Genetics Meiosis Dihybrid X Autosomal Linkage Polygenic Inheritance
Genetics Meiosis Dihybrid X & Autosomal Linkage Polygenic Inheritance author unknown address unknown accessed unknown
Meiosis A. Meiosis B. Independent Assortment C. Crossing Over D. Sources of Variation Mizzou, University of Missouri- Columbia http: //web. missouri. edu/~news/releases/birchlerchromosomepainting. html accessed 12 -03 -07
A. Meiosis 1. Describe the behaviour of the chromosomes in the phases of meiosis_ eapbiofield https: //eapbiofield. wikispaces. com/Ch+13+Meiosis+and+Sexual+Life+Cycles+ANP accessed 16. 04. 09 University of Wisconsin Madison http: //botit. botany. wisc. edu/images/130/Meiosis/Lilium_microsporogenesis/ accessed 10. 04. 08 Click Play
B. Independent Assortment 1. During the first division of meiosis (during metaphase I) chromosomes line up in pairs on the equator of the cell_ Science Prof Online http: //scienceprofonline. googlepages. com/celldivisionmitosisandmeiosis accessed 17. 05. 09
2. Although the chromosomes line up in homologous pairs it is: a. entirely random which way round the pairs line up b. entirely random which one of the pair (maternal or paternal) is pulled to which pole during anaphase I_ author unknown address unknown accessed unknown
3. Because of this ‘random orientation’ each daughter cell could be equally likely to receive: • either one of chromosome 1 • either one of chromosome 2 • either one of chromosome 3… • either one of chromosome 23_ author unknown address unknown accessed unknown
4. How many possibilities is this? • two possibilities for chromosome 1 • multiplied by two possibilities for chromosome 2…_ Alan Bauer Photography http: //www. alanbauer. com/Waterfowl. htm accessed 16. 04. 09
C. Crossing Over 1. During prophase I of meiosis a. chromatids of homologous chromosomes become tightly associated (synapsis) b. results in a combined pair of homologous chromosomes 1) bivalent- two homologous chromosomes 2) tetrad- four chromatids within the stucture_ University of Central Arkansas http: //faculty. uca. edu/~johnc/reprod 1440. htm accessed 23 -04 -07 Allott, Mindorff p. 131
2. The maternal and paternal chromosomes exchange corresponding sections o DNA a. new combinations of alleles will have been created once crossing over is complete b. recombination- the process by which offspring possess a combination of alleles different from that of either parent_ University of Central Arkansas http: //faculty. uca. edu/~johnc/reprod 1440. htm accessed 23 -04 -07 Allott, Mindorff p. 131
3. A chiasma is an X-shaped structure formed between non-sister chromatids during prophase I of meiosis a. the chiasma is a physical manifestation of crossing over b. usually between one and three chiasmata form per homologous pair c. the chiasmata persist through metaphase I and play a role in the prevention of nondisjunction_ RCN http: //users. rcn. com/jkimball. ma. ultranet/Biology. Pages/M/Meiosis. html accessed 10. 04. 08 Allott, Mindorff p. 131
D. Sources of Variation 1. Meiosis results in an effectively infinite genetic variety of gametes through: a crossing over in prophase I b. random orientation in metaphase I 1) which gives 223 ie. over 8 million combinations_ Deborah Crocker http: //deborahcrocker 5. blogspot. com/2008/02/chapter-11 -vocab. html accessed 16. 04. 09
2. In addition to meiosis, variation is caused by random fusion of gametes a. one of over 8 million possible sperm fuses with one of over 8 million possible eggs 3. The ultimate source of all variation is mutation of DNA_ USC, University of South Carolina http: //www. jour. sc. edu/pages/wigginsweb/life 2200501. html accessed 12 -0307
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Dihybrid X & Autosomal Linkage A. Dihybrid Crosses B. Types of Chromosomes C. Linked Genes D. Recombination Nature Wallpaper Blog http: //www. exterpassive. com/naturewallpapers/index. php/archives/331 accessed 20. 04. 08
A. Dihybrid Crosses 1. A dihybrid cross results from crossing organisms that differ in two characteristics a. seed color (Y- yellow and y - green) b. seed shape (R- round and r-wrinkled) 2. The P generation can each produce gametes of one type a. RY and ry respectively 3. A cross between parental gametes results in an F 1 generation that are hybrids for the two characteristics a. round/yellow- Rr. Yy_ author unknown address unknown accessed unknown Play
4. Each of the resulting offspring can produce any one of four types of gametes a. RY, Ry, Yr, ry 5. Crossing between two hybrids of the F 1 generation can produce any of 4 possible phyenotypes a. yellow round b. yellow wrinkled c. green round d. green wrinkled_ author unknown address unknown accessed unknown
6. In this example the F 2 generation could consist of any the 16 possible combinations of gametes a. 9 possible genotypes b. 4 possible phenotypes (9: 3: 3: 1 ratio)_ author unknown address unknown accessed unknown Think
B. Types of Chromosomes 1. Sex chromosomes determine the sex of a human a. called X and Y b. X and Y do not look alike c. do not carry all the genes responsible for development of sexual characteristics 2. All the other chromosomes are called autosomes a. homologous pairs look alike b. pairs are numbered 1 -22_ College of Saint Benedict and Saint John's University http: //employees. csbsju. edu/hjakubowski/classes/ch 331/dna/oldnastructure. html accessed 16. 04. 08
C. Linked Genes 1. Mendel found that a dihybrid cross between two hybrids for two usually produces a phenotypic ratio of 9: 3: 3: 1 a. independent assortment_ You Grow Girl http: //www. yougrowgirl. com/thedirt/2006/06/20/feed-them-to-the-squirrels/ accessed 07. 05. 08 Think
Think about it! C. Linked Genes IN THE SWEET PEA (LATTHYRUS ODORATUS), A PURE-BREEDING PLANT WITHfound PURPLE FLOWERS 1. Mendel that a dihybrid AND LONG POLLEN GRAINS WAS CROSSED WITH A PURE- BREEDING PLANT HAVING REDtwo hybrids cross between FLOWERS AND SHORT POLLEN GRAINS. ALL THE F 1 OFFSPRING HAD for. PURPLE two FLOWERS usually. AND produces a LONG POLLEN GRAINS. phenotypic ratio of 9: 3: 3: 1 1. WHICH ARE THE DOMINANT ALLELES? …THE RECESSIVE ALLELES? a. independent assortment_ 2. WHAT LETTERS (CASE) SHOULD BE USED TO REPRESENT THE ALLELES? 3. CROSS TWO OF THE OFFSPRING OF THE F 1 GENERATION. 4. WHAT ARE THE PARENT GENOTYPES? …WHAT GAMETES DO THEY PRODUCE? 5. WHAT IS THE EXPECTED PHENOTYPIC RATIO? You Grow Girl http: //www. yougrowgirl. com/thedirt/2006/06/20/feed-them-to-the-squirrels/ accessed 07. 05. 08 Think
Theory of Knowledge THERE ARE SOME INTERESTING ASPECTS OF MENDEL’S WORK, INCLUDING THOSE MENTIONED IN 4. 3. 11. THE LAW OF INDEPENDENT ASSORTMENT WAS SOON FOUND TO HAVE EXCEPTIONS, WHEN PAIRS OF GENES ARE LINKED ON A CHROMOSOME, BUT THE LAW THAT MENDEL DISCOVERED IN THE 19 TH CENTURY DOES OPERATE FOR THE MAJORITY OF PAIRS OF GENES. You Grow Girl http: //www. yougrowgirl. com/thedirt/2006/06/20/feed-them-to-the-squirrels/ accessed 07. 05. 08 C. Linked Genes 1. Mendel found that a dihybrid cross between two hybrids for two usually produces a phenotypic ratio of 9: 3: 3: 1 a. independent assortment_ Think TOK
2. Sometimes a dihybrid cross between two hybrids for two traits produces a phenotypic ratio of approximately 3: 1 a. phenotypes of Bateson and Punnett’s F 2 sweet peas b. observed ratios of different types lead to the discovery of linked genes b. certain characteristics are inherited together 3. Linkage group- a group of genes whose loci are on the same chromosome_ Michael Kent: Advanced Biology
4. When doing crosses between two linked genes a. alleles are usually shown side-by-side in dihybrid crosses eg Tt. Bb b. in representing crosses involving linkage, it is more common to show them as vertical pairs, for example _ University of Alberta http: //www. biology. ualberta. ca/courses. hp/bio 207. hp/lab/fly_lab. htm accessed 16 -03 -07 Think
5. The gene for flower color and the gene for pollen shape are linked a. this explains why most of the offspring in Bateson and Punnett’s experiment were paternal types_ Michael Kent: Advanced Biology
D. Recombination 1. The linkage between genes in a linkage group is usually not complete a. new combinations of alleles are sometimes formed b. a result of crossing over_
3. Crossing over between nonsister chromatids of a homologous pair in prophase I can result in an exchange of alleles 4. The formation of a new chromosome or DNA with a new combination of alleles is recombination_ Michael Kent: Advanced Biology
5. An organism that has this recombinant chromosome has a different combination of characteristics from either parent 6. In a dihybrid cross involving linked genes some of the offspring are recombinants: in a test cross of the recombinants will be and Stony Brook University http: //life. bio. sunysb. edu/ee/geeta/Plants. html accessed 07. 05. 08 _
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Polygenic Inheritance A. Polygenic Inheritance B. Continuous Variation author unknown address unknown accessed unknown
A. Polygenic Inheritance 1. Polygenic inheritance is when more than one gene affects a single trait a. produces a broad range of phenotypes_ author unknown address unknown accessed unknown Click
B. Continuous Variation 1. Polygenic inheritance can contribute to continuous variation a. height and skin color in humans_ author unknown address unknown accessed unknown Lion Den http: //www. lionden. com/ap 1 out-skin. htm accessed 14. 05. 08 Click
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