Fertilization and Heredity

• Fertilization, also known as conception, occurs when sperm and ovum combine to form a zygote
• The zygote then duplicates through cell division.
• Ovulation is the rupture of a mature follicle in the ovary, expelling an ovum monthly until menopause.
• Dizygotic twins, also called fraternal twins, originate from two separate eggs fertilized by different sperm
• They can be the same or different sexes and may have a genetic basis.
• Monozygotic twins result from the cleaving of one fertilized egg and are genetically identical.
• Heredity is the genetic transmission of heritable characteristics from parents to offspring.
• Deoxyribonucleic Acid (DNA) is a spiraling ladder with steps made of chemical units called bases
• Adenine, Thymine, Cytosine, and Guanine
• Chromosomes are coils of DNA containing smaller segments called genes.
• Mitosis is cell division in non-sex cells.
• Meiosis is cell division in sex cells.
• Mutation is a mistake in copying genetic code that creates permanent alteration in genetic material.
• Autosomes are not affiliated to sexual expression.
• Sex Chromosomes are the 23rd pair that indicates the baby’s sex which is XX for female and XY for male.
• Alleles produce alternative expressions of characteristics.
• Homozygous is when two alleles are the same.
• Heterozygous is when two alleles are different.
• Dominant alleles are always expressed or shows up as a trait in that person.
• Recessive alleles usually do not show unless paired with another recessive trait.
• Polygenetic Inheritance is the interaction of several genes.
• Phenotype is observable characteristics.
• Genotype is underlying genetic makeup.
• Epigenesis is where the environment can influence when and which genes turn on and off
• This refers to chemical molecules attached to a gene that alter the way a cell "reads" the gene’s DNA.
• Cells are susceptible to epigenetic modification during critical periods like puberty and pregnancy.

Chromosomal Abnormalities

• Down Syndrome involves an extra copy of chromosome 21, treated with surgery and SPED.
• Klinefelter Syndrome involves an extra X chromosome (XXY), treated with hormone therapy.
• Fragile X Syndrome involves abnormality in the X chromosome and the cause is ID, treated with SPED and Speech Therapy.
• Turner Syndrome involves a missing chromosome and is treated with hormone therapy.
• Jacob's Syndrome (XXY Syndrome) involves an extra Y chromosome and requires no treatment.

Gene-Linked Abnormalities

• Cystic Fibrosis involves overproduction of mucus in the lungs and digestive tract and is treated with physical therapy.
• Diabetes occurs when the body does not produce enough insulin and is treated with insulin.
• Hemophilia is delayed blood clotting and is treated with blood transfusions.
• Huntington’s deteriorates the central nervous system, producing problems in muscles and mental decline.
• Phenylketonuria involves the build up of Phenylalanine in the body and is treated with a special diet.
• Sickle-Cell Anemia limits body oxygen supply and is treated with Penicillin, Antibiotics, and pain relievers.
• Spina Bifida is an incompletely closed spinal canal that is fixed with surgery.
• Tay-Sachs disease involves an accumulation of lipids in the nervous system and is treated with medication.
• Anencephaly involves the absence of brain tissue and is treated with a special diet.
• Polycystic Kidney Disease involves enlarged kidneys which may need to be treated with a kidney transplant.
• Alpha antitrypsin Deficiency involves cirrhosis of the liver in early infancy that causes death and has no treatment.
• Alpha Thalassemia and Beta Thalassemia both involve severe anemia the frequent need for blood transfusions soon after birth
• Early death can occur from Thalassemia

Prenatal Diagnostic Tests

• Ultrasound Sonography uses high frequency sound waves to create an image to provide information on the fetus
• It does not harm the women or the fetus
• It can detect abnormalities and the sex of the fetus etc
• Fetal MRI uses magnet and radio waves to take images of the fetus' body structure
• Chorionic Villus Sampling takes a small sample of the placenta
• small chance of limb deformity can result
• Amniocentesis takes a sample of the amniotic fluid to check for metabolic and chromosome abnormalities
• Maternal Blood Screening identifies if the pregnancy has an elevated risk of birth defects

Prenatal Development

• Gestation period is between conception and birth and is between 37-41 weeks
• Gestational age is dated from the first day of the last menstrual cycle
• Cephalocaudal Principle of stages of prenatal development is that development progresses head to the lower extremities
• Proximodistal Principle of the stages of prenatal development is that development comes from the center to the outer parts of the body

Early Signs and Symptoms of Pregnancy

Symptoms include:

• Tender and swollen breasts, fatigue, slight bleeding or cramping, food cravings, nausea, headaches etc

Stages of Pregnancy

First: Germinal stage from fertilization lasting 2 weeks

• Zygote undergoes cell division as it travels to fallopian tube