Transcript ch 15 chrom Genetics

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?
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
 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)
http://anthro.palomar.edu/abnormal/abnormal_
4.htm
Autosomal Defects




Down’s Syndrome
Typically trisomy of
chromosome 21
Some 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
http://anthro.palomar.edu/abnormal/abnormal_
4.htm
Monosomy
 Only one set of
chromosomes remains
after fertilization
 All fetuses will
spontaneously abort
Sex Chromosome Abnormalities
Female Abnormalities
Male Abnormalities
 Metafemale(XXX)
 Klinefelter Syndrome


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
http://anthro.palomar.edu/abnormal/abnormal_
4.htm
(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