#x-linked

[bpod-bpod]

The X Factor

We have 23 pairs of chromosomes, but our gametes, sperm and eggs, only carry one copy of each. To achieve that, precursors called germ cells undergo a form of cell division known as meiosis: in this artificial ovary, lab-grown female germ cells are shown in purple, with those undergoing meiosis in yellow, and supporting cells in cyan. Meiosis has added complications for females, who possess two copies of the X chromosome. To avoid producing a harmful excess of X-linked proteins, one copy of X is inactivated in every cell, but it needs to be re-activated in germ cells. Researchers tracking the status of X chromosomes in cultured mouse cells found that this cycle of inactivation and re-activation is hugely important for efficient meiosis. This could help explain why producing immature eggs, or oocytes, in the laboratory is so difficult; improvements to the process would ultimately benefit research on female fertility.

Written by Emmanuelle Briolat

Image from work by Jacqueline Severino and colleagues

Centre for Genomic Regulation (CRG), The Barcelona Institute of Science and Technology, Barcelona, Spain

Image originally published with a Creative Commons Attribution-NonCommercial 2.0 Generic (CC BY-NC 2.0)

Research published in The EMBO Journal, May 2022

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Concepts of Genetics- Klug and Cummings

Chromosome and hereditary principles.

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Prevent Fatal Diseases - Genetic Carrier Screening Tests

In the recent days we are often listening among our nearest or dearest about the children requiring blood transfusions. Have you ever thought of why such

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Tortoiseshell Cats

I’m sure a lot of you already know this but it’s new to me as I never really thought to look in to it. Today I found out why you can only get female tortoiseshell (aka calico) cats. For those of you who don’t know, it’s through a process called X-inactivation.

Basically, as female mammals have two X chromosomes (XX) and males only have one (XY), cells in the female body ‘silence’ one X chromosome while the organism is still an embryo, as having two can give rise to a potentially toxic dose of proteins. This inactivated chromosome becomes a ‘Barr body’. This happens in us too. Coat colour in these cats is X-linked, so males are either orange or black depending on whether the X chromosome they inherit codes for orange or black. In female tortoiseshell cats, each cell randomly switches off one of the two X-chromosomes, meaning if the female possesses one X chromosome with the gene for orange, and the other for black, each cell shuts one of the two colours down. This results in some areas of skin producing orange pigment and others black.

This is a really simplified version of what’s going on in these cat’s genomes. In real life other genes contribute to the final coat denoting further spotting, additions of white areas and dulling of colours.

Very rarely a male toirtoiseshell is born. This is usually due to an extra chromosome (XXY) meaning the animal is infertile.

I find this picture sums it up perfectly.

[mynotes4usmle]

X-linked Recessive Diseases List

Alport’s Sd: "hereditary nephritis", type IV collagen deficiency, alternating thickening & thinning of GBM, COL4A5 mutation, hearing loss, ocular abnormalities (lens & cornea), hematuria (gross or micro) since childhood.

Bruton’s Agammaglobulinemia: btk gene defect, no mature B cells or plasma cells, low lymphoid tissue, hepatitis, enterovirus infxs, first 6 months protected by maternal ab (no symptoms)

Becker’s Muscular Dystrophy: altered dystrophin gene, later onset than Duchene's, slow progression, relatively normal life span, less severe, rare cardiac involvement.

Chronic Granulomatose Disease (CGD): NAPDH oxidase deficiency, recurrent catalase (+) infxs, nitroblue tetrazolium test negative (yellow)

Congenital Aqueductus Stenosis: MCC of congenital obstructive hydrocephalus.

Color blindness (red-green): can't distinguish shades of red and green (usually blue-green)

Duchene’s muscular Dystrophy: dystrophin gene mutation (Xp21), absent dystrophyn protein, MC & severe of muscular dystrophies, normal until 5yo, short life span (

Fabry’s Disease: alpha Galactosidase A, Ceramide trihexose accumulation, angiokeratomas, renal failure, peripheral neuropathy.

Glucose 6-P Dehydrogenase (G6PD) Deficiency: chronic hemolytic anemia, MCC of enzymatic deficiency HA, Heinz bodies, bite cells. Triggers are infections, drugs (antimalarial), fava beans

Hemophilia A & B: factor VIII & IX deficiency respectively. PTT prolongation.

Hunter Disease: iduronate sulfatase deficiency, heparan sulfate accumulation, no corneal clouding, aggressive behaviour.

Inherited Nephrogenic Diabetes Insipidus: V2 receptors in collecting duct don't respond to ADH.

Lesch-Nyhan Sd: HGPRT1 deficiency, spastic cerebral palsy, self-mutilation, hyperuricemia, oral crystals in diapers, early death.

Menkes Disease: ATP7A gene mutation (copper efflux protein), Cu+ is lysil oxidase cofactor, Cu+ accumulates in intestine & kidneys; deficient in other tissues = deficient collagen cross linking; steely 'kinky' hair, MR, arterial tortuosity, hypotonia.

Ornithine Transcarbamoylase Deficiency: urea cycle, orotic aciduria + hyperammonemia (no megaloblastic anemia), orotic acid accumulation, increased glutamine . Cerebral edema, lethargy, vomiting, hyperventilation, convulsions, coma, death.

SCID: IL-receptor, Gamma chain deficiency

Wiskott Aldrich Sd: combined partial B & T immunodeficiency, IgM deficiency, thrombocytopenia, eczema.

[fuckyeahmedicalstuff]

X-Linked chondrodysplasia punctata

The irregular bone growth and uneven limbs is characteristic of chondrodysplasia punctata, along with cartilage anomalies such as flattening of the tip of the nose. Fetus had x-linked recessive chondrodysplasia punctata and survived to 16 weeks. Not an automatically fatal genetic mutation, but causes growth, dermatological, osteological, and developmental problems.