1 / 17

The Chromosomal Basis of Inheritance

The Chromosomal Basis of Inheritance. Chromosomal Theory of Inheritance. Genes are physically located at loci on chromosomes Additionally, it is chromosomes that undergo segregation and independent assortment. Thomas Hunt Morgan.

kendis
Télécharger la présentation

The Chromosomal Basis of Inheritance

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. The Chromosomal Basis of Inheritance

  2. Chromosomal Theory of Inheritance • Genes are physically located at loci on chromosomes • Additionally, it is chromosomes that undergo segregation and independent assortment

  3. Thomas Hunt Morgan • Very important geneticist, studied Drosophila melanogaster (fruit flies) • 8 chromosomes • New generation every 2 wks • XY sex determination

  4. Wild type • He focused on fruit fly eye color • Wild type phenotype: the phenotype that occurs most commonly in a natural population • In fruit flies, red eyes were the wild type (notation for red eyes is w+) • White eyes are considered the mutant phenotype (notation for white eyes is w)

  5. Sex-linked Genes • Genes located on the X chromosome are sex-linked (XY system) • Therefore, males only had 1 allele for eye color

  6. Inheritance of Sex-linked Traits • In humans, males are the heterogametic sex (XY). • Males inherit sex-linked traits from their mother • Males are hemizygous (only 1 allele)

  7. Sex-linked Diseases • Examples of sex-linked genes • Color-blindness • Hemophilia

  8. LINKED GENES • There are many genes located on chromosomes • Genes that are located on the same chromosome tend to be inherited together • These are called LINKED GENES • NOTE: Linked genes do not follow Mendel’s Law of independent assortment

  9. LINKED GENES EXCEPTIONS • Even though genes on the same chromosome are USUALLY inherited together, they are not always. • Think about meiosis . . . • Why do you think that genes on the same chromosome are not always inherited together.

  10. GENETIC MAPPING • ANSWER: Crossing over • Because of the discovery of crossing over, scientists developed a system to map the order of genetic loci, genetic mapping

  11. GENETIC MAPPING • Assumptions: • Crossing over is a random event • Farther apart genes are on the chromosome, the higher the probability that they will be recombined • Therefore: • With enough recombination data, you can map the genes on the chromosome in relation to each other

  12. TYPES OF GENETIC MAPS • Linkage map: a genetic map based on recombination frequencies • Cytogenic map: a genetic map based on staining genes and observing them under the microscope

  13. X-Inactivation • In females, 1 X chromosome in each cell is randomly inactivated and becomes a Barr body

  14. Genomic Imprinting • Most times the expression of the allele is not dependent on which parent donates the trait • PTC taster is dominant (it doesn’t matter if you received the trait from mom or dad) • Sometimes the expression of a trait depends on which parent you receive the trait from . . . Genomic imprinting

  15. Genomic Imprinting • In gametogenesis, some alleles are “silenced” in one parent • Therefore, depending whether the allele is silenced in the sperm or egg, the trait is only active in one gamete (mom’s or dad’s) • Mostly occurs in developmental genes • Individuals heterozygous for a disease on an imprinted allele show different phenotypes depending on which parent it was inherited from

  16. Angelman Syndrome/Prader-Willi • Caused by mutation on chromosome 15 • Angelman: inherited from mother • Jerky movements, Happy disposition, seizures • Prader-Willi – inherited from father • Obesity, learning disabilities, delayed motor development

More Related