Cytogenetic Methods and Trisomy Syndromes

Cytogenetic Methods

• Cytogenetic is the study of chromosomes during cell division
• Karyotyping and G-banded are techniques used in cytogenetics
• Karyotyping is an overall view of all chromosomes, used to identify abnormalities and sex
• G-banding produces visible karyotypes by staining chromosomes with Giemsa
• The human karyotype consists of 23 pairs of chromosomes: 22 autosomes and 1 sex pair (XX for female, XY for male)
• Trisomy occurs when there are 3 chromosomes in one set, resulting in a genetic syndrome

Trisomy Syndromes

• Patau Syndrome (Trisomy 13) causes severe physical and mental abnormalities such as cleft lip, brain defects, and polydactyly
• Edwards Syndrome (Trisomy 18) results in small size, small head and jaw, heart defects, clenched fists, and severe intellectual disability; most babies die shortly after birth
• Down Syndrome (Trisomy 21) causes developmental delays, mild to moderate intellectual disability, and distinctive physical features; people can live healthy and fulfilling lives with support
• Cytogenetics practice examines chromosomes to identify structural abnormalities
• This is performed on dividing cells from tissues like white blood cells, bone marrow, and amniotic fluid
• Staining methods involve cell collection, cell culture for several days, fixation, chromosome spreading on a slide, and stain application for analysis
• Cytogenetics can precisely label chromosome locations using colored dots and be applied to examine any tissue (including tumors) and identify cells with lost or gained chromosomes, translocations, or gene copy number changes
• Cytogenetics helps detect genetic changes in cancer neoplastic cells, especially in hematological malignancies

Biomedical Method and DNA Diagnosis

• Diagnostic tests are used when an individual shows signs or symptoms of a specific condition to provide a definitive diagnosis, better prognosis, medical management, and treatment options
• Genetic testing identifies changes in DNA sequences or chromosome structure, and measures results of genetic changes (RNA analysis or protein output)
• Genetic testing can diagnose suspected genetic disorders, predict risks for specific conditions, customize medical treatments based on genetic makeup, and determine biological relatives (e.g., paternity testing)
• Polymerase Chain Reaction (PCR) amplifies DNA for detection and analysis
• Cell-free fetal DNA (cff DNA) tests are non-invasive, early pregnancy tests on maternal blood for fetal information, highly specific for Down Syndrome
• Newborn Screening identifies genetic disorders in newborns treatable early in life via a blood sample taken 24-48 hours after birth
• Prenatal Diagnosis detects changes in a fetus' genes or chromosomes before birth, offered to couples with increased risk of genetic or chromosomal disorders

Genetic Diseases

• Sickle Cell Anemia is caused by abnormal red blood cells that mishap and turn into crescent discs, cells become sticky and block blood vessels
• Tay-Sachs disease is a Hexa gene mutation that leads to beta-hexosaminidase A deficiency, leading to neurological damage, a cherry red spot in the macula, macrocephaly, hypotonia, motor and mental delay, and convulsions
• Duchenne MD is most common in boys (1 in 3,500)
• Becker MD is milder than Duchenne's, and affects 1 in 30,000 boys
• Limb-Girdle MD appears in teens and young adults in both males and females
• Facioscapulohumeral MD affects the face, shoulder blades, and upper arms in both genders
• Congenital MD is present at birth and affects both males and females

Reproductive Risks

• The risk of having a child with the same diagnosis can be explored after a diagnosis
• Many disorders require both parents to pass on their genes, known as Autosomal Recessive Inheritance, examples are cystic fibrosis
• Cystic Fibrosis (CF) is a genetic condition causing damage to the lungs, digestive system, and other organs; the condition affects cells that produce mucus, sweat, and digestive juices
• CF secretion is thick and sticky, leading to blockages and damage, while normal secretion is thin and slippery

Symptoms and Diagnosis of CF

• Symptoms of CF include persistent cough with thick mucus, recurrent lung infections, wheezing and shortness of breath, poor growth and weight gain, intestinal blockage, a stuffy nose and recurrent sinusitis, greasy and foul-smelling stools, salty-tasting skin, infertility in man, dehydration, and diarrhea
• CF can be diagnosed using screening tests before diagnostic testing to detect early evidence of the disease via maternal blood screening or ultrasound
• Genetic counseling is recommended if screening tests reveal a risk of a health issue or genetic condition

Homeostasis

• Homeostasis is the process of maintaining a constant internal environment, ensuring the body's cells work at their optimum levels
• The body has an automatic control system maintaining constant temperature, steady levels of water, ions, and blood sugar, using a lot of energy even during sleep
• Homeostasis involves organs like the brain, lungs, muscles, pancreas, skin, and kidneys
• Thermoregulation controls the body temperature that varies widely (37°C optimum temperature)
• High temperatures can denature enzymes, while low temperatures slow reactions and can cause cells to die
• Heat can be gained through movement and exercise, shivering and vasoconstriction, and can be lost through sweating and vasodilation

Temperature Control Mechanisms

• Monitoring is performed by temperature receptors in the skin and brain
• The Hypothalamus is the thermoregulatory center in the brain, sending electrical signals to trigger actions that increase or decrease heat loss
• Shivering is an involuntary muscle contraction that generates heat
• Goosebumps occur when tiny muscles at the base of the body hairs pull hairs erect, trapping insulating air
• Vasoconstriction narrows blood vessels in the skin, reducing heat loss and making skin look pale
• Vasodilation widens blood vessels in the skin, increasing heat loss and making the skin look red
• Negative feedback increases imbalance from mechanical condition to further imbalance (e.g., incubators)
• Positive feedback increases imbalance from normal condition, loafing to further imbalance (e.g., childbirth)

Osmoregulation and Glucose Regulation

• Osmoregulation controls water and ion balance; water can be gained during respiration/absorption and lost through exhaled air, sweat, urine, and feces
• Dehydration occurs when the body loses too much water through heavy sweating, low water intake, caffeine, and diarrhea, causing dizziness, dry mouth, concentrated urine, and can lead to death
• Glucoregulation is the regulation of blood glucose levels; blood sugar increases with eating and decreases with exercise
• The pancreas monitors and controls blood glucose
• Insulin is released when blood glucose is high, storing excess glucose and glycogen
• Glucagon is released when blood glucose is low, converting stored glycogen into glucose
• High blood glucose causes blood plasma and tissue fluid to become too concentrated, potentially damaging cells
• Low blood glucose can cause cells to swell up and burst (lysis)

Human Reproduction - Female

• Ovaries: produce and store ovum, and where estrogen is produced
• Fallopian Tubes (Oviducts): site of fertilization and connecting ovaries to the uterus.
• Uterus: The connection between cervix and external female body parts, is the route for penis during coitus and fetus during delivery.
• Vagina: connects the cervix to the external body, a passageway during childbirth.

Follicle Development

• Primordial Follicle: Contains an oocyte surrounded by granulosa cells and an oocyte nucleus
• Primary Follicle: An oocyte with nucleus surrounded by granulosa cells and zona pellucida forms
• Secondary Follicle: Formation of the Theca layer, a larger follicle with fluid-filled antrum
• Tertiary Follicle: A fully grown oocyte, surrounded by multiple granulosa cell layers, and has the presence of Theca cells
• Ovulation: Primordial follicles mature to primary, secondary, and tertiary follicles within the ovary
• Secondary Oocyte structure: Has Corona radiata, zona pellucida, nucleus, polar body and plasma membrane

Oogenesis

• Oogenesis: Begins during fetal development and has three stages
• Primary oocyte: Formed before birth, suspended until puberty
• Secondary oocyte: Is released during ovulation
• Mature ovum: Formed after fertilization

Male Reproductive System

• Testicles (Testes): Where sperm and testosterone are produced
• Scrotum: Houses testicles, and maintains temperature for sperm production
• Vas Deferens: Transports mature sperm from the epididymis to the urethra
• Accessory Glands: Seminal vesicles, prostate gland, and Cowper’s gland produce semen
• Penis: Delivers sperm through the vaginal canal during intercourse

Spermatozoa

• Life days in man: 64 days
• First meiosis: 16 days
• Second meiosis: 16 days
• Spermatogenesis: 24 days
• Lifespan after ejaculation: 24-48 hours
• Normal sperm count: 1200-300 million/milliliter
• Normal amount: 2-5 milliliters
• Oligospermia: low sperm count (>20 million/milliliter)
• Azoospermia: no sperm count

Spermatogenesis and Oogenesis

• Spermatogenesis has four steps
  • Proliferation divides by mitosis into two daughter spermatogonia
  • Growth where spermatogonia enlarge into primary spermatocytes
  • Maturing contains four stages, primary spermatocytes form secondary spermatocytes. Secondly spermatocytes pass for meiosis II, forming spermatids, which leads to a mature sperma.
  • Mature sperma contains with Haploid, consists of head, midpiece and tail

Spermatogenesis vs Oogenesis

• Spermatogenesis
  • Number of gametes: millions throughout lifetime
  • Timing of Formation: Continuous
  • Timing of release: Anytime
  • Begins/Ends: In puberty, through whole life
  • Meiotic division: uninterrupted
  • Where occurs: tests and leads to the formation of sperms
• Oogenesis
  • Number of gametes: Fixed only about 400 mature
  • Timing of Formation: menstrual cycle once a month
  • Timing of release: Monthly Cycle
  • Begins/Ends: During fetal development, menopause
  • Meiotic division: arrested
  • Where occurs: ovary and leads to the production of the ova

Entamoeba histolytica and Malaria

• Entamoeba histolytica life cycle involves ingestion of mature cysts from contaminated sources, excystation releasing trophozoites migrating the large intestine where they can be non-invasive or invade the intestinal mucosa multiplying by binary fission creating cysts in feces.
  • Complications include amebic colitis, chronic infections peritoneal and amebomas, liver abscesses
• Malaria, transmitted by a bite of an infected female Anopheles mosquito injecting sporozoites into the bloodstream; in humans, asexual reproduction occurs as sporozoites enter the liver undergoing Schizogony forming merozoites infecting red blood cells. In mosquitoes, gametocytes form zygotes and develop into ookinetes and oocysts releasing sporozoites that migrate to the mosquito’s salivary glands,