Presentation on theme: "Chapter 11 Introduction to Genetics"— Presentation transcript:
1 Chapter 11 Introduction to Genetics Gregor Mendel
2 A brief history Gregor Mendel Breeding experiments using garden peas (1850s)Established basic principles of heredityFather of genetics
3 Basic vocabulary 1) Dominant 2) Recessive 3) Alleles Trait that is expressed (by covering another)2) RecessiveTrait that is hidden (may be covered by another)3) AllelesAll genes for a specific trait
4 Dominant and recessive traits The traits that seem to mask other traits when present are called dominant traits.The traits that seem to be hidden in the presence of dominant traits are called recessive traits.
5 5) Heterozygous (hybrid) 4) Homozygous (pure)Both genes for a trait are the same5) Heterozygous (hybrid)Both genes for a trait are different
6 Homozygous vs. Heterozygous Homozygous: inheriting two of the same alleles for a trait (AA tall/tall or aa short/short)Allele: a variety of a traitHeterozygous: inheriting different allele for a trait (Aa, tall/short)Mendel concluded that each trait has two alleles that determines its appearance.
7 Phenotype? Genotype? 6) Phenotype Actual expression of a gene (words describing)7) GenotypeActual genes present (symbols used)Phenotype?Red or WhiteGenotype?RR or Rr or rr
8 8) Mendel’s crosses: P = original parents F1 = first filial (offspring) of parentsF2 = second filial (offspring of F1)
9 What did Mendel observe? When a true-breeding (homozygous) tall plant is crossed with a true-breeding short plant in the P generation, the F1 height trait is always predictable. 100% are tall plants.P generation F F2
10 Law of SegregationMendel concluded only one allele is passed from parent to offspring for each trait.F1 plants must be heterozygous because the P generation only passed on one tall allele and one short allele.The F1 plant will then pass on to its offspring either a tall or a short allele, never both.
11 What happens when the F1 tall plants are crossed together? Mendel observed that the F2 generation, the offspring of F1 plants, are always in a fixed ratio of 3:1 tall:short.Why?P generation F F2
12 9) Punnett SquaresMathematical grid showing probable or possible offspring from a cross (phenotype & genotype ratios)Monohybrid cross = working with only one trait
13 Punnett square Tt x TtPunnett created a table to show the average inheritance pattern of one offspring.
14 Pea traits that Mendel identified Through multiple crosses, Mendel determined that all these traits displayed a mathematical predictability for inheritance.Seed ShapeSeed ColorSeed CoatColorPodShapePod ColorFlower PositionPlant HeightRoundYellowGraySmoothGreenAxialTallWrinkledGreenWhiteConstrictedYellowTerminalShortRoundYellowGraySmoothGreenAxialTall
15 Law of independent assortment Because organisms are made up of more than one trait, Mendel concluded that the inheritance of one trait does not influence the inheritance of a second trait.Example: Height of the pea plant does not influence the color of the peasHeight is independently assorted from color.
16 10) Dihybrid crossworking with two traits (gives twice as many gametes possibilities, so 4 times as many offspring) classical ratio of 9:3:3:1
17 Using dihybrid crosses to show independent assortment A smooth, yellow pea (RrYy) can pass on these combinations of genes to its offspring: RY, Ry, rY, or ry.
19 11) incomplete dominance Both alleles for a trait blend together creating a new expression in the heterozygous conditionexamples: snapdragons
20 Variations on MendelIncomplete dominance: the heterozygous genotype shows a blend of the two parents and not the dominant allele
21 12) co-dominance Both alleles for a trait show up equally Examples: roans, “checkered” chickens
22 Variations on MendelCodominance: the heterozygous genotype shows both inherited allelesExample of roan horse coat: AA (dark red) x aa (white) Aa (dark red and white)
23 13) multiple alleles More than two alleles for a trait Examples: coat color of rabbitsKeyC = full colorCch = chinchillaCh = HimalayanC = albinoCC, Ccch, Cch, or Cccchch, cchcch, or cchcchc or chchcc
24 Variations on MendelMultiple alleles: when there are more than two alleles that code for a traitExample: ABO blood typeA type = AA or AoB type = BB or BoO type = ooAB type = AB
29 Modernizing Mendelian genetics DNA is the basis for inheritance.DNA are coiled into chromosomes.Parts of the DNA that code for a trait are called genes.Some genes have only two alleles and other have more.Gene for hairline Allele: AGenotype: AaGene for hairline Allele: a
30 Homologous Chromosomes. (homologues) Chromosome pairs or mates (similar in size, shape, info)0ne from each parentHumans have 23 pair (total = 46)
31 MeiosisA process of reduction division in which the number of chromosomes per cell is cut in half through the separation of homologous chromosomes in a diploid cell.Meiosis usually involves two distinct divisions, called meiosis I and meiosis II. By the end of meiosis II, the diploid (2n) cell that entered meiosis has become four haploid (n) cells.
32 Meiosis Production of haploid gametes Similarities to Mitosis: Same basic stages, except occur twice
33 Gametes Haploid (n or 1n) Reproductive cells (eggs & sperm) A cell with one of each type of chromosome or half the total number
34 Result is “reduction division” into 4 haploid cells instead of 2 diploids In males = all 4 become spermIn females = only 1 egg; other “polar bodies” disintegrate
36 Meiosis II Prophase II Metaphase II Anaphase II Telophase II Meiosis I results in two haploid (N) daughter cells, each with half the number of chromosomes as the original.The chromosomes line up in a similar way to the metaphase stage of mitosis.The sister chromatids separate and move toward opposite ends of the cell.Meiosis II results in four haploid (N) daughter cells.
37 Zygote(fertilized egg) first cell of an organism with a complete set of chromosomesDiploid (2n)Cell with a full set (two of each type) of chromosomes
38 Oocyte or Spermatocyte (egg cell) (sperm cell) This cell that can undergo meiosis originally has 6 chromosomes and has replicated to 12 chromosomes in preparation for meiosis.
39 Differences: Homologues remain together during prophase I Crossing over (when chromatids exchange pieces) occurs during metaphase I
57 Variations on MendelLinked genes: Mendel concluded that traits are assorted independently, but some traits are linked.This means that two genes are almost always inherited together (ex: red hair, green eyes).
58 Fruit fly chromosome #2Exact location on chromosomesChromosome 2For example, a fly with reddish-orange eyes andminiature wings, were almost always linked, inherited,together.