1 / 74

Mendel & the Gene Idea

Mendel & the Gene Idea. Genetics. Scientific study of heredity Heredity: the transmission of genetic characters from parents to offspring: it is dependent upon the segregation and recombination of genes during meiosis and fertilization

adin
Download Presentation

Mendel & the Gene Idea

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. Mendel & the Gene Idea

  2. Genetics • Scientific study of heredity • Heredity: the transmission of genetic characters from parents to offspring: • it is dependent upon the segregation and recombination of genes during meiosis and fertilization • it results in the creation of a new individual similar to others of its kind but exhibiting certain variations

  3. Gregor Mendel • Lived 1822- 1884 • Father of Genetics • Austrian Monk • In charge of the monastery garden • Discovered the basic principles of heredity by breeding garden pea plants in carefully planned experiments

  4. So why choose Peas? • Easy to work with & readily available • Many traits known • Short life span • Many varieties • Character: a heritable feature, such as flower color • Trait: each variation of a character, such as white or purple flower color

  5. Bisexual • Easy to control mating  Each flower has both male & female reproductive organs • Stamen produces pollen • You can selectively remove them while they’re immature to prevent unknown pollination • Cross pollination • Self-pollinastion • Carpel produces eggs • (You can eat the failures).

  6. Self Pollination • One flower as both parents • Natural event in peas • Results in pure-bred offspring where the offspring are identical to the parents • Continued self pollination typically results in true breeding organisms

  7. Different Types of Hybridization • P generation = parental generation • True breeding parents • F1 generation = 1st filial or 1st generation of offspring • F2 generation = 2nd filial, or 2nd generation of offspring

  8. Monohybrid Crosses • Crosses that work with a single character at a time. Example - Tall X short P1 Tall X short (TT x tt) F1 all Tall (Tt) F2 3 tall to 1 short (1 TT: 2 Tt: 1 tt)

  9. Mendels Work Mendels Results Mendels Hypotheses • In all crosses, the F1 generation showed only one of the traits regardless of which wasmaleorfemale. • The other trait reappeared in the F2 at ~25% (3:1 ratio). • Genes can have alternate versions called alleles. • Each offspring inherits two alleles, one from each parent • If the two alleles differ, the dominantallele is expressed. The recessive alleleremains hidden unless the dominant allele is absent. from each parent • The two alleles for each trait separate during gamete formation

  10. Mendes Work • Used seven characters, each with two expressions or traits. • Example: Character - height • Traits - tall or short • Mendels quantitative analysis of the F2 plants revealed the 2 fundamental principles of heredity • Law of Segregation • Law of Independent Assortment

  11. Law of Segregation

  12. Definitions You Need to Know • Gene: sequence of DNA that codes for a protein and thus determines a trait • Allele: 1 of a number of different forms of a gene • Homozygous: pair of identical alleles for a trait • Heterozygous: Having 2 different alleles for a trait • Genotype: an organisms genetic makeup • Phenotype: an organisms outward appearance • Gamete: A reproductive cell having the haploid number of chromosomes, especially a mature sperm or egg capable of fusing with a gamete of the opposite sex to produce the fertilized egg

  13. 6 Mendelian Crosses are Possible CrossGenotypePhenotype TT X tt all Tt all Dom Tt X Tt 1TT:2Tt:1tt 3 Dom: 1 Res TT X TT all TT all Dom tt X tt all tt all Res TT X Tt 1TT:1Tt all Dom Tt X tt 1Tt:1tt 1 Dom: 1 Res

  14. Test Cross • Cross of a suspected heterozygote with a homozygous recessive. • Ex: T_?_ X tt If TT - all dominant If Tt - 1 Dominant: 1 Recessive

  15. Time to make it harder Dihybrid Crosses • Cross with two genetic traits. • Need 4 letters to code for the cross. • Ex: TtRr • Each Gamete - Must get 1 letter for each trait. • Ex. TR, Tr, etc. • You must 1st determine the # of kinds of gametes • Critical to calculating the results of higher level crosses. • Look for the number of heterozygous traits.

  16. Equation for determining the # of types of gametes • The formula 2n can be used, where “n” = the number of heterozygous traits. • Ex: TtRr, n=2 • 22 or 4 different kinds of gametes are possible. • TR, tR, Tr, tr

  17. Dihybrid Cross TtRr X TtRr Each parent can produce 4 types of gametes. TR, Tr, tR, tr Cross is a 4 X 4 with 16 possible offspring. • Results of a dihybrid cross between 2 completely heterozygpous parents • 9 Tall, Red flowered • 3 Tall, white flowered • 3 short, Red flowered • 1 short, white flowered • Or 9:3:3:1 ratio

  18. Law of Independent Assortment • The inheritance of 1st genetic trait is NOT dependent on the inheritance of the 2nd trait. • Inheritance of height is independent of the inheritance of flower color.

  19. Genetics & Probabilty • Ratio of Tall to short is 3:1 • Ratio of Red to white is 3:1 • The cross is really a product of the ratio of each trait multiplied together. • (3:1) X (3:1) • Genetics is a specific application of the rules of probability. • Probability - the chance that an event will occur out of the total number of possible events.

  20. Genetic Ratios • The monohybrid “ratios” are actually the “probabilities” of the results of random fertilization. • Ex: 3:1 • 75% chance of the dominant • 25% chance of the recessive • Rule of multiplication • The probability that two alleles will come together at fertilization, is equal to the product of their separate probabilities.

  21. Example: TtRr X TtRr • The probability of getting a tall offspring is ¾. • The probability of getting a red offspring is ¾. • The probability of getting a tall red offspring is ¾ x ¾ = 9/16

  22. Use the Product Rule to calculate the results of complex crosses rather than work out the Punnett Squares. • Ex: TtrrGG X TtRrgg “T’s” = Tt X Tt = 3:1 “R’s” = rr X Rr = 1:1 “G’s” = GG x gg = 1:0 Product is: (3:1) X (1:1) X (1:0 ) = 3:3:1:1

  23. Variations on Mendel 1. Incomplete Dominance 2. Codominance 3. Multiple Alleles 4. Epistasis 5. Polygenic Inheritance

  24. Incomplete Dominance • When the F1 hybrids show a phenotype somewhere between the phenotypes of the two parents. • Ex. Red X White snapdragons • F1 = all pink • F2 = 1 red: 2 pink: 1 white

  25. Results • No hidden Recessive. • 3 phenotypes and 3 genotypes (Hint! – often a “dose” effect) • Red = CR CR • Pink = CRCW • White = CWCW • Another example of incomplete dominance

  26. CoDominance • Both alleles are expressed equally in the phenotype. • Ex. MN blood group • MM • MN • NN • No hidden Recessive. • 3 phenotypes and 3 genotypes (but not a “dose” effect) • Another example of codominance

  27. Blood Type is CoDominant

  28. Rh Factor is a separate factor in blood type • Rh blood factor is a separate factor from the ABO blood group. • Rh+ = dominant • Rh- = recessive • A+ blood = dihybrid trait

  29. Epistasis • When 1 gene locus alters the expression of a second locus. • Ex: • 1st gene: C = color, c = albino • 2nd gene: B = Brown, b = black CcBb X CcBb Brown X Brown F1 = 9 brown (C_B_) 3 black (C_bb) 4 albino (cc__)

  30. Epistasis in Mice

  31. Problem • Wife is type A • Husband is type AB • Child is type O Question - Is this possible? Comment - Wife’s boss is type O UH OH…. Whose your baby daddy (Maybe mom’s a hussy!)

  32. Bombay Effect • It is a new blood group discovered in Maharashta India, & is found in people who have the A or B genes, but test as type O • Only 0.001% of the Indian population have this blood type • They can only receive blood transfusion from other Bombay blood types • It is due to an Epistatic Gene on ABO group, which alters the expected ABO outcome. • H = dominant, normal ABO • h = recessive, no A,B, reads as type O blood.

  33. You have to look at the parental genotypes • Wife: type A (IA IA, Hh) • Husband: type AB (IAIB, Hh) • Child: type O (IA IA, hh) • Therefore, the child is the offspring of the wife and her husband (and not the boss). • When ABO blood type inheritance patterns are altered from expected.

  34. Polygenic Inheritance • Factors that are expressed as continuous variation. • Lack clear boundaries between the phenotype classes. • Ex: skin color, height • Several genes govern the inheritance of the trait. • Ex: Skin color is likely controlled by at least 4 genes. Each dominant gives a darker skin.

  35. Result • Mendelian ratios fail. • Traits tend to "run" in families. • Offspring often intermediate between the parental types. • Trait shows a “bell-curve” or continuous variation.

  36. Genetic Studies in Humans • Often done by Pedigree charts. • Why? • Can’t do controlled breeding studies in humans. • Its frowned apon, ask Hitler • Long life-history pattern • Mature slowly • Long life span • Reproduce later in life • Small number of offspring.

  37. Domoinant Trait Recessive Trait

  38. Human Recessive Disorders • Several thousand known: • Albinism • Sickle Cell Anemia • Tay-Sachs Disease • Cystic Fibrosis • PKU • Galactosemia

  39. Sickle-Cell Disease • Most common inherited disease among African-Americans. • Single amino acid substitution results in malformed hemoglobin. • Reduced O2 carrying capacity. • Codominant inheritance.

  40. Metabolic Disorders • Enzymes are chemical compounds that increase the rate at which reactions take place in a living organism. • as a group these chemical reactions are referred to as metabolism • Without enzymes, most chemical changes in an organism would proceed so slowly that the organism could not survive. • If an enzyme is missing from the body or not functioning as it should, a metabolic disorder may develop.

  41. Tay-Sachs Disease • Is a fatal genetic lipid storage disorder in which harmful quantities of a fatty substance called ganglioside GM2 build up in tissues and CNS • Is common to people of Jewish and eastern European descent

  42. Tay-Sachs Disease • Inheriting this recessive disorder results in your bodies inability to make a functional enzyme called beta-hexosaminidase A • normally breaks down acidic fatty materials known as gangliosides that are produced and stored in tissues of the CNS, causing the lipid to accumulate in the cells

  43. Tay-Sachs • Infants with Tay-Sachs disease appear to develop normally for the first few months of life. • As nerve cells become distended with fatty material, a relentless deterioration of mental and physical abilities occurs. • Child becomes blind, deaf, and unable to swallow. Muscles begin to atrophy and paralysis sets in

  44. Cystic Fibrosis • Produces defective chloride channels inmembranes results in the formation of thick mucus in the lungs and digestive tract

  45. Most common lethal genetic disease in the U.S. • Most frequent in Caucasian populations • 1 in 28 is a carrier • 1 in 2,500 children have the disease

More Related