1 / 12

Complex Inheritance Patterns

Complex Inheritance Patterns. Sex Determination, Sex-Linked Traits, & Sex Influenced Traits April 17, 2008. Guy or Gal?. Gender is determined by a pair of chromosomes called the sex chromosomes . two types: X and Y – not always homologous females have two X chromosomes

kristen-mccullough
Download Presentation

Complex Inheritance Patterns

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. Complex Inheritance Patterns Sex Determination, Sex-Linked Traits, & Sex Influenced Traits April 17, 2008

  2. Guy or Gal? • Gender is determined by a pair of chromosomes called the sex chromosomes. • two types: X and Y – not always homologous • females have two X chromosomes • males have one X and one Y chromosome • In humans, the remaining 22 pairs of chromosomes are homologous and are referred to as autosomes.

  3. Dosage Compensation • X chromosome is larger than Y • ‘X’ contains 900-1400 genes • ‘Y’ contains fewer than 100 genes – mostly related to “maleness” • In females, one of the X chromosomes is inactivated. • X-inactivation occurs randomly in each body cell. • Form of dosage compensation. • Inactivated X-chromosome condenses into a darkly staining region called a Barr body. • Example: • Calico color in cats Calico cat

  4. Sex-Linked Traits • Traits controlled by genes on the sex chromosomes are called sex-linked traits. • Mostly X-linked traits; very few Y-linked traits. • Males disproportionately affected by recessive alleles on the X chromosome. • Examples: • Red-green color blindness • Hemophilia • Traits located on the autosomes can sometimes be affected by the proportion of sex hormones produced by the body. • Ultimately sex hormone production is prescribed by the sex chromosomes. • These are called sex-influenced traits • Example: • Male pattern baldness

  5. Red-Green Color Blindness Other Colorblindness Tests

  6. Variations in Red-Green Color Blindness

  7. Red-Green Colorblindness • A recessive X-linked trait • Affects 8-12% of males in the United States; less than 0.5% of females. • Results when the color-detecting cones in the retina of the eyes function ‘poorly’ in discriminating between red and green colors. Red-green colorblind vision Normal vision

  8. Color blindness Problem: PROBLEM: • A man with normal vision and a woman who is heterozygous for the colorblind allele want to have a child. • ‘B’ is the allele for normal vision • ‘b’ is the allele for color blindness • What is the probability that their child will be colorblind? • Could they have a colorblind daughter? SOLUTION: • 25% • No, they cannot have a colorblind daughter. The only child that could be affected would be a boy.

  9. Sex-Linked Practice Problem: Hemophilia • A recessive X-linked disorder • Results in a delayed clotting of blood • Will it be more prevalent in males or females? Why? • A man with hemophilia has children with a woman who is a carrier for hemophilia. What is the chance that their next child will have hemophilia? Their next son? Their next daughter?

  10. Sex-Influenced Traits –A Challenge Problem Male pattern baldness is a sex-influenced trait. The gene, B1, for baldness is dominant in males, but recessive in females. The gene, B2, produces normal hair growth in both men and women. The baldness gene is also an autosomal trait. If a man with male pattern baldness and genotype B1B2 marries a woman who is not bald with genotype B2B2, what are the chances that they will have a son with male pattern baldness? (HINT: This requires a dihybrid cross.)

  11. Challenge Problem Solution 50% female (none bald); 25% male (balding); 25% male (not balding) Did the balding sons get their baldness gene from their mother or their father?

  12. References ADAM Inc., Male Pattern Baldness. 14 Apr 2008. U.S. National Library of Medicine 16 Apr 2008 <http://www.nlm.nih.gov/medlineplus/ency/imagepages/17083.htm> ADAM Inc., Various Tests for Color Blindness. 2007. New York Times Company. 16 Apr 2008 <http://www.nytimes.com/imagepages/2007/08/01/health/adam/9962Colorblindnesstests.html>. Biggs, Alton, et. al. Biology. New York: The McGraw Hill Companies, Inc., 2007. Color in Computer Graphics. 25 Feb 1998. Cornell University Program in Computer Graphics. 16 Apr 2008 <www.graphics.cornell.edu/online/tutorial/color/>. Waggoner, Terrace L.. "About Color Blindness (Color Vision Deficiency)." Colors for the Color Blind. U.S. Naval Hospital, Pensacola, FL. 16 Apr 2008 <http://www.toledo-bend.com/colorblind/aboutCB.html>. "X chromosome." Genetics Home Reference: Your Guide to Understanding Genetic Conditions. 14 Apr 2008. U.S. National Library of Medicine. 16 Apr 2008 <http://ghr.nlm.nih.gov/chromosome=X>. “X chromosome.” Photo Researchers, Inc. 16 Apr 2008.

More Related