1. Chapter 14 Mendel and the Gene Idea

2. The “ blending ” hypothesis is the idea that genetic material from the two parents blends together (like blue and yellow paint blend to make green) Copyright © 2008 Pearson Education Inc., publishing as Pearson Benjamin Cummings

3. Mating two contrasting, true-breeding varieties, is called hybridization True-breeding parents are the P generation Hybrid offspring of the P generation are called the F 1 generation When F 1 individuals self-pollinate, the F 2 generation is produced Copyright © 2008 Pearson Education Inc., publishing as Pearson Benjamin Cummings Mendel used the scientific approach to identify two laws of inheritance

4. The Law of Segregation When Mendel crossed contrasting, true- breeding white and purple flowered pea plants, all of the F 1 hybrids were purple When Mendel crossed the F 1 hybrids, many of the F 2 plants had purple flowers, but some had white Mendel discovered a ratio of about three to one (3:1), purple to white flowers, in the F 2 generation Copyright © 2008 Pearson Education Inc., publishing as Pearson Benjamin Cummings

5. Fig. 14-3-3 EXPERIMENT P Generation (true-breeding parents) Purple flowers White flowers  F 1 Generation (hybrids) All plants had purple flowers F 2 Generation 705 purple-flowered plants 224 white-flowered plants

6.  alternative versions (alleles) of genes account for variations in inherited characters and are located at a specific locus on a specific chromosome (H,h) Copyright © 2008 Pearson Education Inc., publishing as Pearson Benjamin Cummings First concept:

7. Second concept: for each character an organism inherits two alleles, one from each parent the two alleles at a locus on a chromosome may be identical, as in the true-breeding or the two alleles at a locus may differ

8. Fig. 14-4 Allele for purple flowers Homologous pair of chromosomes Locus for flower-color gene Allele for white flowers

9. - if the two alleles at a locus differ, then one (the dominant allele) determines the organism ’ s appearance, and the other (the recessive allele) has no noticeable effect on appearance Copyright © 2008 Pearson Education Inc., publishing as Pearson Benjamin Cummings Third concept:

10. The fourth concept: law of segregation, states that the two alleles for a heritable character separate (segregate) during gamete formation and end up in different gametes an egg or a sperm gets only one of the two alleles that are present in the somatic cells of an organism (meiosis)

11. Fig. 14-5-3 P Generation Appearance: Genetic makeup: Gametes: Purple flowers White flowers PP P pp p F 1 Generation Gametes: Genetic makeup: Appearance: Purple flowers Pp P p 1/21/2 1/21/2 F 2 Generation Sperm Eggs P P PPPp p p pp 31

12. Useful Genetic Vocabulary Homozygous: organism with two identical alleles for a character Heterozygous: an organism that has two different alleles for a gene Phenotype, or physical appearance, Genotype, or genetic makeup Copyright © 2008 Pearson Education Inc., publishing as Pearson Benjamin Cummings

13. Fig. 14-6 Phenotype Purple 3 Genotype 1 White Ratio 3:1 (homozygous) (heterozygous) PP Pp pp Ratio 1:2:1 1 1 2

14. The Testcross  How can we tell the genotype of an individual with the dominant phenotype?  Carry out a testcross: breeding the mystery individual with a homozygous recessive individual  If any offspring display the recessive phenotype, the mystery parent must be heterozygous Copyright © 2008 Pearson Education Inc., publishing as Pearson Benjamin Cummings

15. Fig. 14-7 TECHNIQUE RESULTS Dominant phenotype, unknown genotype: PP or Pp? Predictions Recessive phenotype, known genotype: pp  If PPIf Pp or Sperm ppp p P P P p Eggs Pp pp or All offspring purple 1 / 2 offspring purple and 1 / 2 offspring white

16. The Law of Independent Assortment  Mendel derived the law of segregation by following a single character  The F 1 offspring produced in this cross were monohybrids, heterozygous for one character  Mendel identified his second law of inheritance by following two characters at the same time  Crossing two true-breeding parents differing in two characters produces dihybrids in the F 1 generation, heterozygous for both characters Copyright © 2008 Pearson Education Inc., publishing as Pearson Benjamin Cummings

17. Fig. 14-8 EXPERIMENT RESULTS P Generation F 1 Generation Predictions Gametes Hypothesis of dependent assortment YYRRyyrr YR yr YyRr  Hypothesis of independent assortment or Predicted offspring of F 2 generation Sperm YR yr Yr YR yR Yr yR yr YR YYRR YyRr YYRr YyRR YYrr Yyrr yyRR yyRr yyrr Phenotypic ratio 3:1 Eggs Phenotypic ratio 9:3:3:1 1/21/2 1/21/2 1/21/2 1/21/2 1/41/4 yr 1/41/4 1/41/4 1/41/4 1/41/4 1/41/4 1/41/4 1/41/4 1/41/4 3/43/4 9 / 16 3 / 16 1 / 16 Phenotypic ratio approximately 9:3:3:1 31510810132

18. What is the phenotypic ratio of a monohybrid cross? 3:1 What is the genotypic ratio of a monohybrid cross? 1:2:1 What is the phenotypic ratio of a dihybrid cross? 9:3:3:1

19. Extending Mendelian Genetics for a Single Gene  Inheritance of characters by a single gene may deviate from simple Mendelian patterns in the following situations: When alleles are not completely dominant or recessive When a gene has more than two alleles When a gene produces multiple phenotypes Copyright © 2008 Pearson Education Inc., publishing as Pearson Benjamin Cummings

20. Degrees of Dominance  Complete dominance occurs when phenotypes of the heterozygote and dominant homozygote are identical (purple, white)  In incomplete dominance, the phenotype of F 1 hybrids is somewhere between the phenotypes of the two parental varieties (red, white, pink)  In codominance, two dominant alleles affect the phenotype in separate, distinguishable ways (both colors are seen) Copyright © 2008 Pearson Education Inc., publishing as Pearson Benjamin Cummings

21. Multiple Alleles  Most genes exist in populations in more than two allelic forms  The four phenotypes of the ABO blood group in humans are determined by three alleles for the enzyme (I) that attaches A or B carbohydrates to red blood cells: I A, I B, and i.  I A I A or I A i, I B I B or I B i, ii Copyright © 2008 Pearson Education Inc., publishing as Pearson Benjamin Cummings

22. Pedigree Analysis  A pedigree is a family tree that describes the interrelationships of parents and children across generations  Inheritance patterns of particular traits can be traced and described using pedigrees Copyright © 2008 Pearson Education Inc., publishing as Pearson Benjamin Cummings

23. Fig. 14-15a Key Male Female Affected male Affected female Mating Offspring, in birth order (first-born on left)

24. Fig. 14-15b 1st generation (grandparents) 2nd generation (parents, aunts, and uncles) 3rd generation (two sisters) Widow’s peakNo widow’s peak (a) Is a widow’s peak a dominant or recessive trait? Wwww Ww ww Ww wwWW Ww or

25. The Behavior of Recessive Alleles  Recessively inherited disorders show up only in individuals homozygous for the allele  Carriers are heterozygous individuals who carry the recessive allele but are phenotypically normal (i.e., pigmented)  Albinism and sickle cell Copyright © 2008 Pearson Education Inc., publishing as Pearson Benjamin Cummings

26. Fig. 14-16 Parents Normal Sperm Eggs Normal (carrier) Normal (carrier) Albino Aa A A AA Aa a aa a 

27. Dominantly Inherited Disorders  Some human disorders are caused by dominant alleles  Dominant alleles that cause a lethal disease are rare and arise by mutation  Achondroplasia is a form of dwarfism caused by a rare dominant allele Copyright © 2008 Pearson Education Inc., publishing as Pearson Benjamin Cummings

28. Fig. 14-17 Eggs Parents Dwarf Normal Dwarf Sperm Dd  dd d D Dd dd Dd d d

29. Fig. 14-UN2 Degree of dominance Complete dominance of one allele Incomplete dominance of either allele Codominance Description Heterozygous phenotype same as that of homo- zygous dominant Heterozygous phenotype intermediate between the two homozygous phenotypes Heterozygotes: Both phenotypes expressed Multiple alleles Pleiotropy In the whole population, some genes have more than two alleles One gene is able to affect multiple phenotypic characters CRCRCRCR CRCWCRCW CWCWCWCW IAIBIAIB I A, I B, i ABO blood group alleles Sickle-cell disease PP Pp Example

30. If we were examining height, and we have an unknown male who is tall, how can we determine if he is homozygous or heterozygous for the tall gene? Practice Problem: