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 16^th 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

            Disease”)

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

D^A > D^B > D^C > d

D^BD^C vs. D^AD^B = D^AD^C

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

I^A     I^B     i

Blood Type    Genotype

     AB                   I^AI^B

     A                I^AI^A or I^Ai

     B                I^BI^B or I^Bi

     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