Genetics Inheritance The Chromosome Theory of Inheritance Chromosome

Genetics & Inheritance The Chromosome Theory of Inheritance

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

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

Gene Linkage

Barbara Mc. Clintock & Harriet Creighton (1950): Studied Zea mays ; corn b ØLooked at chromosome #9 ØThey noticed that 2 copies of it were different sizes ØConclusion = 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!

Human Chromosomes

Which Parent determines the sex of the child?

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 b b

MODES OF INHERITANCE

MODES OF INHERITANCE b · b b b 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) b RR x WW RW x RW

MODES OF INHERITANCE

MODES OF INHERITANCE b 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.

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

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

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

Rh Factor b Rh Factor = (Rhesus monkey) You either have it (+) or you don’t (-) b Sensitization can occur by: –. )Rh+ blood transfused into Rh- person –. )Rh- mother carries a fetus who is Rh+ b I AI A x I BI B I AI ix I BI i

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

MODES OF INHERITANCE b 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.

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

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

MODES OF INHERITANCE • 12. Dihybrid Crosses: follow 2 traits at a time (Aa. Bb) b Example: A = purple flowers, a = white B = Tall, b = short b 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.

Dihybrid Crosses b. F = first b O = outside b I = inside b L = last = 100% Aa. Bb b AABB x aabb Results --> b Rr. Yy x Rr. Yy

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

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

Genetic Disorders b 2. Chromosome Abnormalities: not caused by a gene b 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. b Ex. Down Syndrome “Trisomy 21”

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

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

THE END!!