12th lesson CSI- Identity 2- Karyotype

Today, we learnt more about chromosomes and most importantly about karyotyping.

We started the lesson with a revision on DNA and chromosomes.

What is DNA?

DNA is the instructions for the cell's function, which is located in the nucleus.

DNA encodes detailed set of plans. JUST LIKE BLUEPRINTS :)

DNA- Sugar phosphate backbone
- The four bases: A, T, C, G
- Hydrogen bonds that bond the bases together as much as possible to form 3 dimensional helix bridge

DNA strand made of letters-> letters make words-> words make "sentences" -> genes, which tell cells to make other molecules such as proteins.

What is gene? 

Genes: instruction manuals for our bodies, directions for building all the proteins that make our bodies function.

For eg: Haemoglobin gene
- If it's normal, then the protein works fine

The difference! 

- But if the gene is "mutated", changes in haemoglobin protein such as "sickle cell anemia"

For eg: Enzymes that produce pigment in our eyes and keratin that make our hair/ nails grow.

What is chromosome?

structure of chromosome :)

- It is the storage for DNA
Firstly, the double helix of DNA is formed.
Then the DNA is wrapped around proteins.
Lastly the proteins are packed to form chromosomes.

Most of us get 46 chromosomes. XX-> girl XY-> boy

Not all organisms have the same no. of chromosomes. For eg: humans= 46, onions= 16, mosquitoes=6, carp=104

HOW TO IDENTIFY CHROMOSOMES? 

- SIZE
- BANDING PATTERN (location of giemsa bands on chromosomes make each chromosome pair unique)
- CENTROMERE (position of it)

Karyotype-

a karyotype :)

An organised profile of a person's chromosomes. They are arranged and numbered by size, from largest to smallest. This helps to quickly identify the chromosomal alterations that may result in a genetic disorder.

How to do this?
Scientists take picture of someone's chromosomes, cut them out and match them up using size, banding pattern and centrometre position as guides.

We did this based on two sheets of chromosomes given to us and we cut out each chromosome. Then, we arranged them in order and tried to find out the chromosomal alterations to find out which syndrome the person has and if he/ she actually has a syndrome.

This is the process of how the karyotype is prepared:

the process ! gah it's blurred :(

1.) Blood culture is centrifuged to separate the blood cells from the culture fluid
2.) The fluid is discarded and a hypotonic solution is mixed with the cells. This makes the red blood cells swell and burst. The white blood cells swell but do not burst and their chromosomes spread out.
3.) Another centrifugation step separates the swollen white blood cells. The fluid containing the remnants of the rbc is poured off. A fixative is mixed with the white blood cells. A drop of the cell suspension is spread on a microscope slide, dried and stained.
4.) The slide is viewed with a microscope and images of the metaphase chromosomes are sorted by size and shape on a computer.
5.) The resulting display is the karyotype.

I have researched on some syndromes caused by chromosomal alterations:

1.) Trisomy 13- Patau Syndrome
- Not inherited
- Presence of 3 chromosome 13s in all cells
- Occurs 1 in 10000

*Trisomy 13 mosaicism- presence of an extra chromosome 13 in SOME cells
*Partial Trisomy 13- presence of an extra chromosome 13 in the cells

Symptoms:

Cleft Lip

Clenched hands

- Close set eyes

- Decreased muscle tone

- Extra finger/ toes 

- Hernias (bulge in an organ) 

- Hole, split, cleft in iris (coloboma) (Blurred vision, ghost image, can't see things clearly)

- Low-set ears 

- Scalp defects 

- Seizure

- Single palmar crease (indicate problems with development)

- Skeletal abnormalities

- Small eyes

- Small head 

- Small lower jaw

- Undescended testicle

MEDICAL PROBLEMS: congenital heart disease-> abnormal placement of heart to right side instead of left

2.) Trisomy 18- Edwards Syndrome 

- Extra chromosome 18 

- Occur in 1 in 3000 live births

- Most Edwards Syndrome babies die before birth

Symptoms: 

- Nervous system and brain-> mental retardation, delayed development, high muscle tone (rigid in the limbs, delayed gross and fine motor skill development, stiff legs have difficulty relaxing muslces), seizures, physical malformations (brain defects)

-Head and face-> small head, small eyes, wide-set eyes, small lower jaw, heart: congenital heart defects, bones: severe growth retardation, clenched hands with 2nd/ 5th fingers on top of others, hands and feet defects, malformations of digestive tract, urinary tract and genitals. 

3.) Trisomy 21- Down Syndrome 

- Extra chromosome 21

Physical defects: flat face profile, upward slant to eyes, small ears and protruding tongue 

'

Hypotonia- "floppy"-> tend to reach developmental milestones: "sitting up", "crawling", etc. slowly. 

Digestive issues, problems with feeding, dressing and toilet teaching. 

Medical problems:

- Increased risk of pulmonary hypertension: irreversible damage to lungs

- Problems with hearing + vision (cataracts, structural problems, fluid buildup in inner ear, cross eyed, near sightedness or farsightedness 

- Thyroid problems

- Intestinal abnormalities

- Seizures

- Respiratory problems

- Obesity

- Higher vulnerability to infection

- Higher risk of childhood leukemia  

This is a video intro to karyotype:)