Chromosomal Genetic

Linked genes Morgan: studied eye color in Drosophila (flies) P1 true breeding white eyed males mated with P1 true breeding red eye females F1: all red eyes (expected) F2: 3:1 red eyes to white (expected) BUT, the white eyes showed up only in MALES All females had red eyes: about half the males had red…..the other half of the males had white CONCLUSION: eye color linked to sex of fly

Phenotypes In a cross: the offspring will get either:  Parental phenotype: same as 1 of the parents OR  recombinant phenotype NOT same as either parent

Genetic Recombination Recombination of unlinked genes:  Independent assortment of chromosomes Recombination of Linked genes:  Crossing over

Linkage maps Linkage maps are based on the frequency of recomination. If 50% recombo same as if on separate chromosomes 1% crossing over = 1 map unit

Linkage Map Problems Draw a linkage map(s) for the following recombination frequencies: 1. A-B 30%, B-C 20%, B-D 35%, C-D 25%, A-C 50%, A-D 50% 2. A-C 50%, C-D 15%, A-D 50%, A-B 30%, B-C 50%, B-D 50%

Sex linked recessive traits are more common in MALES

Sex linked disorders (recessive) SEX LINKED DISORDERS Red green color blindness- malfunction in light sensitive cells in the eye Hemophilia- lack one or more proteins needed for blood clotting Duchenne muscular dystrophy- progressive weakening of muscles and loss of coordination

Sex linked recessive

Common Chromosomal Abnormalities 4.htm Two Main Categories  Structural modification  Irregular number Typically result from nondisjunction during meiosis Polyploidy-complete multiples of sets of chromosomes ( ) Aneulploidy-addition or loss of chromosomes within a set (23+22)

Autosomal Defects 4.htm Down’s Syndrome Typically trisomy of chromosome 21 Some have translocation of 21 to 14 or % are genetically mosaic 75-80% of Down syndrome children are born to women under 35 Monosomy Only one set of chromosomes remains after fertilization All fetuses will spontaneously abort

Female Abnormalities Male Abnormalities 4.htm Metafemale(XXX)  Unusually tall, low to normal intelligence  Normal sex characteristics, fertile Turner Syndrome (XO)  Ovaries do not develop, and do not ovulate  Lack secondary sex characteristics  Slight mental retardation Klinefelter Syndrome (XXY)  High-pitched voice  Asexual to feminine body type  Low testosterone, sterile  1 in 500 XYY Syndrome  Unusually tall, severe acne  High testosterone levels, possibly leading to violence Sex Chromosome Abnormalities