Any heavy metal ion (such as copper cations in copper sulfate) can act as a noncompetitive inhibitor of catalase

1. Any heavy metal ion (such as copper cations in copper sulfate) can act as a noncompetitive inhibitor of catalase Hemophilia is an X-linked recessive disorder characterized by the inability to properly form blood clots.Victoria's son Prince Leopold, Duke of Albany suffered from the disease. For this reason, haemophilia was once popularly called "the royal disease".

2. Chapter 14 Mendel and the Gene Idea

3. Overview: Drawing from the Deck of Genes • The “particulate” hypothesis is the idea that parents pass on genes to their offspring. • Mendel documented a particulate mechanism through his experiments with garden peas. • Particles later named as genes

4. Concept 14.1: Mendel used the scientific approach to identify two laws of inheritance • Mendel discovered the basic principles of heredity by breeding garden peas in carefully planned experiments • Mendel’s career

5. Mendel’s Experimental, Quantitative Approach • Advantages of pea plants for genetic study: • They are available in many varieties. For example, one variety has purple flowers, while a contrasting variety has white flowers. • Short generation time and large # of offspring • Mendel could strictly control mating between plants. So he could always be sure of the parentage of the new seeds.

7. Self-pollination is natural in peas • Each pea flower has pollen-producing organs (stamens) and egg-producing organs (carpels). • Cross-pollination (fertilization between different plants) can be achieved by dusting one plant with pollen from another.

8. LE 14-2 To achieve cross-pollination select un-blossomed flower Remove immature stamens Dust pollen from another plant Each zygote resulted develops into an embryo and is seen as a pea Removed stamens from purple flower Transferred sperm- bearing pollen from stamens of white flower to egg- bearing carpel of purple flower Parental generation (P) Stamens Carpel Pollinated carpel matured into pod Planted seeds from pod Examined offspring: all purple flowers First generation offspring (F1)

9. Some genetic vocabulary • Character: a heritable feature, such as flower color, eye color • Trait: a variant of a character, such as purple or white flowers; black and brown eyes

10. Mendel chose to track only those characters that varied in an “either-or” manner such as: 1-Flower color (purple or white) 2- Flower position (axial or terminal) 3- Seed color (yellow or green) 4- Seed shape (round or wrinkled) 5- Pod shape (inflated or constricted) 6- Pod color (green or yellow) 7- Stem length (tall or dwarf) • Each variant for a character such as purple or white color for flowers is called a Trait.

11. Table 14-1

12. Mendel also made sure he started his experiments with varieties that were true-breeding, i.e. when the plants self-pollinate, all their offspring will have the same traits as the parents.

13. In a typical experiment, Mendel crossed two contrasting, true-breeding varieties, a process called hybridization • The true-breeding parents are the P generation • The hybrid offspring of the P generation are called the F1 generation • When F1 individuals self-pollinate, the F2 generation is produced

14. Mendelian genetics: Mendel’s quantitative analysis to deduction of laws • Mendel followed traits for at least three generations P, F1, and F2. He arrived at two principles of heredity that are known as: • 1- The law of segregation. • 2- the law of independent assortment.

15. The Law of Segregation: Traits separate in F2 generation • When Mendel crossed contrasting, true-breeding white and purple flowered pea plants, all of the F1 hybrids were purple • When Mendel self-pollinated the F1 hybrids, many of the F2 plants had purple flowers, but some had white • Mendel discovered a ratio of about three to one, purple to white flowers, in the F2 generation

16. Mendel reasoned that only the purple flower gene was affecting flower color in the F1 hybrids • Mendel called the purple flower color a dominant trait and white flower color a recessive trait • Reappearance of white in F2 • showed that it was not destroyed in F1 • Mendel observed the same pattern of inheritance in other six pea plant characters.

17. Mendel’s Model • Mendel used large sample sizes and kept accurate records • Mendel developed a hypothesis to explain the 3:1 inheritance pattern he observed in F2 offspring. • 3 : 1 is 75% : 25% • Cross ‘ROUND seed’ with ‘wrinkled seed’, guess results Four related concepts make up this model

18. Alterative versions of genes account for variations in inherited characters The first concept: • The gene for a particular character such as flower color resides at a specific position on a certain chromosome known as locus. • The gene for flower color in pea plants as an example exists in two versions, one for purple flowers and the other for white flowers. • These alternative versions of a gene are now called alleles Mendel was not aware of the term chromosome

19. LE 14-4 Allele for purple flowers Homologous pair of Chromosomes, one from eachparent(white and purple) Locus for flower-color gene Allele for white flowers The DNA nucleotide sequence varies in these two alleles located at flower-color-locus on the chromosome

20. The second concept: for each character, an organism inherits two alleles, one from each parent • Diploid zygote has two sets of chromosomes, one set from each parent, transferring inheritable traits • A genetic locus is actually represented twice. • These two alleles may be identical (P) or different (F1).

21. The third concept: • If the two alleles at a locus differ • Then one, the dominant allele, is fully expressed in the organism’s appearance • The other allele, the recessive allele, has no noticeable effect on the organism’s appearance in the presence of the dominant allele. Dominant allele is seen in the phenotype i.e it is expressed, do not think it can subdue recessive allele. They do not interact at all.Recessive allele also forms proteins but not seen differently in phenotype.

22. The fourth concept: • Now known as the law of segregation, states that the two alleles for a heritable character separate (segregate) during gamete formation and end up in different gametes • Thus, an egg or a sperm gets only one of the two alleles that are present in the somatic cells of an organism • Segregation corresponds to distribution of a pair of homologs at Anaphase I of meiosis I

23. Parent of a true-breed, has identical alleles hence all gametes have same allele • F1 offspring has one allele from purple and one allele from white, so 50% gametes get purple allele and ________? Allele for purple flowers Homologous pair of Chromosomes, one from eachparent(white and purple) Locus for flower-color gene Allele for white flowers

24. Mendel’s segregation model accounts for the 3:1 ratio he observed in the F2 generation of his numerous crosses. • Mendel derived the law of segregation by performing monohybrid crosses i.e. breeding experiments using parental varieties that differ in a single character such as flower color. • Monohybrid Cross: http://www.youtube.com/watch?v=F3AKldl6JZg

25. The combination resulting from a genetic cross may be predicted by using a Punnett Square. • A diagrammatic representation of combination of alleles • First determine alleles possible in each organism involved • A capital letter represents a dominant allele, and a lowercase letter represents a recessive allele http://www.youtube.com/watch?v=d4izVAkhMPQ&feature=related

26. LE 14-5_2 P Generation Purple flowers PP White flowers pp Appearance: Genetic makeup: p P Gametes F1 Generation Appearance: Genetic makeup: Purple flowers Pp Gametes: 1 1 p P 2 2 F1 sperm P p F2 Generation P PP Pp F1 eggs p Pp pp 3 : 1

27. Useful Genetic Vocabulary • An organism that is homozygous for a particular gene, also called a homozygote • Has a pair of identical alleles for that gene, such as homozygous dominant (PP) and homozygous recessive (pp) • Exhibits true-breeding, all gametes contain same allele in homozygous • An organism that is heterozygous for a particular gene, also called a heterozygote • Has two different alleles for a gene, such as (Pp). • Produce gametes with different allelesso not ______________?

28. Genetic composition is not always expressedbecause of different effect of dominant and recessive alleles • An organism’s phenotype • Is its physical appearance\ Observable traits\physiological traits • An organism’s genotype • Is its genetic makeup • In the example of flower color in pea plants, PPand Pp plants have the same phenotype (purple) but different genotypes

29. LE 14-6 Genotype Phenotype PP (homozygous Purple 1 Pp (heterozygous 3 Purple 2 Pp (heterozygous Purple pp (homozygous White 1 1 Ratio 1:2:1 Ratio 3:1

30. The Testcross • In pea plants with purple flowers • The genotype is not immediately obvious. • To determine whether an organism with dominant phenotype, such as purple flower color, is homozygous dominant (PP) or heterozygous (Pp) for the gene controlling flower color, we use a testcross.

31. LE 14-7 Dominant phenotype, unknown genotype: PP or Pp? Recessive phenotype, known genotype: pp If Pp, then 1 2 offspring purple and 1 2 offspring white: If PP, then all offspring purple: p p p p P P Pp Pp Pp Pp P P pp pp Pp Pp

32. Testcross • Testcross is the breeding of an organism of unknown genotype with a homozygous recessive individual. The proportion of phenotypes exhibited by the offspring will reveal the genotype of the unknown parent. • If all the offspring of the cross have purple flowers, then the mystery plant is homozygous for the dominant allele • If both purple and white phenotypes appear among the offspring then the mystery plant must be heterozygous

33. The Law of Independent Assortment • Mendel identified his second law of inheritance by following two characters at the same time • A dihybrid cross is a mating of parental varieties differing in two characters, such as seed color and seed shape in peas. • A monohybrid cross is a mating of parental varieties differing in one character, i.e heterozygotes of F1 are crossed. • Individuals of F1 generation are called monohybrids, obtained by crossing parents\ F0

34. Crossing two, true-breeding parents differing in two characters produces dihybrids in the F1 generation, heterozygous for both characters • Using a dihybrid cross, Mendel developed the law of independent assortment • The law of independent assortment states that each pair of alleles segregates independently of each other pairs of alleles during gamete formation.

35. Mendel knew from monohybrid crosses that Round and yellow are dominant alleles • For example, in the dihybrid YyRr, the two alleles for seed color (Yy) segregate independently of the two alleles for seed shape (Rr), so the alleles determining these traits behave as if they are on different chromosomes. • Y and R alleles are inherited independently

36. LE 14-8 P Generation YYRR yyrr Gametes yr YR YyRr F1 Generation Hypothesis of dependent assortment Hypothesis of independent assortment Sperm YR Yr yR yr 1 1 1 1 4 4 4 4 Sperm Eggs YR yr 1 1 2 2 YR 1 4 Eggs YYRR YYRr YyRR YyRr YR 1 2 F2 Generation (predicted offspring) YYRR YyRr Yr 1 4 YYRr YYrr YyRr Yyrr yr 1 2 YyRr yyrr yR 1 4 YyRR YyRr yyRR yyRr 3 1 4 4 yr 1 4 Phenotypic ratio 3:1 YyRr Yyrr yyRr yyrr 9 3 3 3 16 16 16 16 Phenotypic ratio 9:3:3:1

37. Pea plant has 14 chromosomes • In the dihybrid YyRr, four classes of gametes will be produced by the F1 generation: YR, Yr, yR, yr • there will be 9:3:3:1 phenotypic ratio in the F2 generation. i.e. 9/16 yellow round: 3/16 green round: 3/16 yellow wrinkled: 1/16 green wrinkled. • Law of independent assortment proves that, alleles segregate independently , do not stay together in crosses • Limitation: This law applies to only genes located on different chromosomes or non-homologous chromosomes or far apart on same chromosome (see Chap 15)

38. F2 phenotype only= 56%:19%:19%:6% • Write their genotypes???? • Now write genotypic ratio of the above dihybrid cross? • 1:2:2:4: 1:2 : 1:2 : 1 http://www.youtube.com/watch?v=9kAFEbhzz94 • Mendel tried different combinations of characters

39. Concept 14.3: Inheritance patterns are often more complex than predicted by simple Mendelian genetics • Complete dominance occurs when phenotypes of the heterozygote and dominant homozygote are identical. Because one allele in a pair showed complete dominance over the recessive alleleEx: Mendel’s classic pea crosses • There are other patterns of inheritance not described by Mendel, but his laws of segregation and independent assortment can be extended to these more complex patterns of inheritance.

40. The Spectrum of DominanceDeviations to Mendelian patterns • In codominance, two dominant alleles affect the phenotype in separate, distinguishable waysEx: MN blood type, black-tan cat, • In incomplete dominance, one allele is not completely dominant over the other, so the heterozygote has a phenotype that is intermediate between the phenotypes of the two homozygotes. Ex: Cross between red and white snapdragons give pink flowers in F1. So, is blending hypothesis true?

41. LE 14-10 Blending hypothesis is not true Interbreeding of F1 hybrids produces F2 offspring with 1:2:1 of red:pink:whiteBoth genotypic and phenotypic ratio for F2 are the same P Generation Red CRCR White CWCW Gametes CR CW Pink CRCW F1 Generation 1 1 Gametes CR CW 2 2 Sperm 1 1 CR CW 2 2 Eggs F2 Generation 1 CR 2 CRCR CRCW 1 CW 2 CRCW CWCW

42. Frequency of Dominant Alleles • Dominant alleles are not necessarily more common in populations than recessive alleles • For example, one baby out of 400 in the United States is born with extra fingers or toes, a condition known as polydactyly. • The allele for this unusual trait is dominant to the allele for the more common trait of five digits per appendage • In this example, the recessive allele is far more prevalent than the dominant allele in the population

43. Multiple Alleles: Many alleles, many phenotypes • Most genes exist in populations in more than two allelic forms • For example, 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: IA, IB, and i. • The enzyme encoded by the IA allele adds the A carbohydrate, whereas the enzyme encoded by the IB allele adds the B carbohydrate; the enzyme encoded by the i allele adds neither

46. Pleiotropy • When one gene has multiple phenotypic effects, this property is called pleiotropy • Pleiotropic alleles are responsible for the multiple symptoms associated with hereditary diseases, such as cystic fibrosis and sickle-cell disease. • Symptoms of sickle-cell disease include physical weakness, pain, organ damage, and even paralysis

48. Extending Mendelian Genetics for Two or More Genes • Some traits may be determined by two or more genes • Practice question: Types of gametes possible with this genotype XxYYZz.

49. Epistasis • In epistasis, a gene at one locus alters the phenotypic expression of a gene at a second locus • For example, in dogs and many other mammals, coat color depends on two genes • One gene determines the pigment color (with alleles B for black and b for brown) • The other gene (with alleles E for pigment color and e for no pigment color ) determines whether the pigment will be deposited in the hair

50. bb is _______ Black (B) is dominant over brown (b) Gene for pigment deposition is epistatic to the gene for pigment color. So E is epistatic over _B or b_ Hence, ee are yellow regardless of presence of B/b Ratio= 9:3:4 Figure 14.12 BbEe BbEe Sperm 1/4 1/4 1/4 1/4 Be BE be bE Eggs 1/4 BE BbEE BBEe BbEe BBEE 1/4 bE BbEE bbEe bbEE BbEe 1/4 Be BBEe BBee Bbee BbEe 1/4 be BbEe bbEe bbee Bbee : 3 9 : 4 Black: brown: yellow