chromosomal genetic. linked genes morgan: studied eye color in drosophila (flies) p1 true breeding...
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Chromosomal Genetic
Linked genes
Morgan: studied eye color in Drosophila (flies)P1 true breeding white eyed males mated withP1 true breeding red eye femalesF1: all red eyes (expected)F2: 3:1 red eyes to white (expected)BUT, the white eyes showed up only in MALESAll females had red eyes: about half the males
had red…..the other half of the males had whiteCONCLUSION: 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 DISORDERSRed green color blindness- malfunction in
light sensitive cells in the eyeHemophilia- lack one or more proteins
needed for blood clottingDuchenne muscular dystrophy- progressive
weakening of muscles and loss of coordination
Sex linked recessive
Common Chromosomal Abnormalities
http://anthro.palomar.edu/abnormal/abnormal_4.htm
Two Main Categories Structural modification Irregular number
Typically result from nondisjunction during meiosis
Polyploidy-complete multiples of sets of chromosomes (23+23+23)
Aneulploidy-addition or loss of chromosomes within a set (23+22)
Autosomal Defects
http://anthro.palomar.edu/abnormal/abnormal_4.htm
Down’s SyndromeTypically trisomy of
chromosome 21Some have
translocation of 21 to 14 or 15
2-4% are genetically mosaic
75-80% of Down syndrome children are born to women under 35
MonosomyOnly one set of
chromosomes remains after fertilization
All fetuses will spontaneously abort
Female AbnormalitiesFemale Abnormalities Male AbnormalitiesMale Abnormalities
http://anthro.palomar.edu/abnormal/abnormal_4.htm
Metafemale(XXX) Unusually tall, low to
normal intelligence Normal sex
characteristics, fertileTurner 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