Genetics & Inheritance

1. Genetics & Inheritance The Chromosome Theory of Inheritance

2. Chromosome Theory of Inheritance: • Genes that code for various traits are found on chromosomes which are made of DNA and found in the nucleus of each cell

6. Thomas Hunt Morgan (1910): Studies Drosophiliamelanogaster ;common fruit fly • Discovered the gene for eye color and wing size were both located on the same chromosome (X) = Linkage • Linkage = genes located on the same chromosome • The closer the genes are on the chromosome, the greater the likelihood of crossing over • The Law of Independent Assortment does not apply to linked genes!

7. Gene Linkage

8. Barbara McClintock & Harriet Creighton (1950): Studied Zea mays ; corn • Looked at chromosome #9 • They noticed that 2 copies of it were different sizes • Conclusion = Crossing Over had occurred, an abnormal event caused a piece of another chromosome to attach itself to one of the copies of chromosome #9 • Crossing Over disrupts normal Linkage Groups!

9. Human Chromosomes

11. Which Parent determines the sex of the child?

12. MODES OF INHERITANCE • Different ways of inheriting genetic traits • 1. Complete Dominance: dominant allele completely masks out the recessive trait (AA, Aa) • Autosomal Dominant = trait carried on an autosome by a dominant gene (A) • Autosomal recessive = trait carried by a recessive allele (aa) • Example: flower color in pea plants • P = Purple, p = white

13. MODES OF INHERITANCE

14. MODES OF INHERITANCE • 3. Codominance: both alleles express themselves when heterozygous (Blood types A, AB, B, O). There is no true recessive trait. • AB Blood type is an example of Codominance = Both alleles in the heterozygous form (IAIB ) end up expressing themselves equally. Both traits show up in the phenotype. • Example: coat color in horses • RR = red , WW = White , RW = roan • (RR = red , R’R’ = White , R R’ = roan) • RR x WW RW x RW

16. MODES OF INHERITANCE

17. MODES OF INHERITANCE • 6. Epistasis = one gene affects the phenotypic expression of a second gene. (Skin pigmentation) One gene codes for color, the other codes for the amount of pigment.

18. MODES OF INHERITANCE • 7. Multiple Alleles: a gene having more than two alleles (Blood types) • PHENOTYPES% of PopulationGENOTYPES • A 39% IAIA , IAIi • B 12%IBIB , IBIi • * AB 4% IAIB • O 45% IiIi

20. Blood Types • Discovered in 1900 by Dr. Karl Landsteiner • Based on the presence or absence of specific agglutinogens (clotting factors) on the surface of red blood cells (RBC’s = Erythrocytes) • For example: a person with blood type A posseses A-antigens and Anti-B antibodies • The blood will clot if a foreign Antigen is present

21. Donor vs. Recipient • Universal Donor = Blood type O ; contains no A or B antigens  No Clotting reaction • Universal Recipient = Blood type AB ; contains both A & B antigens  Will recognize antigens from any blood type

22. Rh Factor • Rh Factor = (Rhesus monkey) You either have it (+) or you don’t (-) • Sensitization can occur by: • .)Rh+ blood transfused into Rh- person • .)Rh- mother carries a fetus who is Rh+ • IAIA x IBIB IAIix IBIi

23. MODES OF INHERITANCE • 8. Sex-Linked Inheritance: trait carried on the sex chromosomes; usually the X (XX = female; XY = male) • X-Linked Recessive = Xa (Colorblindness, Hemophilia) • X-Linked Dominant = XA; Y-Linked (Rare) • Carrier = person not affected by the trait but can pass it on to offspring = XA Xa Only females can be carriers for sex-linked traits because if a male has the gene, he will also exhibit the trait!

25. MODES OF INHERITANCE • 9. X – inactivation: one of the two X chromosomes in a female does not uncoil during embryonic development. The chromosome that remains coiled is called a Barr Body and contains genes that will not get expressed. This could cause a sex-linked trait to affect a female that would normally be only a carrier.

27. MODES OF INHERITANCE • 10. Sex-Influenced Traits: expressed in both sexes, but they are expressed differently (Pattern Baldness) • B= Normal; b= Bald • female (bb) = bald; male (bb or Bb) =bald • BB x Bb Bb x Bb

29. MODES OF INHERITANCE • 11. Sex-Limited Traits: autosomal traits expressed in only one sex (Lion’s mane)

30. MODES OF INHERITANCE • 12. Dihybrid Crosses: follow 2 traits at a time (AaBb) • Example: A = purple flowers, a = white B = Tall, b = short • If you cross two parents, where the father is AABB and the mother is aabb: the possible gametes are AB x ab. This can be determined using the F.O.I.L method.

31. Dihybrid Crosses • F = first • O = outside • I = inside • L = last • AABB x aabb --> • RrYy x RrYy Results = 100% AaBb

33. GENETIC DISORDERS • Disorders or diseases related to a persons genes or chromosomes; inherited in the same ways as other traits. • 2 Mechanisms exist:

34. Genetic Disorders • 1. Inherited on Genes: inherited as a trait (Autosomal, sex-linked, sex influenced, etc...) • colorblindness • hemophilia “bleeder’s disease” • muscular dystrophy • albinism • Progeria

36. Genetic Disorders • 2. Chromosome Abnormalities: not caused by a gene • A.) Extra or Missing Chromosomes. Aneuploidy = abnormal chromosome number • Non-Disjunction = failure of chromosome pairs to separate properly during meiosis, end up with daughter cells having either too many or not enough chromosomes in them. • Ex. Down Syndrome “Trisomy 21”

39. Genetic Disorders • B.) Mutated Chromosome = damaged DNA, genes located in that section are damaged • Deletion: missing gene or piece of chromosome • Duplication: extra piece, genes duplicated • Translocation: gene switches chromosomes • Inversion: fragment of gene gets turned around

41. SCREENING FOR DISORDERS • 1. Karyotyping = genetic map of all the chromosomes that an organism possesses • 2. Amniocentesis = test done before birth, take sample of amniotic fluid (C.V.S.) • 3. Genetic Counseling = determine family medical history

45. THE END!!