6-1 Notes: Chromosomes pg 151-153

fact We have 9 million kilometers of DNA. That’s enough DNA to stretch from the sun and back more than 13 times!! How is all that DNA packed so tightly and squeezed in a nucleus??

DNA condenses into chromosomes using histones

Chromosomes Chromosome: coiled and compact DNA in nucleus Histones: proteins that DNA wraps tightly around

Chromosomes Chromatid: half of a duplicated chromosome went through replication and ready for cell division Chromatids held together by a centromere

Chromosomes Chromosome Number: each organism has a specific number of chromosomes Humans have 46 chromosomes (23 pairs). Chromosome number is not linked to complexity of organism.

Karyotype Photo of chromosomes Stain chromosomes during cell division when DNA is condensed

Karyotype Purpose: Stained bands used to identify chromosomes Identify genetic disorders due to the wrong number of chromosomes Identify sex

Homologous Chromosomes Your body has 23 pairs of chromosomes Each pair referred to as homologous pair Homologous Chromosomes: two chromosomes- one from father and one from mother Both carry instructions for same gene/trait (ex: eye color)

Types of Chromosomes Autosomes: chromosomes #1- 22 Determine most physical traits Homologous

Types of Chromosomes Sex chromosomes: #23 determine sex of the organism (X or Y) female: XX male: XY (not homologous)

Types of Cells Haploid vs. Diploid Use “n” to indicate nuclear state of cell (pairs of chromosomes) Haploid (n): only 1 set of chromosomes (n=23 chromosomes) Diploid (2n): having 2 sets of chromosomes (2n=46 chromosomes) one set from mom and one set from dad

Types of Cells Haploid vs. Diploid 2 haploid cells (sperm and egg) can combine to make a diploid (zygote)

Type of Cells Somatic vs. Gametes Somatic Cells: body cells Make up most of your body tissues and organs. Diploid (2n) Formed by Mitosis

Somatic vs. Gametes Type of Cells Gametes: sex cells Form egg and sperm cells Haploid (1n) Formed by Meiosis