html5-img
1 / 20

General Genetics

General Genetics. Chapter 14 Mendel and the Gene Idea. Objectives. Understand Mendels three Laws governing genetics Understand the meaning of the relevant vocabulary discussed in class Be able to predict the results of a mono & dihybrid cross using a Punnett square

crevan
Télécharger la présentation

General Genetics

An Image/Link below is provided (as is) to download presentation Download Policy: Content on the Website is provided to you AS IS for your information and personal use and may not be sold / licensed / shared on other websites without getting consent from its author. Content is provided to you AS IS for your information and personal use only. Download presentation by click this link. While downloading, if for some reason you are not able to download a presentation, the publisher may have deleted the file from their server. During download, if you can't get a presentation, the file might be deleted by the publisher.

E N D

Presentation Transcript

  1. General Genetics Chapter 14 Mendel and the Gene Idea

  2. Objectives • Understand Mendels three Laws governing genetics • Understand the meaning of the relevant vocabulary discussed in class • Be able to predict the results of a mono & dihybrid cross using a Punnett square • Be familiar with patterns of inheritance for genes on sex chromosomes • Understand the concept of “Linked Genes” • Understand how recombination of genes affect genetic variability • Be familiar with special situations regarding genotype/phenotype predictions

  3. The physical appearance of an organism reflects its genetic makeup Each gene codes for a different polypeptide Polypeptide combinations may alter the appearance of an organism Gene (Character): is a feature that is heritable Locus: specific area on chromosome where the gene is found Allele (Trait): is a variation of a character Genotype: the genetic makeup of an organism (combination of genes in its nucleus) Phenotype: the physical appearance of an organism Descriptors

  4. Gregor Mendel described three Laws of Genetics Law of Segregation: each parent has two copies of a gene but only one is passed to the offspring via the gametes (separation of homologous pairs) Three possible genotypes for each gene in the diploid cell Homozygous dominant: both alleles of a gene are of the “Dominant” variety Homozygous recessive: both alleles of a gene are of the “Recessive” variety Heterozygous: the diploid cell has one dominant and one recessive allele for each gene Mendelian Genetics

  5. Law of Independent Assortment: genes residing on different chromosomes separate without regard for one another • describes the broad range of variation seen in organisms • Law of Dominance: some alleles for a gene are fully expressed if present (dominant) in the phenotype while others have no affect (recessive) • hierarchy of alleles

  6. Genetics is Probability • In a diploid organism (2n), each allele has a 50:50 chance of being found in a particular gamete (1/2). • To calculate the likelyhood of two alleles recombining during fertilization, we must multiply our probability for each allele together (1/2 x 1/2 = 1/4)

  7. Punnett Square • Device used to predict potential genotypes of offspring • Along each axis are placed the gamete possibilities for each parent • Internal boxes represent union of genotypes for offspring produced by the union of the corresponding axial gametes • Phenotypes can be determined for each potential zygote

  8. Sex Linked Inheritance • Males and females differ in their sex chromosome combination (females XX; males XY) • Barr bodies • Because the X contains genes and the Y “does not”, inheritance patterns of sex-linked genes vary between the sexes • recessive traits more prevalent in males

  9. Concept of Linked Genes • Linked genes are those that reside on the same chromosome and tend to be inherited together • Genes residing on the autosomal chromosomes (pairs 1-22) are said to be autosomal genes • Sex-linked genes are found on the sex chromosomes (pair 23, usually on the X)

  10. Recombination of Genes • Production of offspring with a new combination of traits is called genetic recombination • Independent assortment may recombine genes that are unlinked • Linked genes can become unlinked through recombination events like crossover (during meiosis)

  11. Gene Mapping • Maps of genes on chromosomes can be constructed from recombination data • Recombination data for linked genes reflects the “distance” of the 2 loci from one another • The farther apart 2 loci are from one another the more frequent the observed recombination due to crossover Linkage map: genetic map based on recombination frequencies

  12. Incomplete dominance: the phenotype of a heterozygous genotype is intermediate in appearance Codominance: each allele in the genotype for a particular gene will be expressed in the phenotype Pleiotropy: the ability of a gene to affect an organism in many ways Epistasis: gene at one locus influences the expression of a gene at another locus (different gene) Polygenic Inheritance: additive effect of 2 or more genes on a phenotypic character Special Situations

  13. Incomplete Dominance(heterozygous genotype is intermediate in appearance)

  14. Codominance(each genotypic allele will be expressed)

  15. Pleiotropy(single gene affects multiple phenotypes) • Sickle Cell Disease • Production of abnormal hemoglobin • Prevalent amongst African Americans, but rare in people of other races

  16. Epistasis(one gene influences the expression of another gene)

  17. Polygenic Inheritance(additive effect of 2 or more genes on a phenotypic character)

More Related