for adding nucleotides has to move backwards away
from the replication fork; synthesis is therefore not
continuous, but in repeated steps.
There is a gap between the final lagging strand seg-
ment and the end of the chromosome. As a result, the
5’ end of the lagging strand will lose some nucleotide
every time a cell replicates its DNA.
See alsoLEADING STRAND.
Lamarckism The idea, promoted by Jean Baptiste de
Lamarck, that acquired traits can be passed from par-
ent to offspring, i.e., that characteristics or traits
acquired during a single lifetime can be transmitted
directly to offspring.
land bridges Pieces of land once connecting the con-
tinents that have since sunk into the sea as part of a
general cooling and contraction of the Earth. Believed
to have served as migratory passages for animals,
plants, and humans.
Landsteiner, Karl(1868–1943) Austrian Biochemist
Karl Landsteiner was born in Vienna on June 14, 1868,
to Leopold Landsteiner, ajournalist and newspaper
publisher, and Fanny Hess. Landsteiner studied
medicine at the University of Vienna, graduating in
1891.
From 1898 until 1908 he held the post of assistant
in the university department of pathological anatomy
in Vienna. In 1908 he received the appointment as pro-
sector in the Wilhelminaspital in Vienna, and in 1911
he became professor of pathological anatomy at the
University of Vienna.
Landsteiner, with a number of collaborators, pub-
lished many papers on his findings in anatomy and
immunology, such as the immunology of syphilis and
the Wassermann reaction, and he discovered the
immunological factors, which he named haptens. He
also laid the foundations of the cause and immunology
of poliomyelitis.
His 1901 discovery of the major blood groups
and his development of the ABO system of blood typ-
ing and 1909 classification of the blood of human
beings into the now well-known A, B, AB, and O
groups, as well as the M and N groups, made blood
transfusion a routine medical practice. For this work,
he received the Nobel Prize for physiology or
medicine in 1930. In 1936 he wrote The Specificity of
Serological Reactions,a classic text that helped to
establish the science of immunochemistry. In 1940 he
discovered the Rh factor, the protein on the surface of
red blood cells that determines if the blood type is
positive (Rh-positive) or negative (Rh-negative). If the
mother has a negative Rh factor (Rh-negative) and the
father and fetus are Rh-positive, the mother can
become Rh-sensitized and produce antibodies to com-
bat fetal blood cells that cross the placenta into her
bloodstream. These antibodies can destroy the fetus’s
Rh-positive blood cells, putting it at serious risk of
anemia.
In 1939 he became emeritus professor at the Rock-
efeller Institute. On June 24, 1943, he had a heart
attack in his laboratory and died two days later.larva The solitary live, but sexually immature,
form of a variety of animal life cycles, e.g., butter-
flies, flies, wasps, that may, after reaching adulthood,
be completely different in morphology, habitat
requirements, and food needs. Some larvae have
other names, like maggots for flies, grub for beetle
larvae, tadpoles for frogs, etc. Insect larvae may molt,
i.e., shed layers of skin, several times during their
development.latentiated drug SeeDRUG LATENTIATION.lateral line system A sensory system composed of a
longitudinal row of porelike openings that open into
tubes in skin on the sides of fish and larval amphibians
that is used to detect water and electrical disturbance in
their surroundings. The ampullary organs, or ampullae
of Lorenzina in fish, detect weak electrical currents
generated by other animals, while the neuromasts—a
small group of pairs of oppositely oriented hair sensory
cells embedded in a gel-filled cupula on either side of
the skin surface or in pit organs—detect the direction
of water movement. The lateral canal is the portion
of the system located on the head, beginning at the196 Lamarckism