Chromosomal Genetic

Why are some traits inherited in ways other than Mendel’s? Linked genes Gene (chromosome) mapping

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

When homologous chromosomes pair and crossing over occurs, new gene linkages can result. Genes that are far apart on the same chromosome should be separated more often than genes that are close together. Morgan was able to calculate mathematically how close or far apart each particular gene pair seemed to be based on the frequency of crossing over. map?

Example: Genes A, B, C, and D are on the same chromosome. The following represent the frequency with which these genes are separated during crossing over : A – B 8% A- C 28% A- D 25% B- C 20% B-D 33% What is the order of these genes on a chromosome

D – A – B - C

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