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?