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Mendel’s Genetics

Learn about Mendel's experiments with pea plants and his discovery of the laws of segregation and independent assortment in genetics. Explore the concepts of dominant and recessive alleles, genotype and phenotype, and the principles of complete dominance and incomplete dominance. Discover how these principles explain the inheritance of traits like hair color.

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Mendel’s Genetics

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  1. Mendel’s Genetics

  2. Where did that blonde hair come from?law of segregation and random assortment 23 23 46 23 23 23 23

  3. Intro notes

  4. GENETICS and EVOLUTION • The purpose of this chapter is to show how genetic traits are passed from one generation to another. This is called HEREDITY • If there was no genetic variation through mutation or crossing over of genes there would be no evolution

  5. Gregor Mendel The Monastery

  6. I. Gregor Mendel- the father of genetics theory (1822-1884) A. Background 1. entered monastery at 21 2. studied math and science at University of Vienna 3. 1857-1865 – investigated inheritance in pea plants

  7. B. Peas – A Fortunate Choice (Pisum sagivum) 1. seven distinct characteristics (flower color, flower position, seed color, seed shape, pod shape, pod color, height) 2. easy to grow 3. mature quickly 4. easy to pollinate

  8. D. Mendel’s Experiments-monohybrid crosses (one purple & one white parent) 1. P1 Generation (Parental) a. crossed plants pure for a trait – TRUE- BREEDING 2. F1 Generation (Offsprng of P1) a. all plants show one form of the trait 3. F2 Generation (Offsprng of F1) a. show forms of trait in 3:1 ratio

  9. Mendel’s P, F1and F2 Generations

  10. Examples of P1 Cross Tall X Short(both are pure) T T X t t All offspring are tall (T t) F1 Generation F1 Generation (all are hybrids) Purple Flower X White Flower(both pure)P P X p p All offpsring are purple (Pp) F1 Generation F1 Generation (all are hybrids)

  11. Mendel’s F1 Cross (hybrid x hybrid) Tall X Tall (hybrid cross) T t X T t 3 tall plants : 1 short plant (F2 Generation) Ratio of 3:1 Purple Flowers X Purple Flowers (hybrid) P p X P p 3 purple flower plants : 1 white flower (F2) Ratio of 3:1

  12. II. Vocabulary A. Dominant(represented by upper case letter) 1. allele that masks the recessive allele for the same characteristic B. Recessive(represented by lower case letter) 1. allele that is masked by the dominant allele for the same characteristic

  13. II. Vocabulary C. Genotype 1. genetic makeup 2. examples a. TT, Tt, tt, b. PP, Pp, pp D. Phenotype 1. external appearance 2. examples a. tall, short b. purple flowers, white flowers

  14. E. Homozygous (pure) 1. two alleles code for the same trait 2. examples a. TT, tt, PP, pp F. Heterozygous(hybrid) 1. two alleles do not code for the same trait 2. examples a. Tt and Pp

  15. III. Complete Dominance (Monohybrid Cross) A. Both parents are pure 1. homozygous x homozygous 2. example T T x t t B. Both parents are hybrid 1. heterozygous X heterozygous 2. example Tt x Tt

  16. III. Complete Dominance C. Pure parent X hybrid parent 1.homozygous dominant X heterozygous a. Example T T x T t 2.homozygous recessive x heterozygous a. Example tt x Tt

  17. PUNNETT SQUARES

  18. MENDEL”S THEORY • 1. Each individual has two copies of an individual trait -these traits controlled by a pair of factors a. today factors are called alleles 2. There are alternate versions traits • TT = tall tall Tt= tall short tt= short short

  19. MENDEL”S THEORY • 3. One trait may be expressed and other may not have an effect. • dominant and recessive

  20. Analysis of Mendel’s Results 1. Principle of Dominance a. one factor (gene) can prevent expression of another (dominance) IE: hybrid tall plant – phenotype- tall genotype- Tt

  21. 2. Law of Segregation a. a pair of factors separate when gametes form 3. Law of Independent Assortment a. factors (genes) for different characteristics separate independently

  22. Animation: The Inheritance of Single Traits

  23. WORK ON Inheritance lab

  24. Where did that blonde hair come from?law of segregation and random assortment 23 23 46 23 23 23 23

  25. incomplete /co dominance/sex linked • www.youtube.com/watch?v=fQvER3MyI2c

  26. Incomplete Dominance/blended traits • The phenotype of an individual is the intermediate trait between the two parents: • Or-When two heterozygous genotypes make a third, different phenotype. • EXAMPLES: • Straight haired mother and curly haired father- the child will have an intermediate trait such as wavy hair • Red snapdragon when crossed with white snapdragons produce pink snapdragons.

  27. 10.5 Do the Mendelian Rules of Inheritance Apply to All Traits? In incomplete dominance, the phenotype of the heterozygotes is intermediate between the phenotypes of the homozygotes In the genes studied by Mendel, one allele was dominant over the other, which was recessive Some alleles, however, are incompletely dominant over others When the heterozygous phenotype is intermediate between the two homozygous phenotypes, the pattern of inheritance is called incomplete dominance

  28. 10.5 Do the Mendelian Rules of Inheritance Apply to All Traits? In incomplete dominance, the phenotype of the heterozygotes is intermediate between the phenotypes of the homozygotes (continued) Human hair texture is influenced by a gene with two incompletely dominant alleles, H1 and H2 A person with two copies of the H1 allele has curly hair Someone with two copies of the H2 allele has straight hair Heterozygotes (with the H1H2 genotype) have wavy hair

  29. 10.5 Do the Mendelian Rules of Inheritance Apply to All Traits? In incomplete dominance, the phenotype of the heterozygotes is intermediate between the phenotypes of the homozygotes (continued) If two wavy-haired people marry, their children could have any of the three hair types: curly (H1H1), wavy (H1H2), or straight (H2H2)

  30. 10.5 Do the Mendelian Rules of Inheritance Apply to All Traits? A single gene may have multiple alleles An individual may have at most two different gene alleles A species may have multiple alleles for a given characteristic However, each individual still carries two alleles for this characteristic

  31. IV.Incomplete Dominance (both alleles influence the trait) A. Pure X Pure = all hybrids 1.example (red flower and white flower) a. RR x WW B. Hybrid X Hybrid 1. e (pink x pink flower)a. RW x RW C. Pure X hybrid 1.ex (red x pink or white x pink) a. RR x RW or WW x RW

  32. Incomplete Dominance Four O’clock Flowers Pink (RW) White (WW) Red (RR)

  33. Codominanttraitsboth are shown- zebra • Both traits are shown – for instance the person with AB blood type is a child with one parents that was A blood type and one parent with B blood type. • Neither trait is dominant. Both are in the genotype and phenotype.

  34. V. Codominance (both alleles are expressed) A. Pure X Pure 1. example (white horse x red horse) a. WW x RR B. Hybrid x Hybrid 1.example(roan horse x roan horse) a. RW x RW C. Pure X Hybrid 1. example(redxroan /white xroan) a. RR x RW or WW x RW

  35. A. PHENOTYPE Type A Type B Type AB Type O B. GENOTYPE AA, AO( IAIA , IAi ) BB, BO( IBIB , IBi ) AB ( IA IB ) OO( ii ) VI. Multiple Allele Problems (Blood Types)

  36. Table 10-1

  37. Blood Donors and Recipients

  38. VII. Sex-linked Inheritance (X linked-carried on X chromosome) A. Examples of sex-linked traits 1. color blindness 2. hemophilia 3. muscular dystrophy 4. Icthyosis

  39. Normal Male Male with Disease Normal Female Female Carrier Female - Disease X Y X* Y X X X* X X* X* Individual Chromosomes

  40. Problem Solving- Sex Linked Diseases A. A man is colorblind and his wife is a carrier for colorblindness. What is the probability that they will have a child who is colorblind? (A son? A daughter?) B. A man and woman are both colorblind. Can they have a child who is not colorblind? (A son? A daughter?)

  41. Website –sex linked traits • www.edc./weblabs • http://www.biology.arizona.edu/mendelian_genetics/problem_sets/sex_linked_inheritance/sex_linked_inheritance.html

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