FEBRUARY 20, 2015
Journal: Where is DNA found inside a cell?
CHROMOSOMES AND KARYOTYPES
CHROMOSOMES
Usually DNA inside the nucleus is wrapped around proteins to form an ‘X’ shape
These ‘X’ shaped coils of DNA are called chromosomes
CRITICAL THINKING QUESTION
Why is DNA coiled up and not just a big clump in the nucleus?
CHROMOSOME STRUCTURE P arm: Short arm of the chromosome Q arm: Long arm of the chromosome Centromere: midpoint where the two
sides of the ‘X’ cross
SISTER CHROMATIDS
Two identical halves of a single replicated chromosome
Contain the same DNA on each half
NUMBER OF CHROMOSOMES
The same for each cell in the body, except sex cells which only have half a set of chromosomes.
Each individual has the same number of chromosomes their entire life
The number of chromosomes is the same across an entire species.
Organism Chromosome numbers
Human 46
Chimpanzee 48
House Mouse 40
Corn 20
HUMAN CHROMOSOMES
TYPES OF CHROMOSOMES
Autosomes 22 pairs Contain all other traits
Sex Chromosomes One pair Determines your gender
IDENTIFYING CHROMOSOMES
Chromosomes can
be identified by their: Size Shape Gene Banding
Pattern
KARYOTYPE An organized arrangement of a
person’s chromosomes. Allows you to determine gender and
chromosomal abnormalities.
DETERMINING GENDER USING A KARYOTYPE
Female: XX Male: XY
DETERMINING CHROMOSOMAL ABNORMALITIES USING A KARYOTYPE
If the number of chromosomes in a karyotype does not equal 46, then a chromosomal abnormality has occurred.
Differences in chromosome number causes disease.
CHROMOSOMAL ABNORMALITIES
Trisomy 21 also known as Down’s Syndrome
Extra chromosome #21
CHROMOSOMAL ABNORMALITIES
Trisomy 18 also known as Edward’s Syndrome
Extra chromosome #18 Results in heart and mental defects and
overlapping fingers
CHROMOSOMAL ABNORMALITIES
Turner’s Syndrome: XO Females with underdeveloped ovaries Typically have short stature
CHROMOSOMAL ABNORMALITIES
Klinefelter’s Syndrome – XXY Males with little body hair present. Typically tall. Some development of breast tissue
normally seen in females.