Telomeres- Protective caps on chromosomes

• consists of DNA associated with proteins in chromatins

• might be involved in both aging and cancer

• the same sequences of bases repeated over & over

• Telomere sequence in humans: TTAGGG

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Function of telomere

• help organize 46 chromosome in the nucleus

• DNA is left undamaged in the chromosome during DNA replication

• Important DNA would be lost everytime a cell divides without a telomere

  • Leads to the loss of entire genes

Karyotypes and Nondisjunction

Karyotypes: individual’s complete set of choromosomes

Nondisjunction: cell division during which sister chromatids fail to separate properly

• occurs in any organism in which gametes are produced through meiosis

• associated with serious human disorders

Outcomes of nondisjunction:

• it leads to daughter cells with abnormal numbers of chromosomes, known as aneuploidy

Two types of nondisjunction:

• Mitotic nondisjunction

  • occurs in anaphase when sister chromatids fail to separate

• Meiotic nondisjunction

  • homologous chromosomes fail to segregate at anaphase I and lead to haploid cells with abnormal number of chromosomes(meiosis I)

  • sister chromatids fail to separate and leads to half of the haploid cells with abnormal chromosomes(meiosis II)

  • loss or gain of one or more chromosomes

• Having a set of three chromosmes of one kind - Trisomy (2n+1)

• Having only one of particular type of chromosome - Monosomy(2n-1)

• The loss of both pairs of homologous chromsomes Nullisomy (2n-2)

• Chromosomes are inherited from one parent only Disomy (n+1)

Cause of Nondisjunction

Cellular Differentiation and Stem Cells

Cellular differentiation

• all cells in the body strts at fertilized egg with unique genetic expression

• It needs to manipulate genes that will be expressed and developed

  • This is done through transcription factors: one of a class of proteins that bind to specific genes on the DNA molecule promoting or inhibiting transcription.

Stem Cells

• type of cell that can be directed to become a specialized cell.

• can divide without limit as needed under specific conditions

Two types of stem cells

1. Embryonic stem cells

2. Adult stem cells