author unknown address unknown accessed unknown Meiosis Polygenic Inheritance Polygenic Inheritance Dihybrid X & Autosomal Linkage Dihybrid X & Autosomal Linkage

D. Sources of Variation D. Sources of Variation Mizzou, University of Missouri- Columbia accessed A. Meiosis A. Meiosis C. Crossing Over C. Crossing Over B. Independent Assortment B. Independent Assortment

A. Meiosis 1. Describe the behaviour of the chromosomes in the phases of meiosis_ University of Wisconsin Madison accessed

A. Meiosis 1. Describe the behaviour of the chromosomes in the phases of meiosis_ University of Wisconsin Madison accessed eapbiofield accessed eapbiofield accessed ClickPlay

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 accessed

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 accessed

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 accessed 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 accessed 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 accessed 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 2 23 ie. over 8 million combinations_ Deborah Crocker accessed

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 accessed

D. Recombination D. Recombination Nature Wallpaper Blog accessed A. Dihybrid Crosses A. Dihybrid Crosses C. Linked Genes C. Linked Genes B. Types of Chromosomes B. Types of Chromosomes

Play 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- RrYy_ author unknown address unknown accessed unknown

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

6. In this example the F 2 generation could consist of any the 16 possible combinations of gametes author unknown address unknown accessed unknown 1. FOR SEED COLOR ONLY, WHAT IS THE RATIO OF YELLOW TO GREEN SEEDS? 2. FOR SEED SHAPE ONLY, WHAT IS THE RATIO OF WRINKLED TO ROUND SEEDS? 3. ALTHOUGH THERE ARE 16 COMBINATIONS OF FACTORS SHOWN, HOW MANY DIFFERENT APPEARANCES OF SEED ARE THERE? WHAT ARE THEY? 4. FOR THE DIFFERENT TYPES OF SEED APPEARANCE GIVEN IN (3), WORK OUT THE RATIO OF THERE DIFFERENT TYPES THAT WILL OCCUR IN THE F 2 GENERATION. 5. IF THE F 2 GENERATION PRODUCED 1712 SEEDS, HOW MANY SEEDS OF EACH APPEARANCE WOULD THERE B? 1. FOR SEED COLOR ONLY, WHAT IS THE RATIO OF YELLOW TO GREEN SEEDS? 2. FOR SEED SHAPE ONLY, WHAT IS THE RATIO OF WRINKLED TO ROUND SEEDS? 3. ALTHOUGH THERE ARE 16 COMBINATIONS OF FACTORS SHOWN, HOW MANY DIFFERENT APPEARANCES OF SEED ARE THERE? WHAT ARE THEY? 4. FOR THE DIFFERENT TYPES OF SEED APPEARANCE GIVEN IN (3), WORK OUT THE RATIO OF THERE DIFFERENT TYPES THAT WILL OCCUR IN THE F 2 GENERATION. 5. IF THE F 2 GENERATION PRODUCED 1712 SEEDS, HOW MANY SEEDS OF EACH APPEARANCE WOULD THERE B? Think about it! 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 accessed

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 accessed Think

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 accessed IN THE SWEET PEA (LATTHYRUS ODORATUS), A PURE-BREEDING PLANT WITH PURPLE FLOWERS AND LONG POLLEN GRAINS WAS CROSSED WITH A PURE- BREEDING PLANT HAVING RED FLOWERS AND SHORT POLLEN GRAINS. ALL THE F 1 OFFSPRING HAD PURPLE FLOWERS AND LONG POLLEN GRAINS. 1. WHICH ARE THE DOMINANT ALLELES? …THE RECESSIVE ALLELES? 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? IN THE SWEET PEA (LATTHYRUS ODORATUS), A PURE-BREEDING PLANT WITH PURPLE FLOWERS AND LONG POLLEN GRAINS WAS CROSSED WITH A PURE- BREEDING PLANT HAVING RED FLOWERS AND SHORT POLLEN GRAINS. ALL THE F 1 OFFSPRING HAD PURPLE FLOWERS AND LONG POLLEN GRAINS. 1. WHICH ARE THE DOMINANT ALLELES? …THE RECESSIVE ALLELES? 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? Think about it! Think

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 accessed THERE ARE SOME INTERESTING ASPECTS OF MENDEL’S WORK, INCLUDING THOSE MENTIONED IN 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 19TH CENTURY DOES OPERATE FOR THE MAJORITY OF PAIRS OF GENES. Theory of Knowledge TOKThink

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 TtBb b. in representing crosses involving linkage, it is more common to show them as vertical pairs, for example _ University of Alberta accessed Think

4. When doing crosses between two linked genes a. alleles are usually shown side-by-side in dihybrid crosses eg TtBb b. in representing crosses involving linkage, it is more common to show them as vertical pairs, for example _ University of Alberta accessed IN THE SWEET PEA (LATTHYRUS ODORATUS), A PURE-BREEDING PLANT WITH PURPLE FLOWERS AND LONG POLLEN GRAINS WAS CROSSED WITH A PURE- BREEDING PLANT HAVING RED FLOWERS AND SHORT POLLEN GRAINS. ALL THE F1 OFFSPRING HAD PURPLE FLOWERS AND LONG POLLEN GRAINS. THE GENES FOR FLOWER COLOR AND POLLEN GRAIN LENGTH ARE LINKED. 1. TRY CROSSING TWO OF THE OFFSPRING OF THE F 1 GENERATION AGAIN. 2. WHAT ARE THE PARENT GENOTYPES? …WHAT GAMETES DO THEY PRODUCE? 3. WHAT IS THE EXPECTED PHENOTYPIC RATIO? IN THE SWEET PEA (LATTHYRUS ODORATUS), A PURE-BREEDING PLANT WITH PURPLE FLOWERS AND LONG POLLEN GRAINS WAS CROSSED WITH A PURE- BREEDING PLANT HAVING RED FLOWERS AND SHORT POLLEN GRAINS. ALL THE F1 OFFSPRING HAD PURPLE FLOWERS AND LONG POLLEN GRAINS. THE GENES FOR FLOWER COLOR AND POLLEN GRAIN LENGTH ARE LINKED. 1. TRY CROSSING TWO OF THE OFFSPRING OF THE F 1 GENERATION AGAIN. 2. WHAT ARE THE PARENT GENOTYPES? …WHAT GAMETES DO THEY PRODUCE? 3. WHAT IS THE EXPECTED PHENOTYPIC RATIO? Think about it! 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 non- sister 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 accessed

author unknown address unknown accessed unknown A. Polygenic Inheritance A. Polygenic Inheritance B. Continuous Variation B. Continuous Variation

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

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 author unknown address unknown accessed unknown 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_ Lion Den accessed

B. Continuous Variation 1.Polygenic inheritance can contribute to continuous variation a. height and skin color in humans_ Lion Den accessed author unknown address unknown accessed unknown author unknown address unknown accessed unknown Click