Packaged Instructions for Life

 Chromosomes are packages of DNA wrapped with help of proteins called histones
 Composed of two identical sister chromatids attached at centromere

 Chromosome levels organization:
 dsDNA
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Nucleosome
Coiled solenoid/nucleosome
Chromatin
Supercoiled (condensed) chromatin
Chromosome

 Each sister chromatid contains thousands of identical genes in the same locations on each
 Gene: segment of DNA that codes for specific proteins
 Ex: brown hair, green eyes, etc
Gene A
Gene B
Gene C
Gene D
Gene E

 Each human somatic or body cell contains two copies of each chromosome
 23 sets of chromosomes x 2 = 46 total (other species differ in numbers)
 Combination of all 23 is TOTAL DNA genome (3 billion base pairs)

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rd
 Females have XX
 Males have XY (Y is just shorter)
Females: XX
Males: XY

 Two sets of chromosomes is termed diploid
(somatic cells)
 One set of chromosomes is termed haploid
(gametes)
 Necessary since combination of chromosomes from egg & sperm must be diploid to produce viable (able to live) offspring
 Fertilized egg = zygote haploid diploid

 Diploids have same gene (eye color) but may have different variations (brown vs. blue eyes)
 called homologous chromatids (similar info)
 One from mother, one from father gene for eye color (mom’s brown eyes) dad’s blue eyes

All body cells
2 sets of chromosomes
Only eggs or sperm
1 set of chromosomes
46 chromosomes (1-23 twice) 23 chromosomes (1-23)
Diploid Haploid
Homologous pairs No pairs

 Map of all 23 sets of chromosomes from a body/somatic cell is called a karyotype
 Numbered from 1 – 23 based on length, location of centromere, and banding pattern
 #1-22 are called autosomes, #23 are sex chromosomes

male

 Karyotypes are usually only completed for cases where there might be a chromosomal abnormality
 Monosomy (missing homolog)
 Trisomy (Extra homolog)
 Incorrect sex chromosome numbers

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