Genetics SL Flashcards

Question

What. is a karyogram

Answer 1

The chromosomes are stained and photographed to generate a visual profile that is known as a karyogram The chromosomes of an organism are arranged into homologous pairs according to size

Answer 2

Down syndrome is a condition whereby the individual has three copies of chromosome 21 (i.e. trisomy 21) It is caused by a non-disjunction event in one of the parental gametes The extra genetic material causes mental and physical delays in the way the child develops One of the parental gametes had two copies of chromosome 21 as a result of non-disjunction The other parental gamete was normal and had a single copy of chromosome 21 When the two gametes fused during fertilisation, the resulting zygote had three copies of chromosome 21

Answer 3

Karyotyping will typically occur prenatally and is used to: Determine the gender of the unborn child (via identification of the sex chromosomes) Test for chromosomal abnormalities (e.g. aneuploidies or translocations)

Answer 4

Measuring the length of DNA molecule 1.Cells are grown in a solution containing radioactive thymidine (tritiated thymidine – 3H-T) 2.Thymidine is incorporated into the chromosomal DNA of the cell, 3.The chromosomes are isolated by gently lysing the cells and fixing the chromosomes to a photographic surface 4.The surface is then immersed in a radioactively-sensitive emulsion containing silver bromide (AgBr) 5.The radiation released from the tritiated thymidine converts the Ag+ ions in silver bromide into insoluble metal grains 6.Excess silver bromide is washed away, leaving the silver grains to appear as small black dots 7.When the photographic film is developed, the chromosomal DNA can be visualised with an electron microscope

Answer 5

Chromosome number is a characteristic feature of members of a particular species Organisms with different diploid numbers are unlikely to be able to interbreed (cannot form homologous pairs in zygotes) In cases where different species do interbreed, offspring are usually infertile (cannot form functional gametes)

Answer 6

Meiosis is the process by which sex cells (gametes) are made in the reproductive organs It involves the reduction division of a diploid germline cell into four genetically distinct haploid nuclei

Answer 7

Meiosis I The first meiotic division is a reduction division (diploid → haploid) in which homologous chromosomes are separated P-I: Chromosomes condense, nuclear membrane dissolves, homologous chromosomes form bivalents, crossing over occurs M-I: Spindle fibres from opposing centrosomes connect to bivalents (at centromeres) and align them along the middle of the cell A-I: Spindle fibres contract and split the bivalent, homologous chromosomes move to opposite poles of the cell T-I: Chromosomes decondense, nuclear membrane may reform, cell divides (cytokinesis) to form two haploid daughter cells Meiosis II The second division separates sister chromatids (these chromatids may not be identical due to crossing over in prophase I) P-II: Chromosomes condense, nuclear membrane dissolves, centrosomes move to opposite poles (perpendicular to before) M-II: Spindle fibres from opposing centrosomes attach to chromosomes (at centromere) and align them along the cell equator A-II: Spindle fibres contract and separate the sister chromatids, chromatids (now called chromosomes) move to opposite poles T-II: Chromosomes decondense, nuclear membrane reforms, cells divide (cytokinesis) to form four haploid daughter cells The final outcome of meiosis is the production of four haploid daughter cells

Answer 8

During Interphase DNA is replicated (in the S phase) to produce two genetically identical copies The two identical DNA molecules are identified as sister chromatids, and are held together by a single centromere The sister chromatids are separated during meiosis II, following the separation of homologous chromosomes in meiosis I

Answer 9

In prophase I, homologous chromosomes undergo a process called synapsis, whereby they pair up to form a bivalent (or tetrad) The homologous chromosomes are held together at points called chiasmata (singular: chiasma) Crossing over of genetic material between non-sister chromatids can occur at these chiasmata As a result of this exchange of genetic material, new gene combinations are formed on chromatids (recombination) Once chiasmata are formed, the homologous chromosomes condense as bivalents and then are separated in meiosis If crossing over occurs then all four haploid daughter cells will be genetically distinct (sister chromatids are no longer identical)

Answer 10

During metaphase I, homologous chromosomes line up at the equator as bivalents in one of two arrangements: Maternal copy left / paternal copy right OR paternal copy left / maternal copy right The orientation of pairs of homologous chromosomes is random, as is the subsequent assortment of chromosomes into gametes The final gametes will differ depending on whether they got the maternal or paternal copy of a chromosome following anaphase I As this random assortment will occur for each homologous pair, the number of possible gamete combinations are dependent on the number of homologous pairs Gamete combinations = 2n (where n represents the haploid number)

Answer 11

In order to reproduce, organisms need to make gametes that are haploid (one copy of each chromosome) Fertilisation of two haploid gametes (egg + sperm) will result in the formation of a diploid zygote that can grow via mitosis If chromosome number was not halved in gametes, total chromosome numbers would double each generation (polyploidy)

Answer 12

The three main sources of genetic variation arising from sexual reproduction are: Crossing over (in prophase I) Random assortment of chromosomes (in metaphase I) Random fusion of gametes from different parents

Answer 13

Non-disjunction refers to the chromosomes failing to separate correctly, resulting in gametes with one extra, or one missing, chromosome (aneuploidy)

Answer 14

Failure of homologues to separate in Anaphase I (resulting in four affected daughter cells) Failure of sister chromatids to separate in Anaphase II (resulting in only two daughter cells being affected)

Answer 15

Studies show that the chances of non-disjunction increase as the age of the parents increase The risk of chromosomal abnormalities in offspring increase significantly after a maternal age of 30 There is a higher incidence of chromosomal errors in offspring as a result of non-disjunction in meiosis I

Answer 16

Chorionic villi sampling involves removing a sample of the chorionic villus (placental tissue) via a tube inserted through the cervix It can be done at ~11 weeks of pregnancy with a slight risk of inducing miscarriage (~1%)

Answer 17

Amniocentesis involves the extraction of a small amount of amniotic fluid (contains fetal cells) with a needle It is usually conducted later than CVS (~16 weeks of pregnancy) with a slightly lower risk of miscarriage (~0.5%)

Answer 18

First, he crossed different varieties of purebred pea plants, then collected and grew the seeds to determine their characteristics Next, he crossed the offspring with each other (self-fertilization) and grew their seeds to similarly determine their characteristics These crosses were performed many times to establish reliable data trends (over 5,000 crosses were performed) As a result of these experiments, Mendel discovered the following things: When he crossed two different purebred varieties together the results were not a blend – only one feature would be expressed E.g. When purebred tall and short pea plants were crossed, all offspring developed into tall growing plants When Mendel self-fertilised the offspring, the resulting progeny expressed the two different traits in a ratio of ~ 3:1 E.g. When the tall growing progeny were crossed, tall and short pea plants were produced in a ratio of ~ 3:1

Answer 19

-Organisms have discrete factors that determine its features (these ‘factors’ are now recognised as genes) -Furthermore, organisms possess two versions of each factor (these ‘versions’ are now recognised as alleles) -Each gamete contains only one version of each factor (sex cells are now recognised to be haploid) -Parents contribute equally to the inheritance of offspring as a result of the fusion between randomly selected egg and sperm -For each factor, one version is dominant over another and will be completely expressed if present

Answer 20

When gametes form, alleles are separated so that each gamete carries only one allele for each gene

Answer 21

The segregation of alleles for one gene occurs independently to that of any other gene, however, this does not hold true for genes located on the same chromosome

Answer 22

Recessive alleles will be masked by dominant alleles, but some genes show co-dominance or incomplete dominance

Answer 23

During meiosis I, homologous chromosomes are separated into different nuclei prior to cell division As homologous chromosomes carry the same genes, segregation of the chromosomes also separates the allele pairs Consequently, as gametes contain only one copy of each chromosome they therefore carry only one allele of each gene

Answer 24

If the maternal and paternal alleles are the same

Answer 25

If the maternal and paternal alleles are different

Answer 26

Males only have one allele for each gene located on a sex chromosome and are said to be hemizygous for that gene

Answer 27

The gene composition (i.e. allele combination) for a specific trait is referred to as the genotype

Answer 28

The observable characteristics of a specific trait (i.e. the physical expression) is referred to as the phenotype

Answer 29

The phenotype is determined by both the genotype and environmental influences

Answer 30

Co-dominance occurs when pairs of alleles are both expressed equally in the phenotype of a heterozygous individual Heterozygotes therefore have an altered phenotype as the alleles are having a joint effect

Answer 31

Human red blood cells can be categorised into different blood groups based on the structure of a surface glycoprotein (antigen)

Answer 32

The A and B alleles are co-dominant and each modify the structure of the antigen to produce different variants The O allele is recessive and does not modify the basic antigenic structure

Answer 33

As humans produce antibodies against foreign antigens, blood transfusions are not compatible between certain blood groups AB blood groups can receive blood from any other type (as they already possess both antigenic variants on their cells) A blood groups cannot receive B blood or AB blood (as the isoantigen produced by the B allele is foreign) B blood groups cannot receive A blood or AB blood (as the isoantigen produced by the A allele is foreign) O blood groups can only receive transfusions from other O blood donor (both antigenic variants are foreign)

Answer 34

Surface antigens would interact with antibodies resulting in agglutination (blood clumping) and then hemolysis (destruction of RBC)

Answer 35

An autosomal recessive genetic disease will only occur if both alleles are faulty

Answer 36

An autosomal recessive genetic disease will only occur if both alleles are faulty Heterozygous individuals will possess one copy of the faulty allele but not develop disease symptoms (they are carriers

Answer 37

An autosomal dominant genetic disease only requires one copy of a faulty allele to cause the disorder

Answer 38

If a genetic disease is caused by co-dominant alleles it will also only require one copy of the faulty allele to occur However, heterozygous individuals will have milder symptoms due to the moderating influence of a normal allele

Answer 39

-Cystic fibrosis is an autosomal recessive disorder caused by a mutation to the CFTR gene on chromosome 7 -Individuals with cystic fibrosis produce mucus which is unusually thick and sticky -This mucus clogs the airways and secretory ducts of the digestive system, leading to respiratory failure and pancreatic cysts -Heterozygous carriers who possess one normal allele will not develop disease symptoms

Answer 40

-Huntington’s disease is an autosomal dominant disorder caused by a mutation to the Huntingtin (HTT) gene on chromosome 4 -The HTT gene possesses a repeating trinucleotide sequence (CAG) that is usually present in low amounts (10 – 25 repeats) -More than 28 CAG repeats is unstable and causes the sequence to amplify (produce even more repeats) -When the number of repeats exceeds ~40, the huntingtin protein will misfold and cause neurodegeneration -This usually occurs in late adulthood and so symptoms usually develop noticeably in a person’s middle age (~40 years) -Symptoms of Huntington’s disease include uncontrollable, spasmodic movements (chorea) and dementia

Answer 41

Alleles that adversely affects survival and hence the capacity to reproduce is unlikely to be passed on to offspring Recessive conditions tend to be more common, as the faulty allele can be present in carriers without causing disease Dominant conditions may often have a late onset, as this does not prevent reproduction and the transfer of the faulty allele

Answer 42

Sex linkage refers to when a gene controlling a characteristic is located on a sex chromosome (X or Y)

Answer 43

The Y chromosome is much shorter than the X chromosome and contains only a few genes (50 million bp; 78 genes) The X chromosome is longer and contains many genes not present on the Y chromosomes (153 million bp ; ~ 2,000 genes) Hence, sex-linked conditions are usually X-linked - as very few genes exist on the shorter Y chromosome

Answer 44

Human males have only one X chromosome (and therefore only one allele) and are hemizygous for X-linked traits X-linked recessive traits are more common in males, as the condition cannot be masked by a second all

Answer 45

Haemophilia is a genetic disorder whereby the body’s ability to control blood clotting (and hence stop bleeding) is impaired The formation of a blood clot is controlled by a cascade of coagulation factors whose genes are located on the X chromosome When one of these factors becomes defective, fibrin formation is prevented - meaning bleeding continues for a long time Different forms of haemophilia can occur, based on which specific coagulation factor is mutated (e.g. haemophilia A = factor VIII)

Answer 46

Red-Green Colour Blindness Red-green colour blindness is a genetic disorder whereby an individual fails to discriminate between red and green hues This condition is caused by a mutation to the red or green retinal photoreceptors, which are located on the X chromosome Red-green colour blindness can be diagnosed using the Ishihara colour test

Answer 47

A gene mutation is a change to the base sequence of a gene that can affect the structure and function of the protein it encodes

Answer 48

Mutations can be spontaneous (caused by copying errors during DNA replication) or induced by exposure to external elements

Answer 49

Radiation – e.g. UV radiation from the sun, gamma radiation from radioisotopes, X-rays from medical equipment Chemical – e.g. reactive oxygen species (found in pollutants), alkylating agents (found in cigarettes) Biological Agents – e.g. bacteria (such as Helicobacter pylori), viruses (such as human papilloma virus)

Answer 50

Agents which increase the rate of genetic mutations are called mutagens, and can lead to the formation of genetic disease

Answer 51

Mutagens which lead to the formation of cancer are more specifically referred to as carcinogens

Answer 52

A pedigree is a chart of the genetic history of a family over several generations Males are represented as squares, while females are represented as circles Shaded symbols mean an individual is affected by a condition, while an unshaded symbol means they are unaffected A horizontal line between man and woman represents mating and resulting children are shown as offshoots to this line Generations are labeled with roman numerals and individuals are numbered according to age (oldest on the left)

Answer 53

The polymerase chain reaction (PCR) is an artificial method of replicating DNA under laboratory conditions The PCR technique is used to amplify large quantities of a specific sequence of DNA from an initial minute sample Each reaction cycle doubles the amount of DNA – a standard PCR sequence of 30 cycles creates over 1 billion copies (230)

Answer 54

PCR occurs in a thermal cycler and uses variations in temperature to control the replication process via three steps: 1.Denaturation – DNA sample is heated to separate it into two single strands (~95ºC for 1 min) 2.Annealing – DNA primers attach to the 3’ ends of the target sequence (~55ºC for 1 min) 3.Elongation – A heat-tolerant DNA polymerase (Taq) binds to the primer and copies the strand (~72ºC for 2 min) Once large quantities of DNA have been created, other laboratory techniques are used to isolate and manipulate the sequences

Answer 55

DNA Separation -DNA may be cut into fragments using restriction endonuclease – different DNA samples will generate different fragment lengths -Fragments separate because DNA is negatively charged due to the presence of a phosphate group (PO43–) on each nucleotide -DNA samples are placed into an agarose gel and fragment size calculated by comparing against known industry standards -Specific sequences can be identified by incorporating a complementary radiolabelled hybridisation probe, transferring the separated sequences to a membrane and then visualising via autoradiography (Southern blotting)

Answer 56

Protein Separation -Proteins may be folded into a variety of shapes (affecting size) and have positive and negative regions (no clear charge) -Proteins must first be treated with an anionic detergent (SDS) in order to linearise and impart a uniform negative charge -Protein samples are placed into a polyacrylamide gel and sizes compared against known industry standards -Separated proteins are transferred to a membrane and then target proteins are identified by staining with specific monoclonal antibodies (Western blotting)

Answer 57

Samples are placed in a block of gel and an electric current is applied which causes the samples to move through the gel Smaller samples are less impeded by the gel matrix and hence will move faster through the gel This causes samples of different sizes to separate as they travel at different speeds

Answer 58

Within the non-coding regions of an individual’s genome there exists satellite DNA – long stretches of DNA made up of repeating elements called short tandem repeats (STRs) As individuals will likely have different numbers of repeats at a given satellite DNA locus, they will generate unique DNA profiles. Thus through a comparison we can DNA profile

Answer 59

Suspects should be a complete match with the DNA sample taken from the crime scene if a conviction is to occur The number of loci used to generate a unique profile depends on the size of the population being compare

Answer 60

Children inherit half their chromosomes from each parent and thus should possess a combination of parental fragments In other words, all fragments produced in the child should also be produced by either the mother or father

Answer 61

A gene determines a particular trait by encoding for a specific polypeptide in a given organism

Answer 62

Because the genetic code is (almost) universal, an organism can potentially express a new trait if the appropriate gene is introduced into its genome The transfer of genes between species is called gene modification, and the new organism created is called a transgenic

Answer 63

1.Isolation of gene and vector (by PCR) 2.Digestion of gene and vector (by restriction endonuclease) 3.Ligation of gene and vector (by DNA ligase) 4.Selection and expression of transgenic construct

Answer 64

Step 1: Isolating gene and vector DNA can be isolated from cells by centrifugation – whereby heavier components such as nuclei are separated The gene of interest can then be specifically amplified via the polymerase chain reaction (PCR) Gene sequences can also be generated from mRNA using reverse transcriptase – these DNA sequences (cDNA) lack introns A vector is a DNA molecule that is used as a vehicle to carry the gene of interest into a foreign cell Bacterial plasmids are commonly used as vectors because they are capable of autonomous self-replication and expression These plasmids may be modified for further functionality (e.g. selection markers, reporter genes, inducible expression promoters) Other types of vectors include modified viruses and artificial chromosomes

Answer 65

Step 2: Digestion with Restriction Enzymes In order to incorporate a gene of interest into a vector, both must be cut with restriction enzymes at specific recognition sites Restriction enzymes cleave the sugar-phosphate backbone to generate blunt ends or sticky ends (complementary overhangs) Scientists will often cleave the vector and gene with two different ‘sticky end’ restriction endonucleases (double digestion) to ensure the gene is inserted in the correct orientation and to prevent the vector from re-annealing without the desired insert

Answer 66

Step 3: Ligation of Vector and Insert The gene of interest is inserted into a plasmid vector that has been cut with the same restriction endonucleases This occurs because the sticky ends of the gene and vector overlap via complementary base pairing The gene and vector are then spliced together by the enzyme DNA ligase to form a recombinant construct DNA ligase joins the vector and gene by fusing their sugar-phosphate backbones together with a covalent phosphodiester bond

Answer 67

Step 4: Selection and Expression The recombinant construct (including the gene of interest) is finally introduced into an appropriate host cell or organism This process can be achieved in a variety of ways and is called transfection (for eukaryotes) or transformation (for prokaryotes) Antibiotic selection is commonly used in order to identify which cells have successfully incorporated the recombinant construct The plasmid vector contains an antibiotic resistance gene, so only transgenic cells will grow in the presence of antibiotic Transgenic cells, once isolated and purified, will hopefully begin expressing the desired trait encoded by the gene of interest

Answer 68

-grow in a wider range of environments (e.g. drought / frost / salinity resistance) -produce greater yields -genes which slow the rate of spoiling, leading to longer shelf lives for GM foods -may possess resistance to certain viruses or produce toxins to pests (reducing need for the use of pesticides)

Answer 69

-potentially reduce biodiversity in a region by competing with indigenous plant life -proteins or toxins produced by GM crops could negatively affect certain organisms within the ecosystem -formation of herbicide-resistant weeds and grasses

Answer 70

Clones are groups of genetically identical organisms or a group of cells derived from a single original parent cell

Answer 71

-Stem cells can be artificially generated from adult tissue using a process called somatic cell nuclear transfer (SCNT) -Organisms that reproduce asexually will produce genetically identical clones

Answer 72

Somatic cell nuclear transfer is a method by which cloned embryos can be produced using differentiated adult cells Somatic cells are removed from the adult donor and cultured (these cells are diploid and contain the entire genome) An unfertilised egg is removed from a female adult and its haploid nucleus is removed to produce an enucleated egg cell The enucleated egg cell is fused with the nucleus from the adult donor to make a diploid egg cell (with the donor’s DNA) An electric current is then delivered to stimulate the egg to divide and develop into an embryo The embryo is then implanted into the uterus of a surrogate and will develop into a genetic clone of the adult donor

Answer 73

-vegetative propagation -Binary fission -Budding -Fragmentation --Pathogenesis

Answer 74

The parent organism divides equally in two, so as to produce two genetically identical daughter organisms

Answer 75

Cells split off the parent organism, generating a smaller daughter organism which eventually separates from the parent

Answer 76

New organisms grow from a separated fragment of the parent organism

Answer 77

Embryos are formed from unfertilised ova (via the production of a diploid egg cells by the female)

Answer 78

Plants have the capacity for vegetative propagation, whereby small pieces can be induced to grow independently This is because adult plants possess meristematic tissue capable of cellular differentiation (totipotent)

Answer 79

Identical twins (monozygotic) are created when a fertilised egg (zygote) splits into two identical cells, each forming an embryo Non-identical twins (dizygotic) are created when an unfertilised egg splits into two cells and each is fertilised by a different sperm Identical twins will be clones of one another (genetically identical), while non-identical twins will share 50% of the same DNA

Answer 80

At a very early stage, embryonic cells retain pluripotency (meaning they can divide and become any type of tissue) These cells will differentiate to form all the different tissues comprising the organism If these embryonic cells are separated artificially in the laboratory, each group of cells will form cloned organisms This separation of embryonic cells can also occur naturally to give rise to identical (monozygotic) twins The separated groups of cells are then implanted into the uterus of a surrogate to develop into genetically identical clones

Answer 81

Reproductive cloning: If the embryo is implanted into the uterus of a surrogate, a new cloned organism will develop

Answer 82

Therapeutic cloning: Embryonic cells can be induced to differentiate to create specific tissues or organs for transplantation

Answer 83

This involves replacing the haploid nucleus of an unfertilised egg with a diploid nucleus from an adult donor The advantage of this technique is that it is known what traits the clones will develop (they are genetically identical to the donor)

Answer 84

Bacterial cells may exchange plasmids via their sex pili, in a process known as bacterial conjugation This exchange of genetic material allows bacteria to evolve new features within a generation

Answer 85

Prokaryotic DNA: Is found freely in the cytoplasm (within a region called the nucleoid) Is naked (i.e. not bound with proteins and therefore doesn’t form chromatin) Genomes are compact (contain little repetitive DNA and no introns) Contains extra-chromosomal plasmids Is circular in shape Eukaryotic DNA: Is contained within a nucleus Is bound to histone proteins Genomes contain large amounts of non-coding and repetitive DNA (including introns) Do not contain plasmids (but organelles such as the mitochondria may contain their own chromosomes) Are linear in shape

Answer 86

Homologous chromosomes are held together at points called chiasmata (singular: chiasma)

Answer 87

Similarities: They are both preceded by interphase (which includes DNA replication) They both divide according to a common pathway (prophase → metaphase → anaphase → telophase) They both split their cells via cytokinesis Differences: Division – Mitosis involves only one cell division, but meiosis requires two cell divisions Independent assortment – Homologous pairs are randomly separated into separate cells in meiosis, but not mitosis Synapsis – Homologous pairs form bivalents in meiosis, but not mitosis Crossing over – Non-sister chromatids of homologous pairs may exchange genetic material in meiosis, but not mitosis Outcome – Mitosis results in the formation of two daughter cells, while meiosis produces four daughter cells Ploidy – Daughter cells produced by mitosis are diploid, while daughter cells produced by meiosis are haploid Use – Mitosis is used to clone body cells, while meiosis is used to generate sex cells (gametes) Genetics – Cells produced by mitosis are genetically identical (clones), while cells produced by meiosis are genetically distinct Mnemonic: Disco Pug

Answer 88

It is possible to infer whether two genes are linked or unlinked by looking at the frequency distribution of potential phenotypes Offspring with unlinked genes have an equal possibility of inheriting any potential phenotypic combination This is due to the random segregation of alleles via independent assortment Offspring with linked genes will only express the phenotypic combinations present in either parent unless crossing over occurs Consequently, the ‘unlinked’ recombinant phenotypes occur less frequently than the ‘linked’ parental phenotypes A CHI-SQUARED test is required for statistical sagnificance

Answer 89

Monogenic traits (characteristics controlled by a single gene loci) tend to exhibit discrete variation, with individuals expressing one of a number of distinct phenotypes Polygenic traits (characteristics controlled by more than two gene loci) tend to exhibit continuous variation, with an individual’s phenotype existing somewhere along a continuous spectrum of potential phenotypes In the case of polygenic inheritance: Increasing the number of loci responsible for a particular trait increases the number of possible phenotypes This results in a phenotypic distribution that follows a Gaussian (bell-shaped) normal distribution curve

Answer 90

Stabalising Directional Disruptive

Answer 91

Temporal Isolation Temporal isolation occurs when two populations differ in their periods of activity or reproductive cycles Example: Leopard frogs and wood frogs reach sexual maturity at different times in the spring and hence cannot interbreed Behavioural Isolation Behavioural isolation occurs when two populations exhibit different specific courtship patterns Example: Certain populations of crickets may be morphologically identical but only respond to specific mating songs Geographic Isolation Geographic isolation occurs when two populations occupy different habitats or separate niches within a common region Example: Lions and tigers occupy different habitats and do not interbreed (usually)

Answer 92

Allopatric Speciation Allopatric speciation occurs when a geographical barrier physically isolates populations of an ancestral species The two populations begin to evolve separately as a result of cumulative mutation, genetic drift and natural selection Eventually the two populations reach a degree of genetic divergence whereby they can no longer interbreed (speciation) Sympatric Speciation Sympatric speciation is divergence of species within the same geographical location (i.e. without a physical barrier) Sympatric speciation may result from the reproductive isolation of two populations as a result of genetic abnormalities Typically, a chromosomal error may arise which prevents successful reproduction with any organism lacking the same error

Answer 93

Fertile polyploid offspring require two polyploid parents (unless allopolyploidy occurs) This is because reproduction with the original parent population results in offspring with an uneven number of chromosome sets Consequently, polyploidy is far more common in plant species as they may lack separate sexes (self polination) or can reproduce asexually (vegative propagation) Polyploid crops may be particularly desirable to farmers for a number of reasons: -Allows for the production of seedless fruits as the polyploid are infertile -Polyploid crops will typically grow larger and demonstrate improved longevity and disease resistance Consequently, farmers may induce polyploidy in certain plant species by treating plants with certain drugs

Answer 94

Phyletic Gradualism (Linear) Punctuated Equilibrium (Steps)