Comprehensive Notes on Hereditary Influences

Page 1: Hereditary Influences

• Overview: Hereditary influences pertain to how genetic factors are transmitted from parents to offspring and contribute to development, traits, and disorders.

Page 2: Definition of terms

• Genotype: the genes that one inherits
• Phenotype: one’s observable or measurable characteristics
• Conception: the moment when an ovum released by a woman’s ovary and on its way to the uterus via the fallopian tube is fertilized by a man’s sperm

Page 3: DIFFERENCE BETWEEN GENOTYPE AND PHENOTYPE

• GENOTYPE
  • The genetic makeup of an organism, representing the specific combination of genes and alleles it inherits from its parents.
• PHENOTYPE
  • The observable traits and characteristics of an organism, which result from the interaction between its genotype and the environment.

Page 4: The Genetic Material

• After fertilization, a protective biochemical reaction repels other sperm, preventing fertilization by additional sperm.
• Within hours, the sperm’s genetic material is released as the sperm disintegrates.
• The ovum releases its genetic material, and a new cell nucleus forms around the hereditary information from both parents.
• The new cell is a zygote, which is $rac{1}{20}$ the size of the head of a pin, yet contains the material for development from a single cell into a complete human being.

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Page 6: What is Zygote?

• Zygote: the fertilized egg that results from conception.
• Fertilization: the process that forms the zygote.
• Zygote: the product of fertilization (conceptual shorthand shown as "ƏG").

Page 7: The Genetic Material

• The human zygote’s nucleus contains $46$ chromosomes.
• Each chromosome consists of thousands of chemical segments, or genes—the basic units of heredity that build proteins.
• One member of each chromosome pair comes from the mother’s ovum and the other from the father’s sperm cell.
• Thus, each parent contributes $23$ chromosomes to each child.
• Genes on each chromosome function as pairs; the two members of each gene pair occupy the same sites on their corresponding chromosomes.
• Genes are stretches of deoxyribonucleic acid (DNA), a double-helix molecule that provides the chemical basis for development.

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• (Illustrations/diagrams referenced; content not text-based in the transcript.)

Page 10: Growth of the Zygote and Production of Body Cells

• The zygote moves toward the uterus and replicates via mitosis.
• Initial divisions: $2$ cells, then $4$, $8$, $16$, and so on.
• Before each division, the cell duplicates its $46$ chromosomes; the duplicate sets move in opposite directions.
• By birth, the individual comprises billions of cells formed via mitosis that become muscles, bones, organs, and other structures.
• Mitosis continues throughout life, generating new cells for growth and replacing damaged cells.

Page 11: Embryonic Development Timeline (Mitotic Stages)

• Zygote (Conception, day 0)
• 2-cell stage (≈ day $1.5$)
• 4-cell stage
• 16-cell morula (≈ day $3$)
• 58-cell blastocyst (≈ day $4$)
• 107-cell unilaminar blastocyst (≈ day $4.5$)
• Partially implanted early bilaminar blastocyst (≈ day $6$)
• Stages occur within the uterine environment including uterine gland, mucosa, and wall interactions
• Key terms: zygote, pronuclei stage, polar body, conception (0 days)

Page 12: The Germ or Sex Cells

• Germ cells exist to produce gametes (sperm in males, ova in females).
• Meiosis reduces chromosome number to the haploid set in gametes.
• The germ cell first duplicates its $46$ chromosomes.
• Crossing-over often occurs: adjacent duplicated chromosomes cross and exchange segments, creating new and unique hereditary combinations.
• This exchange contributes to genetic diversity in offspring.

Page 13: GERM CELLS terminology

• female germ cell, male germ cell
• segregation via meiosis
• GERM CELLS: egg, sperm
• diploid vs. haploid gametes (gametes are $1$ set of chromosomes, i.e., haploid; body cells are diploid, $2$ sets)

Page 14: Sex Chromosomes (XX, XY)

• XX represents female; XY represents male. (XX on one side; Y appears on the other side in the male case.)

Page 15: Hereditary Uniqueness

• When chromosome pairs segregate during meiosis, it is a matter of chance which chromosome ends up in a given gamete.
• Independent assortment means many different chromosome combinations can result from meiosis of a single germ cell.
• Humans have $23$ chromosome pairs, so each parent can produce $2^{23}$—more than $8{,}000{,}000$—different genetic combinations in their sperm or ova.

Page 16: Multiple Births – Monozygotic Twins

• Monozygotic (identical) twins: two individuals developed from a single zygote that split into separate but identical cells.
• Occurrence: about $rac{1}{250}$ of births worldwide.
• Because they are genetically identical, monozygotic twins should show very similar developmental progress if genes heavily influence development.

Page 17: Multiple Births – Dizygotic Twins

• Dizygotic (fraternal) twins: about $rac{1}{125}$ of births.
• They arise when a mother releases two ova at the same time and each is fertilized by a different sperm.
• Fraternal twins are not more genetically similar than ordinary siblings.

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Page 19: Male or Female – Sex Determination

• Normal human karyotypes show autosomes (22 pairs) that are similar in males and females.
• The 23rd pair determines sex: males have XY; females have XX.
• Sex is determined by the sperm that fertilizes the ovum: X-bearing and Y-bearing sperm are produced in roughly equal quantities; ova contain only X.
• Therefore, the child’s sex depends on whether an X-bearing or a Y-bearing sperm fertilizes the ovum.
• Note: The transcript mentions social and biological injustices with sex determining roles; this reflects a historical viewpoint highlighted in the source.

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Page 21: What do genes do?

• At a basic biochemical level, genes call for the production of amino acids, which form enzymes and other proteins necessary for forming and functioning of new cells.
• Example: Genes regulate the production of melanin in the iris of the eye.
• Genes guide cell differentiation, specifying which cells become parts of the brain, central nervous system, circulatory system, bones, skin, etc.
• Genes influence and are influenced by the biochemical environment during development; environmental influences combine with genetic influences to determine how a genotype translates into a phenotype.

Page 22: How are genes expressed?

• Simple Dominant-Recessive Inheritance: Many human characteristics are influenced by one gene pair (alleles): one from each parent.
• Codominance: The phenotype produced is a compromise between the two genes (e.g., blood types A and B are equally expressive; neither dominates the other).
• Sex-Linked Inheritance: Some traits are determined by genes on the sex chromosomes.

Page 23: Hereditary Disorders

• Approximately 5% of newborns have a congenital problem.
• Congenital defects are present at birth, though many are not detectable at birth.

Page 24: Chromosomal Abnormalities

• Meiosis occasionally distributes 46 chromosomes unevenly among gametes.
• One gamete may have too many or too few chromosomes.
• Most chromosomal abnormalities conceived are lethal and fail to develop or are spontaneously aborted.

Page 25: Chromosome Abnormalities (Genomic changes)

• Deletion, Duplication, Substitution, Inversion, Translocation (structural changes in chromosomes).
• The content shows sequences and examples of chromosomal segments and mutations (illustrative genetic material).

Page 26: Abnormalities of the Sex Chromosomes

• Sex-chromosome abnormalities include various extra or missing sex chromosomes: XXY, XYY, XO, XXX, etc.
• Conditions listed:
  • Turner’s syndrome; XO
  • Poly-X or superfemale (XXX, XXXX, XXXXX)
  • Klinefelter’s syndrome; XXY or XXXY
  • Supermale or Jacob’s syndrome; XYY, XYYY, XYYYY

Page 27: Turner’s Syndrome (XO)

• Missing an X chromosome on the 23rd pair.
• Features include: short stature, low hairline, shield-shaped thorax, widely spaced nipples, short metacarpal IV, small finger nails, brown spots (nevi), fold of skin on the neck, constriction of the aorta, poor breast development, elbow deformity, rudimentary ovaries, gonadal streaks, and no menstruation.

Page 28: Triple X Syndrome

• Main symptoms: above-average height, delayed speech development, mild intellectual disabilities, menstrual irregularities, premature ovarian failure.
• Not all symptoms are listed; severity varies between individuals.

Page 29: Klinefelter Syndrome

• Main symptoms: psychomotor delays and learning difficulties, tall stature, enlarged breast tissue and increased belly fat, small penis and testes, reduced facial and body hair and muscle mass, azoospermia.
• Not all symptoms are listed; severity varies between individuals.

Page 30: Jacobs Syndrome

• Main symptoms: taller than average, severe acne, behavioral problems, possible reading and language difficulties, mild developmental delay.

Page 31: Genetic Abnormalities (Examples)

• 1. Cystic fibrosis: a genetic disease causing thick mucus buildup affecting lungs, pancreas, and other organs; can impair breathing and nutrition.
• 2. Diabetes: elevated blood glucose due to insufficient insulin production or response.
• 3. Duchenne-type muscular dystrophy: progressive skeletal and heart muscle weakness; commonly begins ~age 6; currently no cure.
• 4. Hemophilia: rare inherited bleeding disorder with reduced blood clotting.

Page 32: Genetic Abnormalities (continued)

• 5. Phenylketonuria (PKU): lack of an enzyme needed to break down a specific amino acid; amino acid buildup can be toxic in blood and brain without treatment.
• 6. Sickle-cell anemia: mutation causing abnormal crescent-shaped red blood cells; cells are stiff and can block vessels; leads to severe anemia.
• 7. Tay-Sachs disease: genetic condition causing progressive nerve cell damage and death in brain and spinal cord.

Page 33: Predicting Hereditary Disorders

• Genetic counseling helps prospective parents assess the likelihood that their children will be free of hereditary defects.
• Process typically begins with collecting a complete family history (pedigree) to identify relatives affected by hereditary disorders.
• Pedigrees are used to estimate the likelihood that a couple will bear a child with a chromosomal or genetic disorder; for some disorders, pedigrees may be the only basis for risk assessment (e.g., certain diabetes forms, some muscular dystrophies).

Page 34: Detecting Hereditary Disorders

• Prenatal screening becomes more common as maternal age increases, due to higher chromosomal abnormality risk after age 35.
• Amniocentesis: a large, hollow needle withdraws a sample of the amniotic fluid surrounding the fetus for testing.
• Chorionic villus sampling (CVS): tissue sampling for the same tests as amniocentesis, performed in the 8th or 9th week of pregnancy.
• Ultrasound (sonography): uses sound waves to scan the womb; considered very common and very safe prenatal diagnostic technique, most useful after the 14th week of pregnancy.