Growth & Development of Organisms-Fertilization and Chromosomes-

Essential Question(copy in the brainwork (left)section of your notebook)

• What are chromosomes?

Fertilization

• Organisms begin as a single cell (fertilized egg) • Zygote

• The fertilized egg gets 50% of its genetic information from mom and 50% from dad

• The cell will divide over and over again to create a complex multicellular organism

Video?

• https://www.youtube.com/watch?v=GZk4hT7ncv0 - skip the first 2 minutes

Before  a  Cell  Divides…•The  DNA  copies  itself  so  it  can  be  placed  in  new  cells.  

• The  DNA  must  become  “travel-­‐ready,”  so  each  strand  coils  and  twists  up  to  form  chromosomes.

It  is  easier  to  transport  these  extension  cords  if  they  are  coiled  up.  Similarly,  it  is  easier  to  transport  DNA  if  it  is  coiled  up.

Chromosome  Formation

Chromosome  Anatomy• Chromosomes: rod-shaped structures

made of tightly coiled DNA and proteins – Each chromosome is a single DNA strand

Sister

Label  the  chromosome!

Each half of a chromosome is called a chromatid (together, they are “sister chromatids”)

Chromosome  Numbers

•Each  species  has  a  certain  number  of  chromosomes  in  each  cell.  –Fruit  Fly  =  8

–Carrot  =  18

–Human  =  46

–Chimpanzee  =  48

–Horses  =  64

Eukaryotes  Have   Sex  Chromosomes  &  Autosomes

•Sex  Chromosomes:  determine  the  sex  of  the  organism.    

•Human  sex  chromosomes:  X,  Y  •Humans  have  one  pair  –XY  (male)  and  XX  (female)

•Autosomes:  term  for  all  chromosomes  EXCEPT  sex  chromosomes.      – Humans  have  22  pairs

•Humans  have  44  autosomes  (22  pairs) +  2  sex  chromosomes  (1  pair)=           =  46  total  (23  pairs)Autosomes

Sex chromosomes

•We  have  two  copies  of  each  chromosome  because  we  get  one  from  mom  and  one  from  dad.    

•Homologous  Pair:  chromosomes  that  are  the  same  size,  same  shape,  and  contain  the  same  genes.

■ Diploid(2n): Cells that have two sets of chromosomes – All cells, except gametes

(sperm and eggs)

■ Haploid(1n): Cells that have only one set of chromosomes – Gametes ONLY

Fertilization – 1n +1n = 2n

Summary1. A  chromosome  is  made  of  tightly  coiled  

__________  and  ____________.  2. Chromosomes  form  because  ____.  3. A  homologous  pair  of  chromosomes  is  ____.  4. Sex  chromosomes  are  different  from  

autosomes  because  ______.  5. The  difference  between  diploid  and  haploid  

cells  is?