1 / 26

INTRODUCTION TO LINKED GENES AND SEX LINKAGE H. Biology/ Ms. Kim

INTRODUCTION TO LINKED GENES AND SEX LINKAGE H. Biology/ Ms. Kim. Figure 15.1. Locating Genes on Chromosomes. Genes Are located on chromosomes Code for protein that determines specific traits. Gene Linkage. Linked genes

dolan
Download Presentation

INTRODUCTION TO LINKED GENES AND SEX LINKAGE H. Biology/ Ms. Kim

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. INTRODUCTION TO LINKED GENES AND SEX LINKAGE H. Biology/ Ms. Kim

  2. Figure 15.1 Locating Genes on Chromosomes • Genes • Are located on chromosomes • Code for protein that determines specific traits.

  3. Gene Linkage • Linked genes • Usually inherited together because located near each other on the SAME chromosome • Genes closer together on the same chromosome are more often inherited together • Each chromosome • Has 100’s or 1000’s of genes • Sex-linked genes exhibit unique patterns of inheritance; genes linked on the X or Y chromosome

  4. What is gene linkage? • Thomas Hunt Morgan (1910) noticed that eye color in fruit flies and wing size always seemed to be inherited together in offspring. • This seemed to go against Mendel’s Law of Independent Assortment • Morgan discovered chromosomes are a group of linked genes • Law of Independent Assortment was still true, but chromosomes assort independently, not genes.

  5. Gene Linkage • Genes located on the same chromosome will NOT sort independently • They will be inherited together • Gene Linkage: • Tendency of 2 alleles (for different traits) to be inherited together • The closer the genes are, the more likely they are to be inherited together

  6. Mendel’s Principle of Independent Assortment? • Remember: this refers to genes on separate chromosomes Gene 1 Gene 2

  7. What would cause genes on the same chromosome to be inherited separately? • Crossing over!

  8. What is gene mapping? Location of Gene on a chromosome is it’s LOCUS

  9. Morgan’s Discovery: Sex Linked Traits • Eye color is linked on X Chromosome • Females carry 2 copies of gene; males have only 1 copy • If mutant allele is recessive, white eyed female has the trait on both X’s • White eyed male can not hide the trait since he has only one X.

  10. How is Sex Determined? • Male can give either an X or a Y • Females can only give an X MALE X Y XX WHAT IS THE PROBABILITY OF HAVING A MALE OR A FEMALE OFFSPRING? X X FEMALE

  11. Sex Determination

  12. What is a sex-linked gene? • Sex- Linked Gene: • Any gene that resides on a sex chromosome • X-linked- gene resides on X chromosome • Y- linked – gene resides on Y chromosome In humans: - Most sex-linked genes are on the X chromosome - Since, typically the X chromosome is longer, it bears a lot of genes not found on the Y chromosome (Usually on X chromosome called x-linked)

  13. What is a sex-linked gene? The "a" recessive allele will be The "a" recessive allele will notexpressed in his phenotypebe expressed in her phenotype

  14. What is a sex-linked gene? (Y-LINKED) • Genes on the Y chromosome can only be passed to sons. NOT to daughters. FEMALE X X MALE YaX

  15. What is a sex-linked gene? (X-LINKED) Genes on the X chromosome can be passed to either sons or daughters. • Females can be homozygous or heterozygous. • Males are hemizygous. What is the probability of having a son with recessive phenotype? Daughter? FEMALE XAXa MALE XAY

  16. Sex-Linked Traits Practice R=Red eyes r=white eyes • What will the phenotypes be for the following fruit flies? • XRXR • XrXr • XRXr • XRY • XrY

  17. Sex-Linked Traits Practice • White eyes (recessive) are very rare compared to red (dominant) eyes in fruit flies • Eye color is located on the X chromosome • Cross a red eyed female (XRXR) with a white eyed male (XrY) • Now, cross a female and male from the possible offspring produced in earlier cross.

  18. Sex-Linked Traits Question If certain recessive disorders, such as color blindness and hemophilia, are sex-linked on the X chromosome, are they more common in males or females? Explain

  19. SEX-LINKED TRAITSWhy are males more often affected by hemophilia? Men only have one copy of the X chromosome. If a male inherits a mutated gene on the X chromosome, the trait is expressed. Females have two copies of the X chromosomes, so the mutated gene may be masked by a normal gene copy.

  20. How is colorblindness a sex-linked trait? • Red-green colorblindness is caused by light-sensitive cells (cones) in the eyes that aren’t working properly • Individuals who are affected can’t distinguish reds from greens

  21. Regular Vision Colorblind

  22. What are Sex-linked Disorders? • Usually inherited as sex-linked recessive traits. • Males need only to inherit one recessive allele to have disorder (XaY) • Females must inherit two recessive alleles to have disorder ( 1 from mother, 1 from father) (XaXa)

  23. Pedigree for Colorblindness in a family What genotype is our 2nd generation female “?” XB X? XB Y She MUST be XBXB Otherwise, her son would be colorblind!

More Related