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UNIT 3 ALL ORGANISMS NEED TO REPRODUCE, BUT WHY? What is Involved in the Reproduction of Humans? Types of Reproduction ________________________ reproduction __________________________ are duplicated and cell divides Each daughter cell is genetically ________________________ to the parent and the other daughter _______________________ reproduction Each offspring inherits a unique __________________________ of genes from both parents Offspring can show great ____________________________ In order to get a good grasp of both sexual and asexual reproduction we must first begin with understanding how cells reproduce. Understanding of the _____________________________, which includes ___________________________, will greatly increase your understanding if both sexual and asexual reproduction The Cell Cycle The cell cycle is defined as There are two phases of the cell cycle __________________________________ (cell growth and copying of chromosomes in preparation for cell division) ______________________ (M) phase (_______________________) (mitosis and cytokinesis) Interphase (about ____% of the cell cycle) can be divided into subphases _________ phase (“first gap”) _________ phase (“synthesis”) _________ phase (“second gap”) The cell grows during all three phases, but chromosomes are duplicated only during the S phase The Key Roles of Cell Division The ability of organisms to produce more of their own kind best distinguishes __________________ things from nonliving matter The continuity of life is based on the reproduction of cells, or _______________________ In unicellular organisms, division of one cell reproduces the entire organism Multicellular organisms depend on cell division for Most Cell Division results in Genetically Identical Daughter Cells Most cell division results in daughter cells with identical genetic information, ___________ _______________________ cells (nonreproductive cells) have two sets of chromosomes The exception is ___________________, a special type of division that can produce sperm and egg cells Gametes (reproductive cells: sperm and eggs) Cellular Organization of the Genetic Material All the DNA in a cell constitutes the cell’s ____________________ A genome can consist of a single DNA molecule (common in prokaryotic cells) or a number of DNA molecules (common in eukaryotic cells) There are several terms used to describe the genetic material in the cell Chromatin and Chromosome ___________________________ is uncondensed complex of DNA and associated proteins that is typical of the genetic material during interphase of the cell cycle It eventually will condenses during cell division and become ________________________ Chromatids ___________________________ are similar to chromosomes in that they are condensed DNA molecules but they are attached to their identical at a _______________________ In preparation for cell division, DNA is _______________ The entire structure is called a _________________________________ (one being the original DNA and the other being the copy) During cell division, Once separate, the chromatids are called _______________________________ Eukaryotic cell division/mitotic phase consists of _________________________, the division of the ____________________________ in the nucleus _________________________, the division of the _______________________________ Mitosis is conventionally divided into five phases Before we get to the stages of Mitosis lets quickly review Interphase _______________________________: Duplication of the genetic material ends when chromosomes begin to become visible _______________________________ (the first stage of mitosis): The genetic material begins to _______________________. The mitotic ______________________ is forming. ______________ migrate to opposite ends of the cell ______________________________: Chromatin completely coil into chromosomes and then produce sister chromatids; nucleoli and nuclear membrane __________________ ______________________________: The spindle is fully formed; sister chromatids are aligned _____________________ file with centromeres on the metaphase plate ______________________________: Sister chromatids ___________________________ from the centromere, dividing to arrive at opposite _________________ Genetic material is now called? ______________________________: Cell elongation continues, a nuclear envelope forms around chromosomes, chromosomes uncoil, and nucleoli reappear ______________________________: The cytoplasm _________________________ Cytokinesis In animal cells, cytokinesis occurs by a process known as ______________________, forming a ___________________________________ In plant cells, a __________________________________ forms during cytokinesis How is the Cell Cycle Regulated? The frequency of cell division _______________ with the _______________ of cell These differences result from regulation at the molecular level Cancer cells manage to escape the usual _________________________ on the cell cycle The Cell Cycle Control System The sequential events of the cell cycle are directed by a distinct ______________________________, which is similar to a clock The clock has specific ___________________________ where the cell cycle stops until a goahead signal is received For many cells, the _____ checkpoint seems to be the most important If a cell receives a go-ahead signal at the G1 checkpoint, it will usually _____________________ the S, G2, and M phases and divide If the cell does not receive the go-ahead signal, it will exit the cycle, switching into a nondividing state called the ______________ phase The Cell Cycle Clock: Cyclins and Cyclin-Dedpendent Kinases Two types of regulatory proteins are involved in cell cycle control: Cdks activity fluctuates during the cell cycle because it is ______________________ by cyclins, so named because their concentrations vary with the cell cycle Stop and Go Signs: Internal and External Signals at the Checkpoints An example of an internal signal is that _______________________________ not attached to spindle microtubules send a molecular signal that delays anaphase Some external signals are ___________________________, proteins released by certain cells that stimulate other cells to ________________________ For example, platelet-derived growth factor (PDGF) stimulates the division of human fibroblast cells in culture A clear example of external signals is _____________________________________________, in which crowded cells stop dividing Most animal cells also exhibit _______________________________, in which they must be attached to a substratum in order to divide Cancer cells exhibit ________________ density-dependent inhibition nor anchorage dependence Loss of Cell Cycle Controls in Cancer Cells _____________________ cells do not respond normally to the body’s control mechanisms Cancer cells may not need growth factors to grow and divide They may make their own __________________________ They may convey a growth factor’s signal ______________ the presence of the growth factor They may have an ________________________ cell cycle control system A normal cell is converted to a cancerous cell by a process called ________________________ Cancer cells that are not eliminated by the immune system, form tumors, masses of abnormal cells within otherwise normal tissue If abnormal cells remain at the original site, the lump is called a ____________________ tumor _____________________________ tumors invade surrounding tissues and can ________________________, exporting cancer cells to other parts of the body, where they may form additional tumors Why does sexual reproduction require 2 parents and how does it promote genetic diversity? Variations on a Theme Living organisms are distinguished by their ability to reproduce their own kind Genetics is the scientific study of Heredity is the Variation is demonstrated by the differences in appearance that offspring Offspring Acquire Genes From Parents by Inheriting Chromosomes In a literal sense, children do not inherit particular ____________________ traits from their parents It is __________________ that are actually inherited What are Genes? Inheritance of Genes Genes are Genes are passed to the next generation via reproductive cells called _____________________ (sperm and eggs) Gametes are considered ____________________________________ cells because they only have one complete set of chromosomes Each gene has a specific location called a __________________ on a certain chromosome Sets of Chromosomes in Human Cells Human ______________________ cells (any cell other than a gamete) have 23 pairs of chromosomes How many total chromosomes? We refer these cells as being __________________________ cells Cell with ________________ sets of chromosomes A ________________________ is an ordered display of the pairs of chromosomes from a cell The two chromosomes in each pair are called ____________________________ chromosomes, or __________________________ Chromosomes in a homologous pair are the same ________________ and __________________ and carry __________________ controlling the same inherited characters The __________ chromosomes, which determine the sex of the individual, are called X and Y What are female’s sex chromosome combination? What are male’s sex chromosome combination? The remaining 22 pairs of chromosomes are called _____________________________ Now lets talk about sexual reproduction in Humans Behavior of Chromosome Sets in the Human Life Cycle At sexual maturity, the ________________ and __________________ produce haploid gametes Gametes are the only types of human cells produced by __________________, rather than mitosis Meiosis results in __________________ set of chromosomes in each ____________________ Why do the gametes have to be haploid? _____________________________ is the union of gametes The fertilized egg is called a ________________________ and has one set of chromosomes from each ________________________________ The zygote produces somatic cells by _________________ and develops into an _____________ How do we make haploid gametes? Meiosis Reduces the Number of Chromosome Sets From __________________ to _________________ Meiosis Like mitosis, is preceded by chromosome __________________________ Unlike mitosis, cell divides _______________ to form __________ haploid daughter cells The Stages of Meiosis After chromosomes duplicate, two divisions follow Meiosis I (reductional division): Meiosis II (equational division) The result is _____________ haploid daughter cells with ___________________ chromosomes Meiosis I In __________________________, homologous chromosomes are ______________ In ______________________________, homologous chromosomes __________________ corresponding segments Each homologous pair divides into ______ daughter cells, each with one set of chromosomes consisting of two ____________________________ Meiosis II Essentially the same as ____________________ Sister chromatids of each chromosome ___________________________ Result is _________ cells, each with ____________ as many chromosomes as the parent A Comparison of Mitosis and Meiosis Mitosis produces cells that are ______________________ identical to the parent cell Meiosis reduces the number of chromosomes sets from two (diploid) to one (haploid), producing cells that differ ____________________ from each other and from the parent cell Three events are unique to meiosis, and all three occur in meiosis l __________________________ and ____________________________ in prophase I: Homologous chromosomes physically __________________ and __________________ genetic information At the metaphase plate, there are paired homologous chromosomes (________________), instead of individual replicated chromosomes At anaphase I, it is _________________________ chromosomes, instead of sister chromatids, that separate How do we get genetic diversity? Genetic Variation Produced in Sexual Life Cycles Contributes to Evolution ____________________________ (changes in an organism’s DNA) are the original source of genetic diversity Mutations create different versions of genes called _________________ _____________________________ of alleles during sexual reproduction produces genetic variation Origins of Genetic Variation Among Offspring The behavior of chromosomes during meiosis and fertilization is responsible for most of the variation that arises in each generation Three mechanisms contribute to genetic variation Independent Assortment of Chromosomes Homologous pairs of chromosomes orient _______________________ at metaphase I of meiosis In ________________________ assortment, each pair of chromosomes sorts maternal and paternal homologues into daughter cells independently of the other pairs The number of combinations possible when chromosomes assort independently into gametes is 2n, where n is the ___________________ number For humans (n = 23), there are more than 8 million (223) possible combinations of chromosomes Crossing Over Crossing over produces _______________________ chromosomes, which combine DNA inherited from each parent In crossing over, homologous portions of two ____________________ chromatids trade places Crossing over contributes to genetic variation by __________________ DNA from two parents into a ______________________ chromosome Random Fertilization Random fertilization ________ to genetic variation because any sperm can fuse with any ovum (unfertilized egg) The fusion of two gametes (each with 8.4 million possible chromosome combinations from independent assortment) produces a zygote with any of about 70 trillion diploid combinations Crossing over adds even more variation Each zygote has a unique genetic identity Alterations of Chromosome Number or Structure Cause Some Genetic Disorders Large-scale chromosomal alterations in humans and other mammals often lead to spontaneous _____________________ (miscarriages) or cause a variety of developmental disorders Plants tolerate such genetic changes better than animals do Abnormal Chromosome Number In ________________________, pairs of homologous chromosomes do not separate normally during meiosis As a result, one gamete receives two of the same type of chromosome, and another gamete receives _____ copy _____________________________ results from the fertilization of gametes in which nondisjunction occurred Offspring with this condition have an abnormal _______________ of a particular chromosome A ________________________ zygote has only one copy of a particular chromosome A ________________________ zygote has three copies of a particular chromosome Down Syndrome (Trisomy 21) Down syndrome is an _____________________ condition that results from three copies of chromosome ______ It affects about one out of every 700 children born in the United States The frequency of Down syndrome increases with the ______ of the mother, a correlation that has not been explained Aneuploidy of Sex Chromosomes _________________________ of sex chromosomes produces a variety of aneuploid conditions _____________________________ syndrome is the result of an extra chromosome in a male, producing ______________ individuals Monosomy X, called _________________ syndrome, produces ______ females, who are sterile; it is the only known viable monosomy in humans __________________________ is a condition in which an organism has more than two complete sets of chromosomes _______________________ (3n) is three sets of chromosomes _______________________ (4n) is four sets of chromosomes Polyploidy is common in ________________, but not ____________________ Polyploids are more normal in appearance than _________________________ Alterations of Chromosome Structure Breakage of a chromosome can lead to four types of changes in chromosome structure _________________________ removes a chromosomal segment _________________________ repeats a segment _________________________ reverses orientation of a segment within a chromosome _________________________ moves a segment from one chromosome to another How are traits/characteristics passed on to future generations? The science of genetics has ancient roots Early attempts to explain heredity have been rejected by later science Hippocrates' theory of _____________________________ Particles from each part of the body travel to eggs or sperm and are passed on Early 19th-century biologists' _________________ hypothesis Traits from both parents __________ in the offspring Ex. If you cross a black and a brown lab you will get all black but then the next generation they will get a mixture of brown and black Experimental genetics began in an abbey garden ____________________________________ hypothesized that there are alternative forms of genes, the units that determine heritable traits Mendel crossed _____________________ plants that differed in certain characteristics Terminology of Mendelian genetics ______________________________: fertilization of eggs by sperm-carrying pollen of the same flower ______________________________: (cross): fertilization of one plant by pollen from a different plant ______________________________:: identical offspring from self-fertilizing parents ______________________________:: offspring of two different varieties ______________________________:: true-breeding parents ______________________________:: hybrid offspring of true-breeding parents ______________________________:: offspring of self-fertilizing F1 parents The ____________ characteristic Mendel followed in his studies Mendel's law of _________________________ describes the inheritance of a single characteristic From his experimental data, Mendel developed several hypotheses There are alternative forms (_________________) of genes that account for variation in inherited characteristics If the two alleles of an inherited pair differ The ______________________ allele determines the organism's appearance Ex. Purple flower (___) The ______________________ allele has no noticeable effect on the organism's appearance Ex. White flower (___) For each characteristic, an organism inherits two alleles, one from each parent __________________________: two __________________ alleles Homozygous dominant (____) Homozygouse recessive (____) __________________________: two ____________________ alleles Pp The law of segregation: The best way to understand the law of segregation is to know how to complete a ___________________ If you know an individuals phenotype do you automatically know it’s genotype? An organism's appearance does not always reveal its genetic composition __________________________: Genetic makeup __________________________: Expressed (physical) traits How do we figure out an unknown genotype? The ___________________ How can we tell the genotype of an individual with the dominant phenotype? Such an individual could be either ___________________ dominant or __________________ The answer is to carry out a _________________: breeding the mystery individual with a homozygous _______________________ individual If any offspring display the recessive phenotype, the mystery parent must be heterozygous The law of independent assortment is revealed by tracking two characteristics at once Mendel's law of independent assortment: The Laws of Probability Govern Mendelian Inheritance Mendel’s laws of ____________________ and ________________________________ reflect the rules of probability When tossing a coin, the outcome of one toss has no impact on the outcome of the next toss In the same way, the alleles of one gene segregate into gametes independently of another gene’s alleles How do you calculate probabilities when dealing with just one gene? How do you calculate probabilities when dealing with multiple genes? Variations of Mendel’s Laws Incomplete dominance results in intermediate phenotypes Complete dominance Incomplete dominance Many genes have more than two alleles in the population In a population, _____________________ alleles often exist for a single characteristic Example: human _____________ blood group Involves three alleles of a single gene AB blood group is an example of ________________________________-both alleles are expressed in heterozygotes A single gene may affect many phenotypic characteristics Pleiotropy: Example: sickle cell disease Why is sickle cell disease common among people of African descent? Epistasis In epistasis, For example, in Labrador retrievers and many other mammals, coat color depends on two genes One gene determines the pigment color (with alleles B for black and b for brown) The other gene (with alleles C for color and c for no color) determines whether the pigment will be deposited in the hair A single characteristic may be influenced by many genes Polygenic inheritance is Example: human skin color Controlled by at least __________________ genes The environment affects many characteristics Many characteristics result from a combination of genetic and environmental factors _______________ vs. ____________________ is an old and hotly contested debate Only genetic influences are inherited Ex. Heart disease, intellegence, body weight hydrangea flowers of the same genotype range from blue-violet to pink, depending on soil acidity Genes on the same chromosome tend to be inherited together ________________________ genes Lie ___________________ together on the same ___________________________ Tend to be _____________________________ together Generally do ____________ follow Mendel's law of independent assortment How Linkage Affects Inheritance Morgan did other experiments with __________________ to see how linkage affects inheritance of two characters Morgan crossed flies that differed in traits of body color and wing size Morgan found that body color and wing size are usually inherited together in specific ___________________________ (parental phenotypes) He noted that these genes do not ___________________ independently, and reasoned that they were on the same chromosome However, nonparental phenotypes were also produced when you had linked genes Understanding this result involves exploring ___________________________________ (crossing over), the production of offspring with combinations of traits differing from either parent For example Genetic Recombination and Linkage The genetic findings of Mendel and Morgan relate to the chromosomal basis of recombination and the chromosomal basis of inheritance Recombination of Unlinked Gene: Independent Assortment of Chromosomes Mendel observed that combinations of traits in some offspring differ from either parent Offspring with a phenotype matching one of the parental phenotypes are called Offspring with nonparental phenotypes (new combinations of traits) are called What is a Genetic Disorder? Genetic traits in humans can be tracked through family __________________________ The inheritance of many human traits follows ______________________ laws What would the genotype be or an individual if they exhibited a dominant disorder? What would the genotype be or an individual if they exhibited a recessive disorder? Pedigree Analysis A _________________________ is a family tree that describes the interrelationships of parents and children across generations Inheritance patterns of particular traits can be ____________ and __________________ using pedigrees Many inherited disorders in humans are controlled by a ________________ gene Thousands of human genetic disorders follow simple Mendelian patterns of inheritance __________________________ disorders _________________________ genetic disorders Can be carried unnoticed by __________________________ ? The Behavior of Recessive Alleles Recessively inherited disorders show up only in individuals ______________________ for the allele __________________________ are heterozygous individuals who carry the recessive allele but are phenotypically normal; most individuals with recessive disorders are born to carrier parents _____________________ is a recessive condition characterized by a lack of pigmentation in skin and hair If a recessive allele that causes a disease is __________, then the chance of two carriers meeting and mating is _________________ ____________________________ matings (i.e., matings between close relatives) _________________ the chance of mating between two carriers of the same rare allele Most societies and cultures have laws or taboos against marriages between close relatives ________________________ disorders Some serious, but ____________________, disorders (achondroplasia) Lethal conditions ____________________ common than in recessive disorders Cannot be carried by _________________________ without affecting the ? Multifactorial Disorders Many diseases, such as heart disease, diabetes, alcoholism, mental illnesses, and cancer have both genetic and environmental components Little is understood about the genetic contribution to most multifactorial diseases Genetic Testing and Counseling Genetic __________________ can provide information to prospective parents concerned about a family history for a specific disease Counseling Based on Mendelian Genetics and Probability Rules Using family histories, genetic counselors help couples determine the _______ that their children will have genetic disorders Probabilities are predicted on the most accurate information at the time; predicted probabilities may change as new information is available Tests for Identifying Carriers For a growing number of diseases, tests are available that identify carriers and help define the odds more accurately Fetal Testing In ___________________________, the liquid that bathes the fetus is removed and tested In ______________________________ (CVS), a sample of the placenta is removed and tested Other techniques, such as __________________ and __________________, allow fetal health to be assessed visually in __________ Newborn Screening Some genetic disorders can be detected at _____________ by simple tests that are now routinely performed in most hospitals in the United States The Chromosomal Basis of Inheritance Mendelian Inheritance has its Physical Basis in the Behavior of Chromosomes Mitosis and meiosis were first described in the late 1800s The _________________________________________________ states: Mendelian genes have specific ___________ (positions) on chromosomes Chromosomes undergo ___________________ and independent _____________________ The behavior of chromosomes during _______________________ can account for Mendel’s laws of segregation and independent assortment Sex-Linked Genes Exhibit Unique Patterns of Inheritance In humans and some other animals, there is a chromosomal basis of ________ determination Many animals have a pair of chromosomes that determine sex Humans: ___________ system Male is ______; the ___ chromosome has genes for the development of testes Female is _____; absence of a ___ chromosome allows ovaries to develop A gene that is located on either sex chromosome is called a ________________________ gene Genes on the Y chromosome are called __________________ genes; there are few of these Genes on the X chromosome are called __________________ genes Most sex-linked disorder are _____________________ disorders Inheritance of X-Linked Disorders X-linked disorders are typically ___________________________ disorders For a recessive X-linked trait to be expressed A female needs two copies of the allele (___________________________) A male needs only one copy of the allele (_____________________________) X-linked recessive disorders are much more common in ___________________ than in females Some disorders caused by recessive alleles on the X chromosome in humans ___________________________ (mostly X-linked) ___________________________ X Inactivation in Female Mammals In mammalian females, one of the two ____ chromosomes in each cell is randomly ________________ during embryonic development The inactive X condenses into a ____________________________ If a female is heterozygous for a particular gene located on the X chromosome, she will be a _________________________ for that character