Genetics

1. Genetics

2. The Study of Heredity Heredity • The passing of traits from parents to their offspring Causes children to resemble their parents.   • Genetics- The study of heredity

3. The Study of Heredity Gregor Mendel - the father of modern genetics • Austrian monk - trained in mathematics and natural sciences.   • Work conducted over period of 8 years with common garden peas -1856 to 1865.   Kept careful records.   Applied mathematical studies to his work.   Worked with different kinds of plants.   Selected peas  

4. The Study of Heredity

5. The Study of Heredity Selected peas because they:   • Grew rapidly.   • Produced many seed (offspring).   • Flower structure made it easy to control Pollination Transfer of pollen from stamen to pistil of a flower.   Pistil- female reproductive structure - egg at base.   Stamen- male reproductive structure - produces pollen contains sperm.   Self –pollination- process where pollen from stamen falls on pistil of the same flower.   Cross-pollination- process where pollen from stamen of 1 flower falls on pistil of another flower on another plant.

6. The Study of Heredity

7. The Study of Heredity Identified 7 different characteristics in pea plants Each had two contrasting forms.   • Seed Shape - Round Vs. Wrinkled   • Seed Color - Yellow Vs. Green   • Flower Color - Purple Vs. White   • Pod Shape - Inflated Vs. Constricted   • Pod Color - Green Vs. Yellow   • Flower Position - Axial Vs. Terminal   • Plant Height - Tall Vs. Short

8. The Study of Heredity

9. The Study of Heredity His experiments were different from earlier workers • Studied only 1 trait at a time, rather than everything about the offspring at once.   • Studied results of many matings and pooled the results - earlier workers had looked at only a few offspring from a single mating   Counted 7324 peas for seed shape (F2 generation)   Counted 8023 peas for seed color (F2 generation)   • Used the large number of offspring to discover definite ratios of characteristics among the offspring.   5474 Round Seed: 1850 Wrinkled Seed 2.96:1   6022 Yellow Seed: 2001 Green Seed 3.01:1  

10. The Study of Heredity Mendel's Experiments and Observations • When the plants were allowed to self-pollinate, the trait always stayed the same - called them "Truebreeding" or "Pure"plants; Tall plants x Tall plants produced Tall plants. • Removed stamens from the pure plants that produced wrinkled seeds. Dusted pistil with pollen from plants that produced only round seeds Called these the Parental or P1 generation • All of the offspring of this cross resulted in plants that had round seed Called this the First Filial or F1 generation; Also called Hybrids Hybrid- offspring from a cross between parents differing in 1 or more traits. Found that 1 trait of the parents always disappeared in the F1 generation. • The F1 generation plants were allowed to self-pollinate   Called the next generation the Second Filial or F2 generation.   Found that some F2 plants had round seed; some had wrinkled seeds.   Similar results were obtained with the other traits always 75% of 1 trait; 25% of other trait - a 3:1 ratio.  

11. The Study of Heredity Mendel’s Cross P1 Round Seed x Wrinkled Seed F1 All Hybrid Round Seed Hybrid Round Seed x Hybrid Round Seed F2 ¾ Round Seed; ¼ Wrinkled Seed

12. The Study of Heredity Mendel's Conclusions   • Did not know anything about cell reproduction Work based on hypothesis that Factorsor units carried the traits he was studying - called Genestoday.   • Observed that offspring of true breeding plants with contrasting traits showed the trait of only 1 parent plant Called trait Dominant– disappearing trait called Recessive • Observation lead to his Law of Dominance - one form of a hereditary trait, the dominant trait, Dominatesor prevents the expression of the recessive trait.   • Mendel hypothesized that factors exist in pairs since the plants which had 1 trait could produce seeds with the opposite trait.  

13. The Study of Heredity Mendel’s Conclusions • Mendel hypothesized that paired factors separate or segregate during gamete formation - lead to Law of Segregation - During gamete formation the pairs of genes responsible for each trait separate so that each gamete contains only 1 gene for each trait.   •  During fertilization the zygote gets 1 gene for the trait from mom and 1 from dad.   • The different forms of a gene for a trait are known as Alleles • Combination of alleles or genetic makeup is the organism’s Genotype   • The appearance of the organism regardless of its genetic makeup is its - physical appearance - Round, yellow, etc.  

14. The Study of Heredity

15. The Study of Heredity • Dominance is expressed by a capital letter - usually the first letter of the dominant trait; Recessive trait is expressed by a small letter (same as the dominant trait)   For round Vs. wrinkled seed - R - dominant; r - recessive   Hybrid would be Rr   • During gamete formation the pairs of genes responsible for each trait separate so that each gamete contains only 1 gene for each trait.     Rr   / \ R r  

16. The Study of Heredity Mendel’s Cross P1 Round Seed x Wrinkled Seed RR x rr F1 All Hybrid Round Seed (Rr) Hybrid Round Seed x Hybrid Round Seed Rr x Rr F2 ¾ Round Seed; ¼ Wrinkled Seed RR, Rr rr

17. The Study of Heredity

18. The Study of Heredity Genetic Terminology • Dominant - trait which stays visible • Recessive - trait which disappeared • Alleles - alternate forms of a gene for a trait   • Genotype - genetic makeup of a trait   • Phenotype - physical appearance of a trait   • Homozygous - both alleles are the same   • Heterozygous - two alleles are different • Homozygous Dominant - pure dominant  • Homozygous Recessive - pure recessive   • Heterozygous Dominant - Hybrid with 1 dominant -

19. The Study of Heredity Mendel’s Laws • LAW OF DOMINANCE - one form of a hereditary trait, the dominant trait, dominatesor prevents the expression of the recessive trait. • LAW OF SEGREGATION - During gamete formation the pairs of genes responsible for each trait separate so that each gamete contains only 1 gene for each trait. • LAW OF INDEPENDENT ASSORTMENT - Alleles segregate independently of each other during gamete formation.  

20. Probability The likelihood of an event occurring as expressed as a ratio or a percentage.   • Flipping a coin – ½ heads; ½ tails   • Cards -   Chance of drawing an ace –4/52 or 1/13   Chance of drawing a spade - 13/52 or 1/4   Chance of drawing the Ace of Spades 1/13 x 1/4 = 1/52  

21. Probability Product Rule   • To find the probability of 2 events occurring you multiply the individual probabilities.   Chance of a head – ½ ; Chance of another head – ½   Chance of 2 heads in a row – ½ x ½ = ¼   Chance of 4 heads in a row – ½ x ½ x ½ x ½ = 1/16   • Each gamete has ½ chance of getting a particular allele   Homozygous Dominant - RR: Alleles - R or R = 1/1   Homozygous Recessive - rr: Alleles - r or r = 1/1   Heterozygous Dominant - Rr: Alleles - R or r; ½ R; ½ r  

22. Probability PUNNETT SQUARE   • Special chart used to show possible combinations resulting from a cross of 2 organisms.   • Put female gametes along top; male gametes along left side   • Squares show possible genotypes of offspring -used to determine phenotype and ratio of offspring.   • Used to predict; it doesn’t mean it will happen

23. Types of Crosses MONOHYBRID CROSS - involves only one set of contrasting factors for a trait   • Cross a homozygous yellow with a homozygous green   Yellow – dominant (Y); green - recessive (y)  Y Y P1 YY x yy y F1 all Yy heterozygous yellow y   • Cross two of the F1 generation   Y y Yy x Yy Y F2 – ¼ YY; ½ Yy; ¼ yy ¾ Yellow; ¼ green y Yy Yy Yy Yy YY Yy Yy yy

24. Types of Crosses DIHYBRID CROSS - involves two sets of contrasting traits at one time; genes are on separate chromosomes   • Each gamete contains 1 allele for each trait   • LAW OF INDEPENDENT ASSORTMENT - Alleles segregate independently of each other during gamete formation.  

25. Types of Crosses Het Round, Het Yellow RrYy x Het Round, Het Yellow RrYy Gametes: RY Ry rY ry

26. Types of Crosses INCOMPLETE DOMINANCE/NONDOMINANCE • Phenotype between dominant and recessive trait   • Heterozygous condition   • Example - Four-O-Clocks   RR - red flowers   rr - white flowers   Rr - Pink flowers   • Cross of 2 pink flower plants - Rr x Rr   Results – ¼ red (RR); 2/4 (½) Pink (Rr); ¼ white  

27. Types of Crosses

28. Types of Crosses Determination of Sex   • By the Sex Chromosomes- x or y Other chromosomes are called Autosomes • Male - xy; Female - xx   • Get ½ males and ½ females on Punnett square x x x y xx xx xy xy

29. Types of Crosses

30. Types of Crosses SEX LINKED CHARACTERISTICS   • Recessive trait linked with a certain sex - usually males   • Carried on the x-chromosome; Male has only 1 x, the trait is visible Females with 2 x's - not visible if 1 of the x has a dominant gene for the trait.   • Female only shows trait in homozygous recessive.   • Woman is called a "Carrier" in heterozygous condition.   • Examples:   Red-Green color blindness   Hemophilia  

31. Types of Crosses Male Female

32. Types of Crosses

33. Types of Crosses MULTIPLE ALLELES • More than 2 alleles exist for a particular trait   • In humans - blood types is an example of multiple alleles   3 different alleles - A, B, O   Alleles A and B are codominant O is recessive

34. Types of Crosses Blood Type • Due to presence of antigens on the red blood cells - produces antibodies in blood   Type A - Antigen A on cells Plasma contains anti B   Type B - Antigen B on cells Plasma contains anti A   Type O - No Antigens on cells Plasma has anti A and anti B   Type AB - Antigens A and B on cells Plasma lacks anti A and anti B

35. Types of Crosses

36. Types of Crosses Phenotypes and genotype combinations   • Type A - AA or AO   • Type B - BB or BO   • Type AB - AB   • Type O - OO

37. Types of Crosses Blood Donor Receives Group to from O O, A, B, AB O Universal Donor A A, AB O, A B B, AB O, B AB AB O, A, B, AB Universal Recipient

38. Other Related Topics GENE LINKAGE   • Concerned with the presence of 2 different genes on the same chromosome   • Does not follow usual dihybrid results - follows monohybrid.   • Variation can occur due to crossing over - pieces of chromatids exchange places during synapsis of tetrads in meiosis.  

39. Other Related Topics LETHAL GENES • Genes which can cause death or harm in the homozygous condition.   • Examples:  Sickle-cell anemia   PKU   Tay Sachs - Jews of middle eastern European origin.   Diabetes mellitus  

40. Other Related Topics

41. Other Related Topics NONDISJUNCTION   • Failure of chromosomes to segregate properly during gamete formation.   • Can involve sex chromosomes as well as the autosomes - zygote gets an improper number of chromosomes   • Examples:   Down's Syndrome - three #21 chromosomes - autosomal   Turner's Syndrome - has only 1 x, no y chromosome - female   Klinefelter's Syndrome - xxy - male   Jacob’s Syndrome- xyy - male –thought to show criminal behavior at one time; not any higher.

42. Other Related Topics Normal Male Male – Down’s

43. Other Related Topics Klinefelter’s Syndrome Turner’s Syndrome Jacob’s Syndrome

44. Other Related Topics MUTATIONS   • Change in the genetic code or genes of an organism.   • Can occur naturally or by exposure to agents that produce mutations.   Breaks during crossing over which do not reattach.   Increased chance of breakage by exposures to mutagens   Mutagens- agents that cause mutations.   Radiation - x-rays, UV, gamma   Chemicals