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 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

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