;RrYy rrYy Rryy rryy;Actual results;(support hypothesis);Yellow;round;Green;round;Yellow;wrinkled;Green;wrinkled;(a) Hypothesis: Dependent assortment;F2 Generation;1;2;Sperm;RY;1;2;ry;1;2;RY;Eggs;1;2;ry;Predicted results;(not actually seen);(b) Hypothesis: Independent assortment;1;4;1;RY;4;1;4;rY;Eggs;1;4;Ry;1;4;ry;Sperm;RY;1;4;rY;1;4;Ry;1;4;ry;F2 Generation;RRYY RrYY RRYy RrYy;RrYY rrYY RrYy rrYy;9;16;Yellow;round;RRYy RrYy RRyy Rryy;3;16;Green;round;3;16;Yellow;wrinkled;1;16;Green;wrinkled;RrYy rrYy Rryy;rryy;Actual results;(support hypothesis);Figure 9.8;Mendels dihybrid cross supported the;hypothesis that each pair of alleles segregates;independently of the other pairs during gamete;formation.;Thus, the inheritance of one character has no;effect on the inheritance of another.;This is the law of independent assortment.;Independent assortment is also seen in two;hereditary characters in Labrador retrievers.;Blind dog;Phenotypes;Genotypes;Black coat;normal vision;B_N;Black coat;blind (PRA);B_nn;Blind dog;Chocolate coat, Chocolate coat;blind (PRA);normal vision;bbnn;bbN;(a) Possible phenotypes of Labrador retrievers;Figure 9.9;(b) A Labrador dihybrid cross Mating of double heterozygotes;(black coat, normal vision) (BbNn BbNn);Blind;9 black coat;normal vision;3 black coat;blind (PRA);Blind;3 chocolate coat;normal vision;1 chocolate coat;blind (PRA);Using a Testcross to Determine an Unknown;Genotype;A testcross is a mating between;an individual of dominant phenotype (but;unknown genotype) and;a homozygous recessive individual;Figure 9.10;Testcross;Genotypes;B;bb;Two possible genotypes for the black dog;BB;Gametes;B;Offspring;b Bb;All black;or;Bb;B;b;b Bb bb;1 black: 1 chocolate;Chapter Review Figure;Phenotype;Genotype;Dominant;P?;Recessive;pp;or;Phenotype;All dominant;Conclusion;Unknown parent;is PP;1 dominant: 1 recessive;Unknown parent;is Pp;The Rules of Probability;Mendels strong background in mathematics;helped him understand patterns of inheritance.;The rule of multiplication states that the;probability of a compound event is the product of;the separate probabilities of the independent;events.;This rule holds true for independent events that;occur in genetics (e.g. a cross of two heterozygote;black Labs) as well as coin tosses, as shown in;Figure 9.11;F1 Genotypes;Bb female;Bb male;Formation of eggs;Formation of sperm;F2 Genotypes;Male;gametes;Female gametes;1;2;Figure;9.11;1;2;B;B;B;B;1;2;b;1;4;1;4;((1 1));x;2 2;1;2;b;B;b;1;4;b;B;b;b;1;4;Family Pedigrees;Mendels principles apply to the inheritance of;many human traits.;Figure 9.12 shows examples of inherited human;traits thought to be controlled by a single gene;DOMINANT TRAITS;Widows peak;Free earlobe;No freckles;Straight hairline;Attached earlobe;RECESSIVE TRAITS;Freckles;Figure 9.12;Dominant traits are not necessarily;normal or;more common;Wild-type traits are;those seen most often in nature and;not necessarily specified by dominant alleles;A family pedigree;Shows the history of a trait in a family;Allows geneticists to analyze human traits;To analyze a pedigree, a geneticist applies logic;and Mendels laws;First generation;(grandparents);Second generation;(parents, aunts, and;uncles);Third generation;(brother and;sister);Female Male;Attached;Free;Ff;FF;or;Ff;ff;ff;Ff;Ff;Ff;ff;ff;FF;or;Ff;Ff;ff;Figure 9.13;Human Disorders Controlled by a Single Gene;Many human traits;Show simple inheritance patterns;Are controlled by single genes on autosomes;Recessive Disorders;Most human genetic disorders are recessive.;Individuals who have the recessive allele but;appear normal are carriers of the disorder.;Indeed, most people who have recessive;disorders are born to normal parents who are;both carriers;Parents;Hearing;Dd;Hearing;Dd;Offspring;D Sperm d;D;DD;Hearing;Dd;Hearing;(carrier);Dd;Hearing;(carrier);dd;Deaf;Eggs;d;Figure 9.14;Cystic fibrosis;Is the most common lethal genetic disease in;the United States;Is caused by a recessive allele carried by;about one in 31 Americans;Prolonged geographic isolation of certain;populations can lead to inbreeding, the mating;of close relatives.;Inbreeding increases the chance of offspring;homozygous for a harmful recessive trait.;Dominant Disorders;Some human genetic disorders are dominant.;Huntingtons disease, which leads to degeneration;of the nervous system, does not usually begin until;middle age.;Achondroplasia is a form;of dwarfism.;The homozygous;dominant genotype;causes death of the embryo.;Thus, only heterozygotes;have this disorder.;Figure 9.15;Figure 9.16a;Parents;Normal;(no achondroplasia);dd;d;D;Dwarf;(achondroplasia);Dd;Sperm;d;Dd;Dwarf;Dd;Dwarf;dd;Normal;dd;Normal;Eggs;d;Figure 9.16b;Molly Jo;Jeremy;Jacob;Zachary;Amy;Matt;;The Process of Science;What Is the Genetic Basis of Coat Variation in Dogs?;Observation: Dogs come in a wide variety of;physical types.;Question: What is the genetic basis for canine;coats?;Hypothesis: A comparison of genes of a wide;variety of dogs with different coats would;identify the genes responsible.;Prediction: A mutation in just a few genes;account for the coat appearance.;Experiment: Compared DNA sequences of 622;dogs from dozens of breeds.;Results: Three genes in different combinations;produced seven different coat appearances, from;very short hair to full, thick, wired hair.;Figure 9.17;Genetic Testing;Today many tests can detect the presence of;disease-causing alleles.;Most genetic testing is performed during;pregnancy.;Amniocentesis collects cells from amniotic fluid.;Chorionic villus sampling removes cells from;placental tissue.;Genetic counseling helps patients understand the;results and implications of genetic testing.;VARIATIONS ON MENDELS LAWS;Mendels laws are valid for all sexuallyreproducing species;However, Mendels laws do not explain some;patterns of genetic inheritance;In particular, the many cases of inherited;characters that exist in more than two-clear;variants;Incomplete Dominance in Plants and People;In incomplete dominance, F1 hybrids have an;appearance in between the phenotypes of the two;parents.;For example, when red snapdragons are crossed;with white snapdragons, all the F1 hybrids have;pink flowers;P Generation;White;rr;Red;RR;Gametes;R;r;F1 Generation;Pink;Rr;Gametes 1 R 1 r;2;2;F2 Generation;1 R;2;Eggs;1 r;2;Sperm;1;1;R 2 r;2;RR;Rr;Rr;rr;Figure 9.18;Chapter Review Figure;Dominant phenotype;(RR);Recessive phenotype;(rr);Intermediate phenotype;(incomplete dominance);(Rr);Hypercholesterolemia;Is characterized by dangerously high levels of;cholesterol in the blood.;Is a human trait that is incompletely dominant.;Heterozygotes have blood cholesterol levels;about twice normal.;Homozygotes have blood cholesterol levels;about five times normal, and may have


Paper#18020 | Written in 18-Jul-2015

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