1 / 17

Chapter 11 Mendel & The Gene Idea

Chapter 11 Mendel & The Gene Idea. Mendelian genetics. Character heritable feature, i.e., fur color Trait variant for a character, i.e., brown True-bred all offspring of same variety Hybridization crossing of 2 different true-breds P generation parents

munsonm
Télécharger la présentation

Chapter 11 Mendel & The Gene Idea

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. Chapter 11 Mendel & The Gene Idea

  2. Mendelian genetics • Character • heritable feature, i.e., fur color • Trait • variant for a character, i.e., brown • True-bred • all offspring of same variety • Hybridization • crossing of 2 different true-breds • P generation • parents • F1 generation • first filial generation • F2 generation • second filial generation

  3. The Law of Dominance • In a cross of parents that are pure for contrasting traits, only one form of the trait will appear in the next generation. • Offspring that are hybrid for a trait will have only the dominant trait in the phenotype. • When an organism has two different alleles for a trait, the allele that is expressed, overshadowing the expression of the other allele, is said to be dominant. The gene whose expression is overshadowed is said to be recessive. • Mendel’s Law of Dominance

  4. Leading to the Law of Segregation • Alternative versions of genes (alleles) account for variations in inherited characteristics • For each character, an organism inherits 2 alleles, one from each parent • If the two alleles differ, then one, the dominant allele, is fully expressed in the organism’s appearance; the other, the recessive allele, has no noticeable effect on the organism’s appearance • The alleles for each character segregate (separate) during gamete production (meiosis). • Mendel’s Law of Segregation

  5. The Law of Independent Assortment • Law of Segregation involves 1 character. What about 2 (or more) characters? • Monohybrid cross vs. dihybrid cross • The two pairs of alleles segregate independently of each other. • Mendel’s Law of Independent Assortment

  6. Genetic vocabulary……. • Punnett square: predicts the results of a genetic cross between individuals of known genotype • Homozygous: pair of identical alleles for a character • Heterozygous: two different alleles for a gene • Phenotype: an organism’s traits • Genotype: an organism’s genetic makeup • Testcross: breeding of a recessive homozygote X dominate phenotype (but unknown genotype)

  7. Alternative Inheritance Patterns • Incomplete dominance: appearance between the phenotypes of the 2 parents. Ex: snapdragons • Codominance: two alleles affect the phenotype in separate, distinguishable ways. Ex: Tay-Sachs disease • Multiple alleles: more than 2 possible alleles for a gene. Ex: human blood types

  8. Alternative Inheritance Patterns • Pleiotropy: genes with multiple phenotypic effect. Ex: sickle-cell anemia • Epistasis: a gene at one locus (chromosomal location) affects the phenotypic expression of a gene at a second locus. Ex: mice coat color • Polygenic Inheritance: an additive effect of two or more genes on a single phenotypic character Ex: human skin pigmentation and height

  9. Human disorders • The family pedigree • Recessive disorders: • Cystic fibrosis • Tay-Sachs • Sickle-cell • Dominant disorders: • Huntington’s • Testing: • Amniocentesis • chorionic villus sampling (CVS)

  10. Chapter 12 The Chromosomal Basis of Inheritance

  11. Chromosomal Theory of Inheritance • Genes have specific loci on chromosomes and chromosomes undergo segregation and independent assortment

  12. Chromosomal Linkage • Morgan • Drosophilia melanogaster • XX (female) vs. XY (male) • Sex-linkage: genes located on a sex chromosome • Linked genes: genes located on the same chromosome that tend to be inherited together

  13. Genetic Recombination • Crossing over • Genes that DO NOT assort independently of each other • Genetic maps • The further apart 2 genes are, the higher the probability that a crossover will occur between them and therefore the higher the recombination frequency • Linkage maps • Genetic map based on recombination frequencies

  14. Human Sex-Linkage • SRY gene: gene on Y chromosome that triggers the development of testes • Fathers= pass X-linked alleles to all daughters only (but not to sons) • Mothers= pass X-linked alleles to both sons & daughters • Sex-Linked Disorders: Color-blindness; Duchenne muscular dystropy (MD); hemophilia • X-inactivation: 2nd X chromosome in females condenses into a Barr body (e.g., tortoiseshell gene gene in cats)

  15. Chromosomal Errors • Nondisjunction: • members of a pair of homologous chromosomes do not separate properly during meiosis I or sister chromatids fail to separate during meiosis II • Aneuploidy: • chromosome number is abnormal • Monosomy – missing chromosome • Trisomy - extra chromosome (ex. Trisomy 21 Down Syndrome) • Polyploidy - extra sets of chromosomes

  16. Chromosomal Errors • Alterations of chromosomal structure: • Deletion: removal of a chromosomal segment • Duplication: repeats a chromosomal segment • Inversion: segment reversal in a chromosome • Translocation: movement of a chromosomal segment to another

  17. Genomic Imprinting • A parental effect on gene expression • Identical alleles may have different effects on offspring, depending on whether they arrive in the zygote via the ovum or via the sperm. • Fragile X syndrome: higher prevalence of disorder and mental disability in males

More Related