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GENETICS

Learn about Gregor Mendel, the "Father of Genetics," and his experiments on pea plants that led to the discovery of genetic laws such as the Law of Segregation and Law of Independent Assortment. Understand important genetic terms and concepts like genotype, phenotype, homozygous, heterozygous, and Punnett squares.

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GENETICS

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  1. GENETICS THE FIELD OF BIOLOGY DEVOTED TO UNDERSTANDING HOW CHARACTERISTICS ARE PASSED FROM PARENT TO OFFSPRING.

  2. GREGOR MENDEL (1823 – 1884) AUSTRIAN MONK WHO STUDIED MATH & STATISTICS. HE BECAME KNOWN AS THE “FATHER OF GENETICS”. HE CONDUCTED EXPERIEMENTS ON PEA PLANTS.

  3. MENDEL’S PEA PLANT EXPERIEMENTS He observed 7 characteristics of pea plants each characteristic had only 2 contrasting traits. - height - flower position along the stem - pod appearance - pod color - seed texture - seed color - flower color

  4. MENDEL’S EXPERIMENT 1.GREW ONLY PLANTS THAT WERE PURE FOR EACH TRAIT. -he had plants self-pollinate for several generations. 2. CROSS-POLLINATED CONTRASTING TRAITS. -ex: he crossed a yellow pod plant with a green. 3. THE 1ST CROSS WAS LABELED AS THE PARENTAL GENERATION (P).

  5. 4. THE OFFSPRING WERE LABELED AS THE F1 GENERATION 5. MENDEL ALLOWED THE F1 GENERATION TO SELF-POLLINATE & THOSE OFFSPRING WERE THE F2 GENERATION.

  6. MENDEL’S RESULTS AFTER CROSSING A PURE GREEN PODDED PLANT (P) WITH A PURE YELLOW (P)ALL OF THE OFFSPRING WERE GREEN. AFTER THESE OFFSPRING (F1) WERE CROSSED THE RESULTING OFFSPRING (F2) CAME OUT TO A 3 TO 1 RATIO FOR GREEN PODDED PLANTS.

  7. MENDEL’S LAWS LAW OF SEGREGATION - -Reproductive cells only receive one factor of each pair. LAW OF INDEPENDENT ASSORTMENT: -The factors for different characteristics are not connected

  8. QUESTION EXPLAIN WHY MENDEL GOT THE RESULTS HE DID WITH THE PARENTAL GENERATION?

  9. ANSWER Because the green color is considered dominant & it covers or masks the yellow color trait.

  10. QUESTION If all of the offspring were green and then they were cross pollinated, why didn’t these offspring come out all green?

  11. ANSWER Because the offspring from F1 generation carried a hidden yellow factor that could be passed on to the offspring of F2 generation.

  12. GENETIC TERMS • Gene: a sequence of DNA that encodes for a certain trait • Allele: one of two (or more) alternative forms of a gene (a single letter) • Dominant Allele: an allele that dictates the expression of a trait (capital letter, ex: A) • Recessive Allele: an allele whose trait is masked by the presence of a dominant allele (lower case letter, ex: a)

  13. TERMS Genotype: genetic make-up of an organism (letter combination) Phenotype: physical appearance of an organism (its outward appearance) Homozygous: both alleles in a gene pair code for the same trait (ex: AA or aa) Heterozygous: the two alleles in a gene pair that do not code for the same trait (ex: Aa)

  14. TERMS Sex Chromosome: the chromosome that determines the sex of an organism (the X and Y chromosome) Autosome: any chromosome that is not a sex chromosome Punnett Square: a chart which shows all possible gene combinations in a cross of parents Monohybrid cross: a cross between two individuals for one trait (ex: Aa x Aa) Dihybrid cross: crossing two different characteristics at the same time (AaBb x AaBb)

  15. TERMS Genotypic Ratio: the number of times each genotype appears in the offspring. Written from most dominant trait to the recessive. Phenotypic Ratio: the number of times each phenotype appears in the offspring. Written from the dominant trait to the recessive. Law of Segregation: factors that control a trait maintain a discrete identity when passed from parent to offspring.

  16. Punnett Squares T T t t T T t TT x tt A Punnettsquare is a chart which shows all possible gene combinations in a cross of parents. • Horizontally across the top of the chart are the possible gametes of one parent. • Vertically down the side of the chart are the possible gametes of the other parent. • In the boxes of the chart are the possible genotypes of the offspring. t t t T T

  17. B= brown eyes b= blue eyes Monohybrid Cross: two heterozygous individuals Bb x Bb GENOTYPIC RATIO: 1:2:1 BB:Bb:bb B b Homozygous dominant: Heterozygous: Homozygous recessive B BB Bb PHENOTYPIC RATIO: Bb b bb 3:1 Brown:Blue Dominant:Recessive

  18. LET’S TRY ANOTHER ONE!!!! B= brown eyes b= blue eyes Bb x bb B b The genotypic ratio is: The phenotypic ratio is: 0:2:2 b b 2:2 1:1

  19. HOW DID MENDEL FIGURE OUT IF THE PURPLE FLOWERING PLANTS WERE HOMOZYGOUS DOMINANT OR HETEROZYGOUS?

  20. The Testcross • A genetic procedure devised by Mendel to determine an individual’s actual genetic composition • A purple-flowered plant can be homozygous dominant (PP) or heterozygous (Pp) • One cannot tell by simply looking at the phenotype • One can tell from the results of a cross between the test plant and a homozygous recessive plant

  21. How Mendel used the testcross to detect heterozygotes.

  22. DIHYBRID CROSS PpQq x PpQq Crossing 2 different characteristics at the same time.

  23. P generation Round, yellow Wrinkled, green Analysis of a dihybrid cross

  24. RrYy x RrYy Phenotypic Ratio

  25. Dihybrid Cross EH EH eH eH Cross EeHH EeHH EH EEHH EEHH EeHH & EeHh Eh EeHh EEHh EEHh EeHh E= Brown eyes e= Blue eyes eeHH eH EeHH EeHH eeHH H= Brown hair EeHh EeHh eeHh eeHh eh h= Blond hair

  26. What does an offspring need to have to have brown eyes and brown hair? What is the chance of having that? AND THE PHENOTYPIC RATIO IS…. 12/16 Needs an E and H What does an offspring need to have to have brown eyes and blond hair? What is the chance of having that? Needs an E and hh 0/16 What does an offspring need to have to have blue eyes and brown hair? What is the chance of having that? Needs an ee and H 4/16 What does an offspring need to have to have blue eyes and blond hair? What is the chance of having that? 12:0:4:0 Needs an ee and hh 0/16

  27. How Genes Influence Traits • Genes specify the amino acid sequence of proteins • The amino acid sequence determines the shape and activity of proteins • Proteins determine a majority of what the body looks like and how it functions • Mutations in a gene result in new alleles • This ultimately leads to a change in the amino acid sequence and, hence, activity of the protein • Natural selection may favor one allele over another

  28. Fig. 8.11 The journey from DNA to phenotype

  29. Fig. 8.11 The journey from DNA to phenotype

  30. Why Some Traits Don’t Show Mendelian Inheritance • Mendelian segregation of alleles can be disguised by a variety of factors • Complete dominance • Incomplete dominance • Codominance • Sex-linked • Environmental effects • Continuous variation • Epistasis

  31. DIFFERENT TYPES OF DOMINANCE COMPLETE DOMINANCE- a heterozygous & a homozygous dominant organism are the same phenotypically. i.e BB=Bb

  32. COMPLETE DOMINANCE B=brown eyes b=blue eyes BB x bb B B All offspring will be…? b Bb b

  33. INCOMPLETE DOMINANCE- 2 or more alleles influence the phenotype resulting in a phenotype intermediate of the dominant and the recessive trait. + =

  34. Incomplete Dominance

  35. INCOMPLETE DOMINANCE FBFB x FBFR FB= blue fur FR= red fur WHAT ARE THE POTENTIALOFFSPRING’S PHENOTYPES?? FB FB FBFB FBFB FB BLUE FURRED PURPLE FURRED FR FBFR FBFR

  36. CODOMINANCE- neither of the 2 alleles of the same gene totally masks the other. The result is a combination of both dominant traits.

  37. CODOMINANCE R = red colored coat W= white colored coat RR x WW R R All offspring will be …..? RW RW W RED & WHITE !! W RW RW

  38. Blood Types There are 6 genotypes. They make up 4 phenotypes (blood types). A and B are codominant, and O is recessive. A A B B AB O

  39. What are the possible blood types of the potential children of an AB (IAIB) male and an B (IB i) female? What % chance will the offspring be type B? Hint: use a punnett square

  40. What are the possible blood types of the potential children of anAB (IAIB)male and anB (IB i)female? IAIB x IBi IA IB TYPES: A, B, or AB IB What % chance will the offspring be type B? i 50%

  41. SEX LINKED TRAITS THESE ARE TRAITS LOCATED ON THE SEX CHROMOSOMES. MALES PASS GENES LOCATED ON THE “X” CHROMOSOME TO ALL OF THEIR DAUGHTERS & NONE OF THEIR SONS. WHATEVER MOM HAS ON HER “X” CHROMOSOME WILL BE EXPRESSED IN HER SONS EVEN IF THE TRAIT IS RECESSIVE.

  42. SEX LINKED ( X-LINKED) H= non hemophilia h= hemophilia XhXh x XHY Xh Xh XH Y WHAT ARE THE CHANCES OF HAVING A MALE WITH HEMOPHILIA? 100%

  43. SEX INFLUENCED TRAITS THE PRESENCE OF MALE OR FEMALE HORMONES INFLUENCES THE EXPRESSION OF CERTAIN TRAITS. EX: PATTERN BALDNESS IF FEMALE IS HETEROZYGOUS SHE WILL NOT BE BALD. -the gene is recessive in females IF A MALE IS HETEROZYGOUS HE WILL BE BALD. -the gene is dominant in males

  44. ENVIRONMENTAL EFFECTS Many alleles are expressed depending on the environment. Some are heat sensitive Ex:Arctic foxes make fur pigment only when the weather is warm.

  45. CAN YOU SEE WHY THIS TRAIT WOULD BE AN ADVANTAGE?

  46. Continuous Variation • Most traits are polygenic • They result from the action of more than one gene • These genes contribute in a cumulative way to the phenotype • The result is a gradation in phenotypes or continuous variation Extremes are much rarer than the intermediate values

  47. EPISTASIS INTERACTION BETWEEN THE PRODUCTS OF TWO GENES IN WHICH ONE OF THE GENES MODIFIES THE PHENOTYPIC EXPRESSION PRODUCED BY THE OTHER. EX: COAT COLOR FOR LABRADOR RETRIEVERS.

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