Chromosomes Do not copy the information in blue text

Pair-Share #1: Why do our cells need to divide? Discuss with your neighbor any reasons you can think of that require our cells to make more of themselves! Be prepared to share out!

We need cell division for… A) GROWTH - We all start life as a single cell and our bodies are the result of cell division B) REPAIR - When we cut ourselves, cells divide to heal the wound C) REPRODUCTION - Cell division produces our sex cells D) REPLACEMENT - Cells don’t live forever & need to be replaced –Your skin replaces itself every 30 days

Before a Cell Divides… The DNA makes a copy of itself so it can be placed in a new cell. 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 Chromosomes are made of DNA and special proteins called histones!

Chromosomes: rod-shaped structures made of tightly coiled DNA and histone proteins –Each chromosome is a single DNA strand Sister Sketch & label the chromosome! Each half of a chromosome is called a chromatid (together, they are “sister chromatids”)

Here is what real sister chromatids look like: Here is a short video clip of DNA coiling into a chromosome (1:31) – tch?v=9kQpYdCnU14 tch?v=9kQpYdCnU14

Pair Share #2: What is the purpose of a chromosome? Discuss this with the person next to you: –Why does our DNA wrap around proteins to form chromosomes? Be prepared to share out!

Each species has a certain number of chromosomes in each cell that is considered “normal.” –Fruit Fly = 8 –Carrot = 18 –Chimpanzee = 48 –Horses = 64 –Human = 46

Eukaryotes:  DNA is within the nucleus  DNA is linear in shape Prokaryotes:  DNA is free-floating in the cytoplasm  DNA is circular in shape

Eukaryotes Have Two Types: Sex Chromosomes & Autosomes Sex Chromosomes: determine the sex of the organism. Human sex chromosomes: X, Y –XY (male) and XX (female) –Humans have 1 pair = 2 total Autosomes: term for all chromosomes EXCEPT sex chromosomes. –Humans have 22 pairs = 44 total

44 autosomes + 2 sex chromosomes = 46 total chromosomes Autosomes Sex chromosomes

Homologous Pair: Chromosomes that are the same size, same shape, and contain the same genes. –We have two copies of each chromosome because we get one from mom and one from dad.

Pair Share #3: What’s the difference? Discuss this with the person next to you: –How are sex chromosomes different from autosomes? Be prepared to share out!

Now, we’re ready to divide! Cell Division Video “What is mitosis?” (13:34) BV9tD-A BV9tD-A