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Flashcards in chromosome and cell division mw% + Deck (21)
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1

Name the components of a eukaryotic chromosome structure?

•Telomere

•Centromere

•Heterochromatin

•Euchromatin

2

                  What is the function of a telomere?

  • 5’-TTAGGG-3’ repeats
  • Prevent end-replication problem
  • Protects the end of the chromosome from deterioration or from fusion with neighboring chromosomes.

3

Describe the components of the cell cycle?

  1. Interphase:
  • G0: Exit from cell cycle. Stopped undergoing mitosis indefinitely
  • G1 : Cell growth. Metabolically active; duplicates organelles and cytosolic components and centrosome replication begins
  • S: DNA Replication
  • G2: Preperation for mitosis. Cell growth continues; enzymes and other proteins are synthesized; centrosome replication completed.

   2. Mitotic phase 

 

4

Prophase

  • Chromosomes condense
  • Nuclear membrane disappears
  • Spindle fibres are made from the centriole

 

5

Metaphase

  • Chromosomes aligned at the equator of the cell
  • Fibre attaches to each centriole (on chromosomes Kinetochore )
  • Maximum condensation of chromosome

Note: Long protein fibers called microtubules extend from the centrioles in all possible directions, forming what is called a spindle fibres

6

Anaphase

  • Sister chromatids separate at centromere
  • Separate longitudinally
  • Move to opposite ends of cell

7

Telophase

  • New nuclear membranes form
  • Each cell contains 46 chromosomes (diploid)

8

Cytokineses

  • Cytoplasm separates
  • Two new daughter cells

9

What are centromeres?

Constricted region joining sister chromatids

Repetitive DNA sequences

•Site of kinetochore (where the spindle fibers attach during cell division to pull sister chromatids apart)

•Protein complex that binds to microtubules

•Required for chromosome separation during cell division

10

What are the componets of chromatin?

Heterochromatin

–Condensed structure

–Silenced genes

Euchromatin

–Open structure

–Active genes

11

Chromatin structure

•DNA packaged with histone proteins to form chromatin

•Histones have positive charge

•Packaged into units called nucleosomes

•From ‘solenoid’ structure

 

12

What is the purpose of packaging DNA?

•Negatively charged DNA neutralised by positive charged histone proteins

•DNA takes up less space

•Inactive DNA can be folded into inaccessible locations until required

13

Briefly describe Meiosis

•Cell division in germ cells: spermatogonium and oogonium

•Diploid cells (in ovaries and testes) divide to form haploid cells

•Chromosomes are passed on as re-arranged  (recombined) copies

–Creates genetic diversity

14

Gametogenesis

Oogenesis = process of egg formation

Spermatogenesis = process of sperm formation

•Both go though several stages, with different timing in males and females

•Sperms go through more cell divisions than eggs do – more chance of mutation

15

What is fertilisation?

•Two haploid cells form 1 diploid cell (zygote) – develops into embryo

•Whether sperm contain an X or Y chromosome determines if embryo is female (XX) or male (XY)

•Embryo contains an assortment of genes from each original parent – more genetic diversity

•Mitochondria (and their DNA) come only from mother via the egg – maternal inheritance

16

What does X-inactivation in female mammals prevent?

  • Double dose of gene products
  • As all female mammals have wX chromosomes, X-inactivation prevents them from having 2X as many X chromosome gene products as males, who only possess a single copy of the X chromosome 

17

    Extragenic sequences

Tandemly repeated (nucleotide repeat) DNA sequences

18

Meiosis and recombination pic

19

Karyotype  

  • Karyotype is a test to identify and evaluate the size, shape, and number of chromosomes in a sample of body cells.
  • Extra or missing chromosomes, or abnormal positions of chromosome pieces, can cause problems with a person's growth, development, and body functions.

20

    Fluorescent in situ hybridisation (FISH)

a molecular cytogenetic technique that uses fluorescent probes that bind to only those parts of the chromosome with a high degree of sequence complementarity

21

Types of FISH

(telomere pic)

Unique sequence probes

Centromeric probes

–Useful for determining chromosome number

Telomeric probes

–Useful for detecting subtelomeric rearrangements (Subtelomeres are segments of DNA between telomeric caps and chromatin)

Whole chromosome probes

Cocktail of probes covering different parts of a particular chromosome

–Used with different fluorescent dyes

Spectral karyotype

–Useful for detecting translocations and rearrangements