THEODOR BOVERI 1896

AND

WALTER SUTTON 1902

Theodor BoveriPerformed cross-breeding experiments on sea urchins producing hybrids

Noticed some eggs from the female contained no nucleus. He was still able to fertilise them with male sperm and the resultant offspring were not a hybrid but a smaller version of the male parent.

Boveri concluded that is was the something in the nucleus that was responsible for the inheritance of characteristics and not in the cytoplasm.

Walter SuttonFollowed work of Boveri (and other scientists) he concluded that:

# Mendel’s “factors” are located on the chromosomes

# Chromosomes occur as homologous pairs

# As a result of meiosis, each gamete receives only one chromosome of each pair

# The distribution of each member of a homologous pair is independent

Meiosis

Meiosis again - simple

SEGREGATION:Copies of the same gene occur in pairs on homologous chromosomes

1 homologous pair

Gene for widow’s peakMum’s copy Dad’s copy

Only one from each homologous pair ends up in each gamete

Gamete 1Gamete 2

Meiosis occurs

INDEPENDENT ASSORTMENT:

OR

One gene pair will separate independently of other gene pairs on different chromosomes

FOUR DIFFERENT types of gametes

CROSSING OVER:During meiosis homologous chromosome pairs sometimes touch and exchange genes.

Idea not accepted, most scientist believed that each chromosome contained ALL the information for that organism.

Walter Sutton

Theodor BoveriContinued his work with sea urchins and was able to show that each chromosome had different information and each one was needed for the organism to survive.

Sea urchin eggs fertilised with two sperm, when these eggs began to divide the new cells had different combinations of chromosomes