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.