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Chapter 14 Mendel and the Gene Idea

Chapter 14 Mendel and the Gene Idea. p 272 Ch 14 Genetics Problems (17) – due Nov. 4 p 291 Ch 15 Genetics Problems (14) - The answers are in the back of the book!!!! - I need to get the impression that you have worked out the problems & not copied the correct answer!!.

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Chapter 14 Mendel and the Gene Idea

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  1. Chapter 14 Mendel and the Gene Idea p 272 Ch 14 Genetics Problems (17) – due Nov. 4 p 291 Ch 15 Genetics Problems (14) - The answers are in the back of the book!!!! - I need to get the impression that you have worked out the problems & not copied the correct answer!!

  2. Chapter 14 Mendel and the Gene Idea Removed stamens from purple flower 1 APPLICATION By crossing (mating) two true-breeding varieties of an organism, scientists can study patterns of inheritance. In this example, Mendel crossed pea plants that varied in flower color. Transferred sperm- bearing pollen from stamens of white flower to egg- bearing carpel of purple flower 2 TECHNIQUE TECHNIQUE TECHNIQUE RESULTS Parental generation (P) Stamens (male) Carpel (female) Pollinated carpel matured into pod 3 Planted seeds from pod 4 When pollen from a white flower fertilizes eggs of a purple flower, the first-generation hybrids all have purple flowers. The result is the same for the reciprocal cross, the transfer of pollen from purple flowers to white flowers. Examined offspring: all purple flowers 5 First generation offspring (F1) • What do you know about genetics? • Mendel – Father of Genetics – peas P generation F1 Generation

  3. Chapter 14 Mendel and the Gene Idea P Generation (true-breeding parents)  EXPERIMENT True-breeding purple-flowered pea plants and white-flowered pea plants were crossed (symbolized by ). The resulting F1 hybrids were allowed to self-pollinate or were cross- pollinated with other F1 hybrids. Flower color was then observed in the F2 generation. Purple flowers White flowers F1 Generation (hybrids) All plants had purple flowers RESULTS Both purple-flowered plants and white- flowered plants appeared in the F2 generation. In Mendel’s experiment, 705 plants had purple flowers, and 224 had white flowers, a ratio of about 3 purple : 1 white. F2 Generation

  4. Chapter 14 Mendel and the Gene Idea Allele for purple flowers Homologous pair of chromosomes Locus for flower-color gene Allele for white flowers • What do you know about genetics? • Mendel – Father of Genetics – peas • Allele – alternate form of a gene that gives different traits • Dominant allele • gives a visible trait with only 1 copy • A • Recessive allele • gives a visible trait with 2 copies • a

  5. Chapter 14 Mendel and the Gene Idea • What do you know about genetics? • Mendel – Father of Genetics – peas • Allele – alternate form of a gene that gives different traits • Dominant allele • gives a visible trait with only 1 copy • A • Recessive allele • gives a visible trait with 2 copies • a • Homozygous • 2 copies of the same allele • AA or aa • Heterozygous • 1 copy of each allele • Aa • True breeders • parents who mate & always yield the same genetic offspring • AA x AA or aa x aa

  6. Chapter 14 Mendel and the Gene Idea • What do you know about genetics? • Mendel – Father of Genetics – peas • Allele – alternate form of a gene that gives different traits • Dominant allele • Recessive allele • Homozygous • Heterozygous • True breeders • parents who mate & always yield the same genetic offspring • AA x AA or aa x aa • Monohybrid – organism that’s heterozygous for 1 gene of interest • Dihybrid – organism that is heterozygous for 2 genes of interest • Genotype – genetic make up of an organism (its alleles) • Phenotype – physical traits exhibited – based on genotype

  7. Phenotype Genotype Purple PP (homozygous) 1 Pp (heterozygous) 3 Purple 2 Pp (heterozygous) Purple pp (homozygous) White 1 1 Ratio 3:1 Ratio 1:2:1 Figure 14.6 Phenotype versus genotype

  8. Test corrections • Staple corrections behind • Tuck scantron inside • Place in box • Can transport tomorrow – all day & 4:30

  9. Chapter 14 Mendel and the Gene Idea • What do you know about genetics? • Mendel – Father of Genetics – peas • Allele – alternate form of a gene that gives different traits • Dominant allele • Recessive allele • Homozygous • Heterozygous • True breeders • parents who mate & always yield the same genetic offspring • AA x AA or aa x aa • Monohybrid – organism that’s heterozygous for 1 gene of interest • Dihybrid – organism that is heterozygous for 2 genes of interest • Genotype – genetic make up of an organism (its alleles) • Phenotype – physical traits exhibited – based on genotype • Law of Segregation – each allele in a pair seegregates into a different gamete during gamete formation (Anaphase I)

  10. Each true-breeding plant of the parental generation has identical alleles, PP or pp. Gametes (circles) each contain only one allele for the flower-color gene. In this case, every gamete produced by one parent has the same allele. P Generation  Appearance:Genetic makeup: Purple flowerPP White flowerspp Gametes: p P Union of the parental gametes produces F1 hybrids having a Pp combination. Because the purple- flower allele is dominant, all these hybrids have purple flowers. When the hybrid plants produce gametes, the two alleles segregate, half the gametes receiving the P allele and the other half the p allele. F1 Generation Appearance:Genetic makeup: Purple flowersPp Gametes: Figure 14.5 Mendel’s law of segregation

  11. Each true-breeding plant of the parental generation has identical alleles, PP or pp. Gametes (circles) each contain only one allele for the flower-color gene. In this case, every gamete produced by one parent has the same allele. Each true-breeding plant of the parental generation has identical alleles, PP or pp. Gametes (circles) each contain only one allele for the flower-color gene. In this case, every gamete produced by one parent has the same allele. P Generation P Generation   Appearance:Genetic makeup: Appearance:Genetic makeup: Purple flowerPP Purple flowerPP White flowerspp White flowerspp Gametes: Gametes: p p P P Union of the parental gametes produces F1 hybrids having a Pp combination. Because the purple- flower allele is dominant, all these hybrids have purple flowers. When the hybrid plants produce gametes, the two alleles segregate, half the gametes receiving the P allele and the other half the p allele. Union of the parental gametes produces F1 hybrids having a Pp combination. Because the purple- flower allele is dominant, all these hybrids have purple flowers. When the hybrid plants produce gametes, the two alleles segregate, half the gametes receiving the P allele and the other half the p allele. F1 Generation F1 Generation Appearance:Genetic makeup: Appearance:Genetic makeup: Purple flowersPp Purple flowersPp Gametes: Gametes: 1/2 1/2 p P F1 sperm This box, a Punnett square, shows all possible combinations of alleles in offspring that result from an F1 F1 (PpPp) cross. Each square represents an equally probable product of fertilization. For example, the bottom left box shows the genetic combination resulting from a p egg fertilized by a P sperm. p P F2 Generation P Pp PP F1 eggs p pp Pp Random combination of the gametes results in the 3:1 ratio that Mendel observed in the F2 generation. 3 : 1 Figure 14.5 Mendel’s law of segregation

  12. Chapter 14 Mendel and the Gene Idea • What do you know about genetics? • Mendel – Father of Genetics – peas • Allele – alternate form of a gene that gives different traits • Dominant allele • Recessive allele • Homozygous • Heterozygous • True breeders • parents who mate & always yield the same genetic offspring • AA x AA or aa x aa • Monohybrid – organism that’s heterozygous for 1 gene of interest • Dihybrid – organism that is heterozygous for 2 genes of interest • Genotype – genetic make up of an organism (its alleles) • Phenotype – physical traits exhibited – based on genotype • Law of Segregation – each allele in a pair segregates into a different gamete during gamete formation (Anaphase I) • Testcross – breeding an organism of unknown genotype with a homozygous recessive

  13. Figure 14.7 The Testcross  Dominant phenotype, unknown genotype: PP or Pp? Recessive phenotype, known genotype: pp APPLICATION An organism that exhibits a dominant trait, such as purple flowers in pea plants, can be either homozygous forthe dominant allele or heterozygous. To determine the organism’s genotype, geneticists can perform a testcross. TECHNIQUE In a testcross, the individual with the unknown genotype is crossed with a homozygous individual expressing the recessive trait (white flowers in this example). By observing the phenotypes of the offspring resulting from this cross, we can deduce the genotype of the purple-flowered parent. If PP, then all offspring purple: If Pp, then 1⁄2 offspring purple and 1⁄2 offspring white: p p p p RESULTS P P Pp Pp Pp Pp P p Pp pp Pp pp

  14. Chapter 14 Mendel and the Gene Idea • What do you know about genetics? • Mendel – Father of Genetics – peas • Allele – alternate form of a gene that gives different traits • Dominant allele • Recessive allele • Homozygous • Heterozygous • True breeders • parents who mate & always yield the same genetic offspring • AA x AA or aa x aa • Monohybrid – organism that’s heterozygous for 1 gene of interest • Dihybrid – organism that is heterozygous for 2 genes of interest • Genotype – genetic make up of an organism (its alleles) • Phenotype – physical traits exhibited – based on genotype • Law of Segregation – each allele in a pair segregates into a different gamete during gamete formation (Anaphase I) • Testcross – breeding an organism of unknown genotype with a homozygous recessive • Law of Independent Assortment – each pair of alleles separates independently during gamete formation when genes for 2 traits are on different homologous chromosomes (Metaphase I)

  15. EXPERIMENT Two true-breeding pea plants—one with yellow-round seeds and the other with green-wrinkled seeds—were crossed, producing dihybrid F1 plants. Self-pollination of the F1 dihybrids, which are heterozygous for both characters, produced the F2 generation. The two hypotheses predict different phenotypic ratios. Note that yellow color (Y) and round shape (R) are dominant. P Generation YYRR yyrr Gametes YR yr  F1 Generation YyRr RESULTS Hypothesis of independent assortment Hypothesis of dependent assortment Sperm Yr 1 ⁄4 1 ⁄4 YR 1 ⁄4 yR yr 1 ⁄4 Sperm Eggs 1 ⁄2 yr 1 ⁄2 YR 1 ⁄4 YR Eggs YyRr YYRR YYRr YyRR 1 ⁄2 YR F2 Generation (predicted offspring) YYRR YyRr 1 ⁄4 Yr YYrr Yyrr YyRr YYRr yr 1 ⁄2 yyrr YyRr 1 ⁄4 yR YyRR YyRr yyRR yyRr 3 ⁄4 1 ⁄4 yr 1 ⁄4 Phenotypic ratio 3:1 Yyrr YyRr yyRr yyrr CONCLUSION The results support the hypothesis of independent assortment. The alleles for seed color and seed shape sort into gametes independently of each other. 1 ⁄16 3 ⁄16 3 ⁄16 9 ⁄16 Phenotypic ratio 9:3:3:1 108 315 101 Phenotypic ratio approximately 9:3:3:1 32 Figure 14.8 Do the alleles for seed color and seed shape sort into gametes dependently (together) or independently?

  16. Chapter 14 Mendel and the Gene Idea Rr Segregation of alleles into eggs Rr Segregation of alleles into sperm   Sperm r R 1⁄2 1⁄2 R R r R R 1⁄2 1⁄4 1⁄4 Eggs r r R r r 1⁄2 1⁄4 1⁄4 • What do you know about genetics? Terms to know… • How does genetics reflect probabilities? • 0 = never will happen • 1 = always happens • Consider a coin…. • Probability of heads = 0.5 • Probability of tails = 0.5 • What is the rule of multiplication? • prob. of RR offspring from • Rr x Rr • R (½ ) x R (½) = ¼ • Prob. of rr offspring from • Rr x Rr • r (½) x r (½) = ¼ • What is the rule of addition? • Prob. of Rr offspring from • Rr x Rr • R (½) x r (½) = ¼ (1st parent gives R) • R (½) x r (½) = ¼ (2nd parent gives R) • ¼ + ¼ = ½ Rr offspring • Only when Rr x Rr make Rr

  17. Let’s practice….. PpYyRr x Ppyyrr ½ · ½· ½ · 1 · ½ · 1 = 1/16 ½ · ½ · ½ · 1 · ½ · 1 = 1/16 (½ · ½) + (½ · ½) · ½ · 1 · ½ · 1 = ½ · ½ · 1 · ½ · 1 = 1/8 ½ · ½ · ½ · 1 · ½ · 1 = 1/16 ½ · ½ · ½ · 1 · ½ · 1 = 1/16 • ppyyRr = ? • ppYyrr = ? • Ppyyrr = ? • PPyyrr = ? • ppyyrr = ? 1/16 1/16 1/8 1/16 1/16

  18. Chapter 14 Mendel and the Gene Idea P Generation White CWCW Red CRCR  Gametes CR CW Pink CRCW F1 Generation 1⁄2 1⁄2 Gametes CR CR Sperm 1⁄2 1⁄2 CR CR Eggs F2 Generation 1⁄2 CR CR CR CR CW 1⁄2 Cw CR CW CW CW • What do you know about genetics? Terms to know… • How does genetics reflect probabilities? • What is the rule of multiplication? • What is the rule of addition? • What is incomplete dominance? • Heterozygous phenotype is in • between the 2 homozygous • phenotypes • snapdragons • 1:2:1 for phenotype = genotype

  19. Chapter 14 Mendel and the Gene Idea • What do you know about genetics? Terms to know… • How does genetics reflect probabilities? • What is the rule of multiplication? • What is the rule of addition? • What is incomplete dominance? • What is codominance? • Phenotype shows both alleles being expressed • Both alleles can be detected • Blood typing – glycoprotein on RBC • Blood typing also shows • multiple alleles (more than 2 • allelic variations at a gene locus)

  20. Chapter 14 Mendel and the Gene Idea Tay-Sachs disease – brain cells cannot metabolize a certain lipid because of an enzyme deficiency Phenotype seen - dd (homozygous recessive) - consider Dd - appear normal – 1 copy sufficient - biochemically – incomplete dominance – less enzyme activity can be detected….in between DD and dd - molecularly – codominant – both normal enzyme & mutant enzyme can be detected

  21. Chapter 14 Mendel and the Gene Idea • What do you know about genetics? Terms to know… • How does genetics reflect probabilities? • What is the rule of multiplication? • What is the rule of addition? • What is incomplete dominance? • What is codominance? • What is pleiotropy? • 1 gene with multiple effects • Sickle cell allele • RBC form a sickle shape (“C”) when oxygen deprived causing blood flow problems leading to fatigue, pain, brain damage, • What is epistasis? • - Gene at 1 locus alters the phenotypic expression of a gene at a 2nd locus

  22. BbCc BbCc  Sperm 1⁄4 bC 1⁄4 Bc 1⁄4 BC bc 1⁄4 Eggs 1⁄4 BBCC BbCC BbCc BC BBCc 1⁄4 bC BbCC bbCC bbCc BbCc 1⁄4 BBcc BBCc BbCc Bbcc Bc bbcc Bbcc BbCc 1⁄4 bbCc bc 4⁄16 9⁄16 3⁄16 Figure 14.11 An example of epistasis B = black coat b = brown coat C = pigment c = no pigment In order to have color, the cells must have pigment.

  23. Chapter 14 Mendel and the Gene Idea • What do you know about genetics? Terms to know… • How does genetics reflect probabilities? • What is the rule of multiplication? • What is the rule of addition? • What is incomplete dominance? • What is codominance? • What is pleiotropy? • What is epistasis? • What is polygenic inheritance? • An additive effect of 2 or more genes on a single phenotype • Opposite of pleiotropy • Skin pigmentation

  24. Figure 14.12 A simplified model for polygenic inheritance of skin color  AaBbCc AaBbCc aabbcc Aabbcc AABBCc AABBCC AaBbcc AaBbCc AABbCc 20⁄64 15⁄64 Fraction of progeny 6⁄64 1⁄64 Skin pigmentation controlled by 3 separate genes

  25. Chapter 14 Mendel and the Gene Idea • What do you know about genetics? Terms to know… • How does genetics reflect probabilities? • What is the rule of multiplication? • What is the rule of addition? • What is incomplete dominance? • What is codominance? • What is pleiotropy? • What is epistasis? • What is polygenic inheritance? • Can the environment influence phenotype? • Plants – leaf shape, size, greenness – depend on wind, sunlight, rain nutrition – Figure 50.9 • Us – height, weight, exercise – depend on nutrition - Hydrangea color depends on soil acidity - Multifactorial – many factors, genetic & environmental influence phenotype

  26. First generation (grandparents) ww ww Ww Ww Ff Ff ff Ff Second generation (parents plus aunts and uncles) ww Ww Ww ww Ww Ff ww ff Ff FF or Ff Ff ff Third generation (two sisters) ff FF or Ff WW or Ww ww No Widow’s peak Free earlobe Widow’s peak Attached earlobe (a) Dominant trait (widow’s peak) (b) Recessive trait (attached earlobe) Figure 14.14 Pedigree analysis Pedigree analysis - follows specific traits over generations of a family

  27. Chapter 14 Mendel and the Gene Idea • What do you know about genetics? Terms to know… • How does genetics reflect probabilities? • What is the rule of multiplication? • What is the rule of addition? • What is incomplete dominance? • What is codominance? • What is pleiotropy? • What is epistasis? • What is polygenic inheritance? • Can the environment influence phenotype? • What are some recessively inherited human disorders? • - Only seen as dd, Dd are considered carriers • Cystic fibrosis – caused by a defect in a Cl- channel protein in lungs which leads to a mucus build up because an increase in Cl- concentration • 1 in 2500 Caucasians of European descent • 1 in 25 (4%) carriers • Sickle-cell disease

  28. Chapter 14 Mendel and the Gene Idea • What do you know about genetics? Terms to know… • How does genetics reflect probabilities? • What is the rule of multiplication? • What is the rule of addition? • What is incomplete dominance? • What is codominance? • What is pleiotropy? • What is epistasis? • What is polygenic inheritance? • Can the environment influence phenotype? • What are some recessively inherited human disorders? • 12. What are some dominantly inherited alleles? • - Achondroplasia • - form of dwarfism • - 1 in 25,000 • - Huntington’s disease • - degenerative disease of the nervous system • - lethal dominant • - phenotype visible between 35 – 45 yrs old • - 1 in 10,000

  29. Chapter 14 Mendel and the Gene Idea • What do you know about genetics? Terms to know… • How does genetics reflect probabilities? • What is the rule of multiplication? • What is the rule of addition? • What is incomplete dominance? • What is codominance? • What is pleiotropy? • What is epistasis? • What is polygenic inheritance? • Can the environment influence phenotype? • What are some recessively inherited human disorders? • 12. What are some dominantly inherited alleles? • 13. How do doctors test for genetic anomalies? • - amniocentesis • - chorionic villus sampling (CVS)

  30. (b) Chorionic villus sampling (CVS) (a) Amniocentesis Amniotic fluid withdrawn A sample of chorionic villus tissue can be taken as early as the 8th to 10th week of pregnancy. A sample of amniotic fluid can be taken starting at the 14th to 16th week of pregnancy. Fetus Fetus Suction tube Inserted through cervix Centrifugation Placenta Chorionic viIIi Placenta Uterus Cervix Fluid Fetal cells Fetal cells Biochemical tests can be Performed immediately on the amniotic fluid or later on the cultured cells. Biochemical tests Karyotyping and biochemical tests can be performed on the fetal cells immediately, providing results within a day or so. Several weeks Several hours Fetal cells must be cultured for several weeks to obtain sufficient numbers for karyotyping. Karyotyping Figure 14.17 Testing a fetus for genetic disorders

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