The Chromosome

Keypoint # 1: Each chromosome is a tightly coiled string of DNA Each chromosome is made out of ONE long piece of DNA packed into a tight shape Why coiled? Because each DNA strand can stretch out to 5 FEET LONG when unwinded. Chromosomes are the unit of heredity, they need to be passed from one generation to the next

Chromosomes are found in two shapes A chromosome can be two columns of DNA joined in the middle by a centromere to look like a big X (normal) When it looks like a big X, the left and right are identical to each other (same genes) A chromosome can be one column of DNA (after meiosis- we will get to this!) same gene Each of these are considered ONE chromosome

Keypoint #2: Genes are the sections of chromosomes that code for traits Each chromosome has its own set of GENES Genes = sections of DNA that code for traits Traits = expressions of your genes in the body (like eye color, blood type, ear lobe size, etc) brown hair gene Type A blood gene

egg cell and sperm Cells Keypoint #3: There are two categories of cells in the body: Somatic and Sex Cells Somatic cells = BODY CELLS. All of the cells in your body other than sex cells. Sex Cells (gametes) = sperm in males; egg cells in females muscle cells lung tissue cells brain cells egg cell and sperm Cells

Keypoint # 4: Somatic cells are Diploid and sex cells are Haploid Diploid(2n)= 2 of each chromosome. All somatic cells are diploid. D = double the # of chromosomes Haploid (n) = 1 of each chromosome. All sex cells (gametes) are haploid H = half the # of chromosomes

Chromosome Numbers Review One set of chromosomes is represented by the letter n Haploid Cells (gametes) = n chromosomes Diploid Cells (somatic cells) = 2n chromosomes

In humans: There are 23 pairs of Chromosomes in every somatic cell Every person gets a set of 23 chromosomes from each parent 23 from mom + 23 from dad = 46 total (DIPLOID)! images showing all 23 pairs (46) are called Karyotypes

In humans: There is one set of 23 chromosomes in every sex cell There are 23 chromosomes in a sperm cell (male gamete) There are 23 chromosomes in an egg cell (female gamete) Only 23 chromosomes in a cell = HAPLOID

Every pair of chromosomes is unique Each pair of chromosomes has their own set of genes that are always on that # chromosome ex: Chromosome #19 always has the gene for hair color (you have two #19- one from mom and one from dad) The Special #23 pair: XX or XY X and Y = Sex chromosomes Y + X = male X + X = female male or female?

Guided Practice Each chromosome is made of ____(#) strand of ________ Chromosomes have sections called ________ that code for ________ which are expressions of genes

# of chromosomes in humans Somatic Cells Sex Cells (gametes) What kind of cells? # of chromosomes in humans Haploid (n) or Diploid (2n)