Lecture 3 - Somatic polyploidy

Counting Chromosomes

• what do c + n represent?

c = amount of DNA in a gamete (# of base pairs)

n = # of chromosomes in a gamete

What is an exception to diploidy in cells in normal adults?

Sex chromosomes

• XY

What are 2 organisms mentioned in class that are Diploid

Humans: 2n = 36

Drosophila: 2n = 8

Define Euploid vs. aneuploid

Euploid = Normal # of chromosomes

Aneuploid = Abnormal # of chromosomes

What does Polyploidy mean?

Adults have more than 2 of each chromosome

• triploid, tetraploid, hexaploid + octoploid

What are 2 examples of polyploidy covered in class?

• Banana = triploid

• Durum (pasta wheat) = Tetraploid

  • both are germline polyploids

****Define Germline polyploid

ALL cells (both gametes + somatic) have extra chromosomes

******Define somatic polyploidy

SOME cells are polyploid in an otherwise DIPLOID organism

What are 2 pros + 1 con of polyploid cells?

Pros:

1. Larger

2. Export more proteins

Cons:

• Can’t reproduce (in most cases)

********What are 4 possible mechanisms that result in Somatic polyploidy?

1. Cell fusion

2. Skip cytokinesis

3. Skip Telophase + cytokinesis

4. Skip mitosis + cytokinesis

Mechanism #1: Cell fusion

• diagram of process

• Example given in class

• Type of cell that results

Type of cell resulting = MULTINUCLEATED

eg. Human skeletal muscle cells

Mechanism #2: Skip cytokinesis

• diagram of process

• Example given in class

• Type of cell that results

Type of cell resulting = MULTINUCLEATED

eg. Drosophila Embryos

• use somatic polyploidy to speed up embryogenesis (egg needs to become larvae ASAP = larvae temp. somatic polyploid)

Mechanism #3: Skip telophase + cytokinesis

• diagram of process

• Examples given in class

• Type of cell that results

Type of cell resulting = MONO-nucleated

eg. Human MEGAKARYOCYTE WBC

• use somatic polyploidy to get large “Giant nucleus cell”

• Purpose = PLATELETS

RBC + Nucleus?

Expel the nucleus during maturation = NO NUCLEUS

why?

• Without nucleus = smaller + more flexible = can get through capillaries

Mechanism #4: Skip Mitosis + cytokinesis

• diagram of process

• Examples given in class

• Type of cell that results

Type of cell resulting = MONO-nucleated

eg. Drosophila larvae ORGANS

• Larvae have both larval organs: don’t need to reproduce = POLYPLOID

• And future adult organs (imaginal discs): Must reprod = DIPLOID

The example of Drosophila larvae somatic polyploidy covered in class

• Infodump

• What cell

• Function/purpose

Salivary gland = Massive (1 giant nucleus)

• Why so large?

  • To make more proteins (Salivary glue proteins) made by Sgs gene

• salivary glue proteins = cover entire larvae to make it sticky + stick to surfaces to pupate

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