1 / 26

Chapter 14

Chapter 14. Mendel and the Gene Idea. Gregor Mendel. Monk Pea Plants  many varieties, easy to reproduce and control, tracked traits that were “either-or”, started with true breeding plants. P Generation (true-breeding parents). . Purple flowers. White flowers. F 1 Generation

estevan-gutierrez
Download Presentation

Chapter 14

An Image/Link below is provided (as is) to download presentation Download Policy: Content on the Website is provided to you AS IS for your information and personal use and may not be sold / licensed / shared on other websites without getting consent from its author. Content is provided to you AS IS for your information and personal use only. Download presentation by click this link. While downloading, if for some reason you are not able to download a presentation, the publisher may have deleted the file from their server. During download, if you can't get a presentation, the file might be deleted by the publisher.

E N D

Presentation Transcript

  1. Chapter 14 Mendel and the Gene Idea

  2. Gregor Mendel Monk Pea Plants  many varieties, easy to reproduce and control, tracked traits that were “either-or”, started with true breeding plants

  3. P Generation (true-breeding parents)  Purple flowers White flowers F1 Generation (hybrids) All plants had purple flowers F2 Generation Experiments • P generation = true breeding parents • Purple x White • F1 generation = hybrids from P generation cross • All purple plants • F2 generation = offspring from F1 self-pollination • 3:1 ratio of purple to white plants

  4. Allele for purple flowers Homologous pair of chromosomes Locus for flower-color gene Allele for white flowers Figure 14.4 Mendel’s Conclusions • Alternate versions of genes • ALLELES • Found on Homologous Chromosomes • Represented with letters

  5. Each trait is controlled by 2 alleles – one contributed from each parent

  6. The Law of Segregation • The 2 alleles for a trait segregate during gamete formation (meiosis) and end up in different gametes

  7. Mendel’s Other Law: • The Law of Independent Assortment • Genes located on different chromosomes are inherited independently • Exceptions: genes far away on same chromosome (many map units apart) allowing crossing over to occur can be inherited independently • * Genes located close together and are usually inherited together are called “linked” ex: red hair, freckles

  8. Some alleles are dominant while others are recessive • Dominant alleles “mask” recessive • Dominant alleles = capital letters • Recessive alleles = lowercase letters

  9. Vocab • Homozygous = 2 of the same alleles • Homozygous Dominant = DD • Shows dominant trait • Homozygous Recessive = dd • Shows recessive trait • Heterozygous = 1 dominant, 1 recessive allele • Heterozygous = Dd • Shows dominant trait and masks recessive • Genotype = allele make up (ex: DD) • Phenotype = physical trait

  10. Determine Probabilities • Punnett Squares • Aka Monohybrid Cross  1 trait • Explains Law of Segregation

  11. Testcross • Allows us to determine the genotype of an organism with the dominant phenotype, but unknown genotype • Is the organism DD or Dd?! • Crosses an individual with the dominant phenotype with an individual that is homozygous recessive for a trait

  12. 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 • The testcross Figure 14.7

  13. Dihybrid Cross Typical Outcome for 2 heterozygous individuals: 9:3:3:1 • Shows inheritance of two traits • Ex: seed color AND seed shape

  14. Types of Dominance • Complete Dominance • Phenotype of Dd is the same as DD • Codominance • Shows 2 dominant traits • Ex: BB = black, WW = white, BW = black AND white • Incomplete Dominance • Shows blended pattern • Ex: CRCR = Red, CwCw = White, CRCW = Pink

  15. Codominance vs. Incomplete Dominance

  16. Table 14.2 Multiple Alleles • Most traits are controlled by 2 alleles (ex: DD) • Some traits have more than 2 alleles • ABO Blood Type • IA, IB, i are the 3 alelles

  17. Pleiotropy • 1 gene has multiple phenotypic effects • Ex: Sickle Cell Anemia

  18. AaBbCc AaBbCc aabbcc Aabbcc AABBCc AABBCC AaBbcc AaBbCc AABbCc 20⁄64 15⁄64 Fraction of progeny 6⁄64 1⁄64 Multiple Genes (Polygenic) Ex: Hair, Skin, Eye Color Additive Effects

  19. Epistasis Outcome differs from 9:3:3:1 • A gene at one locus alters the phenotypic expression of a gene at a second locus (masks the other gene) • Ex: Laborador Retrievers • 2 genes: (E,e) & (B,b) • pigment (E) or no pigment (e) • pigment concentration: black (B) to brown(b)

  20. Multifactorial Traits Controlled by genetics and environment Ex: Skin color in humans, hydrangea color Nature vs. Nurture

  21. Pedigrees Circles = Females Squares = Males Shaded = Expresses phenotype Half-Shaded = Carriers Parents joined by horizontal lines Offspring listed below parents in birth order

  22. Human Genetic Disorders • Most are recessive (require homozygous recessive genotype) • Carriers = heterozygous individuals that do not show trait, but “carry” the gene for it (Ex: Aa) • Cystic Fibrosis: defective chloride channel in cell membranes lead to build up of thickened mucus • Tay-Sach’s disease: brain cells cannot metabolize lipids • Sickle-Cell Anemia: misshaped blood cells

  23. Human Genetic Disorders • Huntington’s Disease: Dominant, degenerative disease of nervous system • Achondroplasia: Dominant form of dwarfism (“AA” is lethal) • Many disorders are multifactorial • Heart disease • Cancer • Diabetes

  24. Carrier Recognition • Fetal Testing • Amniocentesis: withdrawl of fluid from amniotic sac to collect cells for viewing and karyotyping • Chorionic villus sampling (CVS): small amount of tissue suctioned from placenta • Ultrasound: non-invasive, reveals structures • Newborn Screening • Blood: test for PKU (Phenylketonuria) • Recessive disorder that leads to mental retardation • Requires a change in diet

More Related