Lecture # 20
Chromosomal sex
karyotying
Chromatin bodies
Barr bodies
Normal human females (XX) have one chromatin body.
Normal human males (XY) have no chromatin body.
A chromatin body is an inactive X-chromosome.
Females with Turner’s Syndrome (X) have no
chromatin body.
Individuals with 3 X-chromosomes have 2
chromatin bodies.
Individuals with Klinefelter’s Syndrome
(XXY) have one chromatin body.
Inactivation of all but one X-chromosome in
a cell.
Amniotic fluid
Chromatin bodies appear in human embryos only
after the 16th day of development.
X-chromosomes are inactivated randomly.
Mosaic patterns in adult organisms
Calico cats
Tortoise shell coat pattern in mice
Sex-linked traits
AY if on the X-chromosome
XB if on the Y-chromosome
Sex-linked traits on the X-chromosome in males
are inherited from the mother’s side of the
family.
Heterozygous females are carriers of the recessive
expression.
The father determines the sex of a child.
Sex-linked traits were discovered with
white-eyed fruit flies.
Sex-linked traits in humans on the
X-chromosome:
Hemophilia (“bleeder’s d isease”)
Colorblindness
Sex-linked traits in humans on the
Y-chromosome:
Hairy earlobes
Sex-influenced traits are inherited by genes on
the autosomes but the expression of the trait
is influenced by the sex of the individual.
Hormones are the basis for the expression of
most sex-influenced traits.
4. Multiple Alleles
Allelomorphic expressions
Allelomorphs
Allele
If there are more than two alleles for a locus,
the condition is called multiple alleles.
Superscripts
DA > DB > DC > d
DBDC vs. DADB =
DADC
Human hairdresser genes:
kinky>curly>wavy>straight
Coat color in rabbits:
wildtype>chinchilla>Himalayan>albino
Immunology
Antibody
An antigen is an ANTIbody GENerator.
Blood Type Antigens
AB both A and B
A A
B B
O neither A nor B
IA IB i
Blood Type Genotype
AB IAIB
A IAIA or IAi
B IBIB or IBi
O ii
Blood typing can be good negative evidence.
1900 Landsteiner
Blood
Type
Antigens
Antibodies
AB both
A and B neither a nor b
A
A
b
B
B
a
O
neither A nor B both a and b
The reaction that occurs between the donor’s
antigens and the recipient’s antibodies
Type AB blood is the universal recipient.
Type O blood is the universal donor.
Rejection
Rh system
Rh rh
Rhesus monkeys
Rh-positive: RhRh or Rhrh
Rh-negative: rhrh
In the second and subsequent children born
to an Rh-positive man and an Rh-negative woman.
Erythroblastosis fetalis
Rhogam
Inbreeding is the mating of closely related
individuals.
Outbreeding is the mating of unrelated
individuals.
Heterosis or Hybrid Vigor