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Genetics

Genetics . Vocabulary. Genetics Vocabulary. Allele - alternative form that a single gene may have for a particular trait ( dominant & recessive ) Dihybrid – a genetic cross to examine the possible inheritance of two specific alleles (traits) ( e.g. flower color & plant height )

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Genetics

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  1. Genetics Vocabulary C12L03C12

  2. Genetics Vocabulary • Allele - alternative form that a single gene may have for a particular trait (dominant & recessive) • Dihybrid – a genetic cross to examine the possible inheritance of two specific alleles (traits) (e.g. flower color & plant height) • Dominant - stronger of two genes expressed in the hybrid; represented by a capital letter (R). Masks recessive alleles. • Codominance – Pattern where phenotypes of both homozygous parents are produced in heterozygous offspring so that both alleles for a gene are equally expressed. (e.g. a cross between a red cow (RR) and a white cow (WW) produce red a white (RW) spotted cows)

  3. Genetics Vocabulary • F1 generation - the first-generation offspring in a breeding experiment. (1st filial generation, your parents) • F2 generation - the second-generation offspring in a breeding experiment. (2nd filial generation, you) • Gene - a unit of heredity; a sequence of DNA nucleotides that determines a single characteristic. • Genetics - science of heredity

  4. Genetics Vocabulary • Genotype – gene or allele combination for a trait. This is the letter combination for the genes. (e.g. RR, Rr, rr) • Heredity - passing of traits from parent to offspring • Heterozygous or Hybrid - gene combination of one dominant & one recessive allele     (e.g. Rr) • Homozygous or true breeding (pure) -gene combination involving 2 dominant or 2 recessive genes (e.g. RR or rr)

  5. Genetics Vocabulary • Incomplete Dominance – Pattern where one allele is not completely dominant over the other. Generally displays a new trait. (Parents = Red Flower (RR), and White Flower (rr); Offspring are all Rr with Pink flowers) • Law of Independent Assortment - Mendelian law stating that a random distribution of alleles occurs during the formation of gametes. • Law of Segregation - Mendelian law stating that two alleles for each trait separate during meiosis • Monohybrid – a genetic cross involving a single trait e.g. flower color

  6. Genetics Vocabulary • Parental P1 Generation - the parental generation in a breeding experiment.(your grandparents) • Pedigree – Graphic representation of genetic inheritance used by geneticists to map genetic traits. • Phenotype – Physical expression of the gene. The observable characteristic that is expressed as a result of genotype (e.g. red, white) • Polygenic Traits – traits controlled by two or more genes; genes may be on the same or different chromosomes

  7. Genetics Vocabulary • Punnett Square - a diagram used to analyze the possible gene combinations of the offspring between two individuals. ( genotypes and phenotypes) • Recessive - gene that shows up less often in a cross; represented by a lowercase letter (r). Is not seen if a dominant allele is present. • Sex Linked Traits – traits controlled by genes located on sex chromosomes ( X and Y chromosomes) • Trait — characteristic that is inherited; can be either dominant or recessive

  8. Genetics Mendelian Genetics

  9. Gregor Johann Mendel(1822 -1884) • Known as the “father of genetics” • Austrian Monk • Studied the inheritance of traits in pea plants • Developed the rule of dominance and laws of inheritance • Mendel's work was not recognized until the turn of the 20th century

  10. Why Peas, Pisumsativum? • Can be grown in a small area • Produce lots of offspring very quickly • Produce pure plants when allowed to self-pollinate several generations • Can be artificially cross – pollinated

  11. Eight Pea Plant Traits

  12. Eight Pea Plant Traits • Seed shape--- Round(R)orWrinkled(r) • Seed Color---- Yellow(Y)orGreen(y) • Pod Shape--- Smooth(S)orWrinkled(s) • Pod Color---  Green(G)orYellow(g) • Seed Coat Color---Gray(G)orWhite(g) • Flower position ---Axial(A)orTerminal(a) • Plant Height--- Tall(T)orShort(t) • Flower color --- Purple(P) orwhite(p) He studied only one trait at a time to control variables, and he analyzed his data mathematically.

  13. Reproduction in Flowers stamen • Pollen contains sperm which is produced by the stamen • Ovary (found inside the flower) contains eggs pistol ovary • Pollen carries sperm to the eggs for fertilization • Self-fertilization can occur in the same flower • Cross-fertilizationcan occur between flowers

  14. Mendel’s Experiments • Mendel cross-pollinated flowers using a paintbrush • He could snip the stamens to prevent self-pollination • He traced traits through the several generations

  15. Mendel’s Experiment Mendel produced pure strains by allowing the plants to self-pollinate for several generations

  16. Mendel’s Monohybrid Cross Mendel’s first experiments are called monohybrid crosses because mono means “one” and the two parent plants differed from each other by a single trait like height

  17. Punnett Squares Used to help solve genetic problems

  18. Punnet Squares • When recording the results of crosses, it is customary to use the same letter for different alleles of the same gene. • An uppercase letter is used for the dominant allele and a lowercase letter for the recessive allele. • The dominant allele is always written first. Tall plant Short plant t t T T T t T t

  19. Generations (P1 generation; both true breed) Mendel cross-pollinated a tall pea plant with pollen from a short pea plant Tall pea plant T T t Short pea plant t

  20. Generations (F1 generation) All of their offspring were as tall or taller than the parent plants. Tall pea plant T T Tt Tt t Short pea plant Tt Tt t

  21. Generations (F1 generation) These plants were allowed to self pollinate Tall pea plant T t Tall pea plant T t

  22. Generations (F2 generation) Three-fourths of the plants were as tall as the tall plants in the parent and first generations and One-fourth of the offspring were as short as the short plants in the parent generation. Tall pea plant T t T T T T t Tall pea plant t T t tt

  23. Generations Summary • Parent generation (P1) produced all tall pea plants. (F1) • Short phenotype disappeared • First generation (F1) • A cross of two offspring from P1 • Produce F2 • Second generation (F2) • Short phenotype reappears P1 Short pea plant Tall pea plant F1 All tall pea plants F2 3 tall: 1 short

  24. Mendel’s Conclusions • In every case, he found that one trait of a pair seemed to disappear in the F1 generation, only to reappear unchanged in one-fourth of the F2 plants. • Mendel concluded that each organism has two factors that control each of its traits. • We now know that these factors are genes and that they are located on chromosomes.

  25. The Rule of Dominance • An organism’s two alleles are located on different copies of a chromosome—one inherited from the female parent and one from the male parent. • Mendel called the observed trait dominant and the trait that disappeared recessive.

  26. Mendel’s Laws of Inheritance Mendel’s experiments helped him formulate the 2 laws of inheritance. • The law of segregation And 2. The law of independent assortment

  27. Law of Segregation States that every individual has two alleles of each gene and when gametes are produced, each gamete receives one of these alleles. • During the formation of gametes (eggs or sperm), the two alleles responsible for a trait separate from each other. • Alleles for a trait are then "recombined" at fertilization, producing the genotype for the traits of the offspring.

  28. Applying the Law of Segregation Female Parent Tt Male Parent T t Female Gametes TT Tt T Tt Tt tt t Male Gametes

  29. An Example: Your mother has the recessive gene for a unibrow (uu), Your father has the dominant gene for two eyebrows (UU) DAD MOM YOU Genotype: Uu Phenotype: two eyebrows

  30. Law of Independent Assortment • States that genes (traits) for different traits—for example, seed shape and seed color—are inherited independently of each other. • This law can be illustrated using dihybrid crosses.

  31. Genetics Monohybrid Crosses

  32. Genotypes VS. Phenotypes Genotype Possibilities: RR,Rr,rr Phenotype Possibilities: Redor White Red(R) Dominant – White (r)Recessive

  33. P1 Monohybrid Cross • Trait: Seed Shape • Alleles:R– Roundr – Wrinkled • Cross: Round seeds x Wrinkledseeds RR x rr Genotype:Rr Phenotype: Round GenotypicRatio:All alike PhenotypicRatio: All alike r r Rr Rr R R Rr Rr

  34. P1 Monohybrid Cross Review • Homozygous dominant X Homozygous recessive • Offspring all Heterozygous (hybrids) • Offspring called F1 generation • Genotypic & Phenotypic ratio is ALL ALIKE

  35. F1 Monohybrid Cross • Trait: Seed Shape • Alleles:R– Roundr – Wrinkled • Cross:Roundseeds xRoundseeds Rr xRr Genotype:RR, Rr, rr Phenotype: Round & wrinkled G.Ratio:1:2:1 P.Ratio:3:1 R r RR Rr R r Rr rr

  36. F1 Monohybrid Cross Review • Heterozygous X Heterozygous • Offspring:25% Homozygous dominant RR50% HeterozygousRr25% Homozygous Recessive rr • Offspring called F2 generation • Genotypic ratio is 1:2:1 • Phenotypic Ratio is 3:1

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