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Genes and Heredity

Genes and Heredity. Biological traits/allele Similarities in appearance Characteristics Explanation of diversity. What are Traits?. The characteristics an organism possesses. Eye Color Hair Color Height Body Structure Facial Features Skin pigmentation. How are traits passed on?.

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Genes and Heredity

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  1. Genes and Heredity Biological traits/allele Similarities in appearance Characteristics Explanation of diversity

  2. What are Traits? The characteristics an organism possesses. • Eye Color • Hair Color • Height • Body Structure • Facial Features • Skin pigmentation

  3. How are traits passed on? • When organisms reproduce, traits are passed from parent to offspring. • These traits are carried in DNA, the genetic material found in a cell’s nucleus. • DNA acts like a blueprintor the instructions to createyour characteristics • A section of DNA responsible for a specific trait is known as an Allele. An allele is the two or more forms of the gene.

  4. Genes and Heredity Heredity is the passing of traits from parents to offspring Genes control biological traits • Found on the chromosomes in every cell of the body • Characteristics come from a combination of both parents. • Half of your chromosomes come from your mother, half from your father.

  5. Probability – The odds It is important to know if observed traits are the result of chance, or other factors. If the environment caused the characteristic, then it is not genetic. Collect data and see if the results are due to chance. If a trait is due to genetics then the results will show statistical significance. ***Sample size improves the chances of achieving the expected results and increases our confidence in the results.

  6. Inheritance – Early Beliefs • The idea of inherited traits dates back 6000 years • Evidence of this is seen through stone carvings of pedigrees including horse generations and cross pollination of date palms. • Early records by Chinese farmers show evidence of methods used for improving rice crops. • These ideas were based strictly on observation and trial and error investigation – no isolated experimentation.

  7. Inheritance – Early Beliefs Early naturalists believed: • many organisms came from cross-species mating or hybrids • Giraffe comes form the mating of a camel and a leopard • Crossing traits make a blend • Tall with short parent will produce mid sized offspring

  8. Inheritance – Early Beliefs Many cultures have recognized the value in upholding valued characteristics • Breeding practices for livestock and work dogs. • Seed selection and cross pollination of crops • Intermarriage of upper class and royalty to segregate mating of the elite • Infanticide of the weak or individuals who have undesirable traits

  9. Gregor MendelHeredity meets Science Considered the father of genetics, Gregor Mendel was born in 1822 in Austria. He grew up on his family’s farm and was able to learn a lot about flowers and fruit trees. After going to college, he joined a monastery. At the monastery, he worked in the garden where he studied how traits were passed from parent to offspring.

  10. Gregor MendelHeredity meets Science Mendel noticed that some patterns of inheritance made sense and other did not. For example, Mendel noticed that when he crossed a purple flowered pea plant with a white flowered pea plant, that all of the offspring had purple flowers. He then noticed that if he crossed two of these offspring, then one out of every four offspring had white flowers. Mendel wanted to know why.

  11. Gregor MendelHeredity meets Science • In addition to flower colour, Mendel observed that the garden peas were either green or yellow and were also either round or wrinkled. • He noticed difference in plant heights as all were either tall or short with none in between • There was also variance in flower position on the stem • He felt these traits were significant and began experimentation on them.

  12. Gregor MendelHeredity meets Science • Mendel observed seven traits in the peas that seemed to show consistent patterns including seed shape, seed colour, flower colour, pod shape, pod colour, flower position and plant height. • He intentionally fertilized plants by cross pollination by removing the stamen from one plant and transferring the pollen to the pistil of another plant.

  13. Gregor MendelHeredity meets Science • Tall plants with short plants made tall offspring. (recall early belief of crossing making a blend – not so!) • Purple flowered plants with white flowered plants made purple flowered offspring. • Round seed with wrinkled seeds made round seeds. • Yellow seeds with green seeds made yellow offspring

  14. Gregor MendelHeredity meets Science Mendel concluded that there must be “factors” that were later identified as genes that are passed on that are more dominant than others. Dominant genes determine the expression of the genetic trait in offspring Recessive genes are overruled by dominant genes but are expressed if no dominant gene is present.

  15. 1. Law of Unit Characters Inherited characteristics are controlled by factors that occur in pairs. During cross fertilization, each parent contributes one of these factors. round wrinkled RR rr R R r r Offspring Mendel's Laws of Heredity

  16. 2. Law of Segregation The pair of factors separate or segregate during the formation of sex cells round wrinkled RR rr R Rsex cells form r r Offspring Mendel's Laws of Heredity

  17. 3. Law of Dominance One factor can mask the effect of another if it is dominant. The dominant gene is always indicated by a capital letter (R) a lower case letter (r) is used for the recessive trait round wrinkled RR rr R R sex cells form r r Rr Offspring all round Mendel's Laws of Heredity

  18. Mendel's Laws of Heredity Mendel’s Law of Segregation

  19. 4. Law of Independent Assortment Factors are separated and distributed completely independently of all other factor pairs. round wrinkled yellow pea green pea RR rr YY yy R R sex cells form r r Y Y y y Offspring Offspring all round (Rr) all yellow (Yy) Mendel's Laws of Heredity

  20. A typical Mendelian Cross Parents tall x short P TT tt T T t t First generation F1 Tt Tt Tt Tt all tall

  21. A typical Mendelian Cross F1 Cross tall x tall F1 Tt Tt T t T t second generation F2 TT Tt Tt tt ¾ Tall ¼ short

  22. Punnett Square • In 1910, Reginald C. Punnett devised a way to organize genetic cross studies. • The Punnett Square is a diagram that is used to predict the probability of an offspring having a particular genotype in a particular cross or breeding experiment. • It is a summary of every possible combination of one maternal allelewith one paternal allele for each gene being studied in the cross.

  23. Possible gametes Possible gametes Punnett Square Using Mendel’s Crosses Parents: TT x tt F1 cross: Tt x Tt }{ TT Tt Tt tt Probable offspring F1 are all tall F2 are ¾ tall ¼ short

  24. Punnett Square Solve TT x Tt TT x Tt

  25. Punnett Square Solve TT x Tt TT x Tt

  26. Punnett Square Solve TT x Tt TT x Tt All Tall……. But are they the same?

  27. Solve TT x Tt TT x Tt Phenotype: Description of the trait expressed. ie. tall or short. In this case phenotype is 100% tall. Genotype: The actual gene make up Representation with letters In this case genotype is 50% TT and 50% Tt Describing Alleles

  28. Describing Alleles The genotype can be described using letters or either of the following terms. Homozygous - both of the genes are the same and are considered pure – TT or tt • The recessive phenotype always has the homozygous genotype. Heterozygous - the genes are different and are considered hybrids – Tt

  29. When solving with a Punnett Square, always use the following steps: Define symbols: State the cross Diagram the gametes Complete the squares Summarize the results: and answer the question Punnett Square • T = tall allele • t = short allele • Genotype • Phenotype

  30. Punnett Square • If a short pea plant is crossed with a homozygous tall pea plant, what are the probable offspring? • If a heterozygous purple flowered plant is crossed with a white flowered plant, what are the flower colours of the offspring? • If two round pea plants are crossed and some of the offspring have round seeds while others are wrinkled, what were the genotypes of the parents?

  31. Punnett Square 1. If a short pea plant is crossed with a homozygous tall pea plant, what are the probable offspring? T = Tall tt x TT t = short Phenotype: 100% Tall Genotype: 100% Tt (heterozygous)

  32. Punnett Square 2. If a heterozygous purple flowered plant is crossed with a white flowered plant, what are the flower colours of the offspring? P = Purple Pp x pp p = white Phenotype: 50% purple, 50% white Genotype: 50% Pp (heterozygous) 50% pp (homozygous recessive)

  33. Punnett Square 3. If two round pea plants are crossed and some of the offspring have round seeds while others are wrinkled, what were the genotypes of the parents? R = Round Rr x Rr r = wrinkled Phenotype: 75% round, 25% wrinkled The parents must Genotype: 50% Rr (heterozygous) be heterzygous 25% RR (homozygous dominant) to have both types 25% rr (homozygous recessive) of offspring.

  34. Pedigree Charts • A Pedigree is a chart that shows the genetic relationship between individuals in a family • It can be used to determine whether an allele is dominant, recessive, sex-linked or something else. male without trait male with trait female without trait female with trait • Unless otherwise stated, squares represent males, circles represent females and shaded markers indicate individuals who have the trait

  35. Pedigree Charts Tt Tt T_ Tt tt Tt Tt Tt Likely TT Tt tt Tt tt tt T_ tt T_ Tt • Is the trait dominant or recessive? • Fill in the genotypes wherever possible. The trait must be recessive.

  36. Pedigree Charts ee Ee ee ee E_ Ee Ee ee Ee ee ee Ee ee ee Ee E_ E_ ee E_ • Is the trait dominant or recessive? • Fill in the genotypes wherever possible. The trait must be dominant.

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