2 Pre-Mendel’s Theories Blending Hypothesis: when parents with different traits have offspring, they will always show a blending of the traitsSpontaneous generation: Non-living matter giving rise to living matterHomunculus: The little man inside the sperm
4 Mendel’s experiments with pea plants Particulate hypothesis: Parents pass on to their offspring separate and distinct factors (genes) that are responsible for inherited traitsGene: factors pass on from parents to offspring. Sequence of DNA that determines a traitTrait: a specific characteristic of an individualGenetics: the study of heredity
13 Genus species (organism) NUMBER OF CHROMOSOMES Homo sapiens (human)______________________________46Mus musculus (house mouse)_________________________40Drosophila melanogaster (fruit fly)_____________________8Caenorhabditis elegans (microscopic roundworm)_________12Saccharomyces cerevisiae (budding yeast) ______________32Arabidopsis thaliana (plant in the mustard family) ________10Xenopus laevis (South African clawed frog)______________36Canis familiaris (domestic dog)________________________78Gallus gallus (chicken) ______________________________28Zea mays (corn or maize)____________________________20Muntiacus reevesi (the Chinese muntjac, a deer) _________23Muntiacus muntjac (its native american cousin) __________6Myrmecia pilosula (an ant) ___________________________2Parascaris equorum var. univalens (parasitic roundworm)___2Cambarus clarkii (crayfish)___________________________200Equisetum arvense (field horsetail, a plant)______________216
15 Mendel’s principle of segregation There are alternative forms of factors (genes) called alleles.For each character, an organism has two alleles for the gene controlling that character, one from each parent. Homozygous = same alleles Heterozygous = different alleles
16 Principle of segregation (cont.) When only one of the two different alleles in an heterozygous individual appears to affect the trait, that allele is called the dominant allele. The allele that does not appear to affect the trait is called the recessive alleleThe two alleles for a character segregate (separate) during the formation of gametes (sex cells). Each gamete carries only one allele of each character (Principle of segregation)
17 Phenotype refers to the observable trait (purple flowers) Genotype refers to the combination of alleles (PP)Phenotypic ratio: ratio of plants with purple flowers to those with white flowers (3 purple : 1 white)Genotypic ratio: ratio of possible combinations of alleles (1 PP : 2 Pp : 1 pp)
18 Phenotype refers to the observable trait (purple flowers) Genotype refers to the combination of alleles (Pp)
19 Phenotypic ratio: ratio of plants with purple flowers to those with white flowers (3 purple : 1 white)Genotypic ratio: ratio of possible combinations of alleles (1 PP : 2 Pp : 1 pp)
20 Probability and Punnett Squares Punnett Square: Diagramused to show the probabilityof a genetic crossProbability: Chance ofSomething happening
21 How can you find out the genotype of an individual showing the dominant trait?
22 TESTCROSSIn a testcross, an individual of unknown genotype, but dominant phenotype is crossed with a homozygous recessive individual
28 Principle of Independent Assortment During gamete formation in an F2 cross, a particular allele for one character can be paired with either allele of another character
29 Intermediate or incomplete inheritance Codominance Multiple alleles Not all traits are inherited following the patterns found by Mendel in pea plantsIntermediate or incomplete inheritanceCodominanceMultiple allelesPolygenic inheritanceEnvironment - Epigenetics_dominance.html
30 Intermediate or Incomplete Inheritance The heterozygotes have a phenotype that is intermediate between the phenotypes of the two homozygotes
31 condition in which both alleles for a gene are expressed when present (cattle: red, white, roan coat = codominant)Codominance
32 Genetic Determination of Blood Type Multiple Alleles -Genetic Determination of Blood TypeFor many genes several alleles exist in the population.Multiple alleles control the character of blood type in humans.There are six possible genotypes.The alleles IA and IB exhibit codominance, meaning that a heterozygote expresses both traits.Phenotype(Blood type)GenotypesOiiAIA IA or IA iBIB IB or IB iABIA IB
41 Morgan's monohybrid cross for fly eye color produced a 3 : 1 phenotypic ratio of red to white eyes in the F2 generation. However, none of the flies with white eyes were female.
42 Chromosome Theory of Inheritance Genes are located on chromosomesBehavior of chromosomes during meiosis and fertilization accounts for inheritance patterns – chromosomes undergo segregation and independent assortment during meiosis
44 Gene locus: location at which alleles of a gene reside on homologous chromosomes Linked genes: genes that are located in the same region of a chromosomeGenetic linkage: tendency for the alleles on one chromosome to be inherited together. The closer two genes are on a chromosome, the greater the genetic linkage
46 MeiosisOrganisms that reproduce sexually have specialized cells called gametes (sex cells)Gametes are the result of a type of cell division called meiosis
47 Diploid and haploidAlmost all human cells are diploid or containing two homologous sets of chromosomes2n = 46Eggs and sperm cells (gametes) are haploid or containing a single set of chromosomesn = 23
52 haploid egg and spermdiploid zygoteIn the human life cycle a haploid egg and sperm fuse and form a diploid zygote. Mitosis produces an embryo with numerous cells that continue to multiply and develop.
59 MITOSIS MEIOSIS TYPE OF CELL (that undergoes this division) (pages 195, 200, & 201)MITOSISMEIOSISTYPE OF CELL (that undergoes this division)# OF CELL DIVISIONSStarts/ends as diploid or haploid cell# OF DAUGHTER CELLS# OF CHROMOSOMES AFTER DIVISIONEXCHANGE OF DNA (Y/N)UNIQUE OR IDENTICAL CELL AFTER DIVISION