مراجعة هيكل امتحان الأحياء الصف 11 متقدم الفصل الثاني

مراجعة هيكل امتحان الأحياء الصف 11 متقدم الفصل الثاني

DNA Tools

You have learned that selective breeding is used to produce plants and animals with desired traits. Genetic engineering can be used to increase or decrease the expression ot spec-Itu- genes In selected isms It has many applrauons trom human health to agnculture

An organisms genome is the total DNA present an the nucleus oi each cell. As will learn in the next section. genomes. such as the human genome. can contam nullons and nullms ot nucleotides. In order to study a specific gene. DNA tools can be used to manipulate DNA and to isolate genes from the rest of the genome

Restriction enzymes Some types ot bateria powerful delenses ag.unst Viruses These cells contain proteins called restric

tion enzymes that recognize and bind to specific DNA sequences and cleave the DNA Within that sequence. A restriction enzyme. also called an endonuclease (en NEW kJee avn cuts the viral DNA into fragments after it enters the bactena. Since their discovery in the late 1%Os scientists have identified and isolated hundreds ot restric- tion enzymes Restriction enzymes are used as powerful tools tor latinticnes or regions ot the geno  When the restnction enzyme cleave genomic DNA. it creates fragments 01 ditterent sizes that are umque to every individual

Ecom One restncuon enzvme that is used widely by scientists iS known as EcoRL As illustrated in Figure 4. EcoRI specifically CUts DNA containing the sequence GAMIC, The ends of the DNA fragments created by EcoRl are called sucky ends because thev contain single stranded DNA that is complementary. The ability od some restriction enzymes to create fragments With sticky ends is important because these sticky ends can be K’ined together with other DNA fragments that have complementary sticky ends

Reading Check how restriction enzymes ore used

Recombinant DNA Technology

When DNA fragments have been vparated by gel electrtxresis. frag ments Size can be removed trom thc gel and ctM1btrwd With DNA tragrnents tnxn aryher senjrce This ruwlv generated DNA molecuk. With ONA frcun ditkrent VAIrces. is calkd recombinant DNA. Recombinant DNA technolmv has rewoluti  vien- tists stLÄiv DNA txcause it enables Indtvkual gerws to be Large quantities rewornbtnant DNA molecules are needed in order to studv them. A carrier. called a vector. transfers the recombi nant DNA into a bactenal cell called the host cell. mastnxls and Viruses are commonly used vectors Plasmids small. circular. double stranded DNA thar occur naturally in b.wtena yeast cells- can be used as vectors because thev can be cut With restriction enzymes It plasmid and a DNA fragment trom another genome have been cleaved by the same restriction enzvme. the ends ot each DNA fragment Will be complementary can be combined, as shown in 6. An enzvme normally used bv cells in OXA repatt and replication. called DNA ligase. iotns the two DNA trag ments chemical}v ioins DNA fragments that have sticky ends as well as those that have blunt ends Examine 6 again. Nonce that the resulting circular DNA molecule ccuitalns plasmid DNA and the DNA fragment isolated from another gen•mw. nus recombinant plasmid DNA rmiecule now can Inserted into a host cell that large quanuoes ot this  ot re«Nnbtrunt DNA can nude

Reading Check  restroon enzymes to recombnont DNA

A Gntists can jor DNA tingerpnnting NR is used to copv this small armxmt DNA to create a larger sample bor analysis ampltIRd DNA tlwn is cut different cvxnbtrutkns enzvrrws Iragnunts are separated by gel ehctrKTIxresis and compared to DNA tragrwnts such as Victims and susr«-ts in a cnnurul case, to krate sanular patterns Tlwre ts a tugh probability that the two DNA cany trocn tw same it two tragrnentatm patterns match Sance Its veloprnent in Englamd  DNA finger, Ntnting has tu•en used only to cnrrutuls also to tree innxent vxopk wtxt hat wrongfully trnprivqud 14 a closet at the history genetic technokigy Reding Check Summarin how fotensac soentrsts use DNA Identifying Genes Once the genome has been sequenced. the next step in the process is to ntlty the genes and deternune their turu- tjons. The tunct•ons ot manv ot the genes in the human genome are still unknown

Researchers use techmques that Integrate computer analvsts and recombinant DNA technology to determine the function these gerws For orgamsms such as bactena and yeast. wt»se genomes have large regicrrs turroding DNA. researchers have identified genes bv scanrung the sequence tor open reading frames (or ORES. pronounced ORFs are stretches ot DNA contajntng at least that With a start oxton and end With a stop c’kion While these sequences nught indicate a gene. they Will tested to determine it these sequences produce 

Patterns mtgratxM were critical to Darwin when was develop ing hts ttxory Migration patterns explained why. for exams. islands often have rmre plant diversity than arumal diversity tty plants are nue able to migrate trom closest mainland as seeds either by Wind on the bxks 01 birds. Since DarwtnS time. scientists have con firmed and Darwins stiÄtv ot the distribution ot plants arurnals around world in a fild study calkd biogeography Evolutj’l is inunutelv linked with climate and geokNraI lorces. espe
cullv tecta- ax-s. which helps exüln many am-estral in tossals IiVtng organisms tlXday Adaptation

The five discussed in prevxnjs section- the tossil record comparative anatomy. comparat ive embrvolmy. comparative bxchenv iStry and distnbuton otter evidence Ior evolutm. Darwjn drew on all these except baxhettustrv which was not well devel ovxd in his time to develop his own theorv ot evolution bv natural selecticn At the heart ot his thecry lies the curept ot adaptation

Types of adaptation An adaptation is a trait shaped bv natural selec that increases an organisms reproductive success Orr wav to ‘hterrmne ettecuveÄ’ a tran contributes to reproductive success is to measure fitness. Fitness is a ot the relatrve contribution that an tnd1WduaI tran makes to tip rwxt gerwraton It often is meac sured as the number ot reproductively Viable ottspnng that an organ tsm pnxttres  the rwxt generatxn The an orgamsrn iS adapted to Its environment. the greater its chances ot survtval and reprcxtuctrve success This concept explains the vanatms Darwin in finches beaks on the Galapagos Islatxis. Because the envircmments dittered on each island. dilleteru beak characteristics were selected LN

Camouflage Some species have evolved morphological that allow trptn to bieruf tn With thetr envtronnwnts. This called camouflage Camouflage allows orgarusms to becouw almost invisi bk to as stwwn in ‘I. As J result. more ot camow flaged tndtvduals survwe reprodwe,