Introduction to Genetics Notes CH 11 Go to Section:
Introductory Vocabulary 1.Trait: observable, inheritable characteristic eye color. Example of traits in pea plants: Plant height, flower color, seed color, seed shape 2. Gene: region of a chromosome that controls a particular trait CharacterTraits HeightTall or Short Flower ColorPurple or White Seed ColorYellow or Green Seed ShapeRound or Wrinkled
3. Allele: a different form of a gene (ex:eyecolor gene: alleles are blue, green, brown…) 4. Pure bred: organism that would produce identical offspring as itself (AA or aa) 5. Hybrid: organism produced by crossing parents with differing traits (Aa or “mix”) 6. Homozygous: Organisms that have 2 identical alleles for a particular trait (AA or aa) 7. Heterozygous: Organisms that have 2 different alleles for a particular trait (Aa) Trait: Stem height Alleles: T (Tall) or t
9. Genotype: genetic makeup (represented by 2 letters) 10. Phenotype: physical characteristics (word used to describe – blue, green, brown) 11. Gametes: sex cells (egg or sperm) 12. Gregor Mendel: in 1843 he became a monk in an Austrian monastery 13. Heredity: passing on characteristics from parent to offspring 14. Genetics: study of heredity
Gregor Mendel: The Father of Genetics 1. Gregor Mendel: 1822-1884 Austrian monk a.Did genetics (breeding) experiments on garden pea plants. b.1866: Published paper on experiments Gregor Mendel
Cut stamens (holds pollen) off of one flower Brushed pollen from a 2 nd flower onto carpel (holds eggs) of 1 st flower Carpel develops into a pea pod. d. Mendel can control the fertilization (pollination) or mating of these plants. Fertilization: the joining of gametes. Two types of fertilization: 1. self-fertilization – the pollen fertilizes the ovule on the same flower 2. cross-fertilization – the pollen of one plant is used fertilize the ovule of another plant.
Conclusions made by Mendel: 1. Each parent MUST contribute one gene for each trait to the offspring. –Evidence: F 2 ’s had white flowers (present but hidden in F 1 generation.) 2. Each parent must have two copies of a gene; and can have two different versions of that gene called alleles at the same time. -- Evidence: F 2 ’s had white flowers both parents must have had at least one white allele! Dominant: allele that is expressed when 1 or both are present (capital letter) Recessive: allele that is masked by presence of dominant allele (lower case) a. The individual MUST have both recessive alleles to show the recessive trait Slide # 9 The F 1 purple flowering plants must have a second hidden gene for white flowers!
Alleles 1. Alleles: alternate forms of a gene or trait a. Parents may have two of the same alleles or two different alleles b. Homozygous: having 2 identical alleles c. Heterozygous: having 2 different alleles 2. Alleles are located on chromosomes This plant has 2 different alleles for the flower color character. Slide # 8 Every organism has two copies of the same gene. One copy came from MOM in her egg, the other gene copy came from DAD in his sperm. MOM DAD FROM Homologous Chromosomes
Homologous Chromosomes: -are similar gene carrying chromosomes from the opposite-sex parents.
Mendel Solves the Genetics Puzzle 1.Mendel reasoned that each parent must have 2 possible alleles to contribute –Genotype: the alleles the organism has (two letters) –Phenotype: physical appearance of an organism 2.Mendel reasoned that the two alleles separated when gametes (sex cells like eggs) formed. 3.Mendel also reasoned that the alleles paired up again during fertilization (joining of egg &sperm) Genotypes: PP x pp Gametes: P ~ p Fertilization: Pp Genotype of F1: All Pp Slide # 10 Phenotype of F1: All Purple Phenotypes: Purple & White Purebred Hybrid
Gene Diagram – Flower color Alleles- P = Purple flower p = White flower All genes occur in pairs – so 2 alleles affect a characteristic – possible combinations are; genotypes PP Pppp PhenotypesPURPLE PURPLE WHITE
1. Determine what the alleles are. P=purple p=white 2.Parent genotypes are determined. --Both are Pp 3.Parent’s possible gametes are determined and placed one next to -or above each box. Pp Purple male Pp purple female Pp P p Complete the Cross PP Pp pp 3 purple and 1 white offspring 3:1 chance with these parents Punnett Square