Unit 7 Part 1: Mendelian Genetics Notes

Transcription

1 Uni 7 Par 1: Mendelian Geneics Noes We know ha geneic informaion is passed from paren o offspring, bu unil recenly, we didn know how. Gregor Mendel Mos of our undersanding of geneics comes from Gregor Mendel. Mendel was an Ausrian monk who ended he gardens in his monasery. He made observaions abou he pea plans in his garden, and his led o 8 years of sudy! He repored his findings in 1866, and he science of Geneics was born. (Geneics = he branch of science ha sudies herediy, or how rais are passed from generaion o generaion.) *** Keep in mind ha Mendel knew NOHING abou DNA or chromosomes as he was doing his experimens!!!*** Why peas? Can be grown in a small area Produce los of offspring quickly Can be arificially pollinaed Mendel used good experimenal design, carefully documened his resuls, and used mahemaical analysis o make his conclusions. He was able o demonsrae ha inheried characerisics are carried by separae unis ha will laer be called genes. Reasons for Success: Mendel sudied disconinuous rais, which don show a range. Canale LE Page 1

2 here were 7 differen rais ha Mendel sudied, and oday we know ha hey are carried on a differen pair of chromosomes. Each rai sudied had 2 forms ( all or shor, yellow or green, ec.) We now know ha rais are carried on genes, and differen forms of a gene are called alleles. Principle of Dominance When Mendel crossed pure all plans wih pure shor plans, he go hundreds of seeds ha only resembled ONE paren! Since he offspring received one allele from each paren, one allele mus be dominan over he oher. When crossing wo plans ha were pure for a cerain rai, he characerisic ha appeared in he offspring was he dominan rai. he one ha didn was he recessive. Ou of he 7 rais ha Mendel sudied all had one allele ha was dominan and one ha was recessive. Canale LE Page 2

3 Recessive Dominan o represen he differen alleles, Mendel used leers. Dominan alleles are represened by CAPIAL leers Recessive alleles are represened by lowercase leers Example: Alleles for heigh in pea plans: and Some rais will mask ohers. he dominan allele produces a funcional proein ha affecs he characerisic. he recessive allele produces a non-funcional proein ha has no noiceable effec. If boh alleles are he same, he organism is homozygous for ha rai (or pure ) Example: = pure all = pure shor Canale LE Page 3

4 If he alleles are differen, he organism is heerozygous for ha rai (or hybrid ) Example: = hybrid all = hybrid all Genoype and Phenoype he Genoype is he geneic makeup of an individual Homozygous dominan = Homozygous recessive = Heerozygous = he Phenoype: is he physical characerisic ha is observed, = all plans = shor plan Law of Segregaion: During gamee formaion, he wo genes responsible for each rai separae from each oher so ha each gamee conains only one gene for each rai. **here s a 50/50 chance of receiving eiher allele! Law of Dominance: If you cross wo homozygous individuals wih conrasing rais, here will be only one phenoype in he nex generaion he dominan rai! Canale LE Page 4

5 **Pollen ransferred from whie flower o sigma of purple flower Offspring were allowed o self - pollinae and he resuls were observed Raios: wo pure ( homozygous ) individuals will produce 100% hybrid ( heerozygous ) offspring. hese offspring will ALL show he dominan phenoype. wo hybrid ( heerozygous ) individuals will produce offspring wih a 3:1 raio of dominan o recessive phenoype. hey will produce a 1:2:1 genoype raio. 25 Beyond Mendel: No all rais are deermined by jus _one gene. Human eye color, skin color and heigh are examples of polygenic rais. Law of Independen Assormen: If he genes for wo differen rais are locaed on differen chromosomes, hey segregae randomly during meiosis and can be inheried independenly of each oher. Example: he genes for heigh and seed color in pea plans are no locaed on he same chromosome. Canale LE Page 5

6 Our opions: all or shor for heigh, yellow or green for seed color Offspring could be : all Yellow all Green Shor Yellow Shor Green he Punne Square Mehod Punne Squares are used o predic he genoypes and phenoypes of offspring, using a mahemaical raio. hey operae on he Laws of Probabiliy, which show he possible combinaions of alleles no he guaraneed offspring! Seps for Using Punne Squares: 1. Deermine genoypes o cross 2. Separae he alleles ino eggs and Sperm 3. Perform cross 4. Deermine he genoype and phenoype raios Cross a homozygous all plan wih a heerozygous all plan! homozygous all = heerozygous all = Sample problems: Wha raios can be expeced in he offspring of a cross beween he following: Hybrid all plan X Shor plan = all = Shor Canale LE Page 6

7 Genoype raio: Phenoype raio: 50% 50% 50% all 50% Shor Wha is he expeced raio of offspring produced in a cross beween: Hybrid all plan X Hybrid all plan = all = Shor Genoype raio: 25% 50% 25% Phenoype raio: 75% all 25% Shor Mendel found ha pure wrinkled seeded plans crossed wih pure round seeded plans resuled in 100% round-seeded plans. Dominan allele = round = R Recessive allele = wrinkled = r Pure wrinkled = rr Cross a pure wrinkled seeded plan wih a hybrid round plan. Hybrid round = Rr R r Canale LE Page 7 r Rr rr

8 Genoype raio: Phenoype raio: 50% RR 50% rr 50% round 50% wrinkled es Cross: You can deermine he phenoype of an organism, bu no is genoype. Cross ha organism wih a homozygous recessive organism! By looking a he phenoypes of he offspring, you can deduce he genoype of he paren organism. **Remember ha you need wo recessive genes o see he rai! Example: A farmer waned o know wheher he all pea plans on his farm were heerozygous or homozygous. Possible combinaions for all pea plans: or Recessive genes for shor plans: his is he es cross organism = pure recessive Canale LE Page 8

9 If all offspring are all, hen he paren mus have been homozygous all. If he raio of all:shor is 50/50, hen he paren mus have been heerozygous all. he Need for LARGE Numbers: As he number of rials increases, he observed raios are closer o hose prediced by he laws of chance. ranslaion: he expeced Mendelian raios are more likely o appear when MANY offspring are produced. ***Which will give you beer resuls doing somehing 10 imes or 1000 imes? Canale LE Page 9