GENETICS 🧬

• MEIOSIS, DEVELOPMENT, AND AGING & TRANSMISSION GENETICS: SINGLE GENE INHERITANCE
• Reproductive system

  The source of the body's most specialised cells
• Reproductive system

  • Consists of reproductive organs such as the testes, penis, vagina, ovaries and etc.
  • Ensures a species' survival through sexual reproduction
  • Main job is to simply produce offspring, however other organ systems assist in this task as well
• Key functions of the reproductive system


  • To Produce Egg and Sperm Cells (Gametes)
  • To Transport and Sustain these cells
  • To Nurture the Developing Fetus
  • To Produce Hormones Needed For Sex Characteristics
• Male reproductive system


  • The superficial organs are the penis, scrotum, testicles, and epididymis
  • The deep organs produce important fluids that are released alongside semen and help produce necessary hormones for growth

  
• Female reproductive system


  • The main organs consist of the ovaries, fallopian tubes, uterus, and cervix
  • Responsible for producing essential hormones such as estrogen and progesterone
• Meiosis


  • A type of cell division found only within eukaryotic organisms that enable the synthesis of gametes
  • Occurs in the reproductive organs of the male and female
  • Necessary for human beings because it ensures that new offspring contain all necessary chromosomes

  
• Meiosis I

  Homologous chromosomes pair up and exchange genetic material through crossing over in a process called recombination
• Meiosis II

  Sister chromatids, which were produced during Meiosis I, separate from each other, resulting in the formation of four haploid daughter cells
• Gamete Maturation/Gametogenesis

  • The process of the germ cell maturing into mature gametes; that can function as sperm and egg cells
  • Regulated by hormones in the body and occurs through meiotic division
  • Divided into Spermatogenesis (for sperm) and Oogenesis (for eggs)

  
• Prenatal Development

  • The process from conception to birth, where a single cell or the Zygote goes from a single cell to a fully formed Fetus
  • Covers 3 stages: Germinal (0-2 weeks), Embryonic (3-8 weeks), Fetal (9 weeks up until birth)

  
• Birth Defects

  • Structural changes present at birth that can affect almost any part or parts of the body (e.g., heart, brain, foot)
  • May affect how the body looks, works, or both
  • Can vary from mild to severe
• Chromosomal Abnormalities

  • Genetic causes of many birth defects determined during the nuclear events of fertilization
  • Trisomy 21 (Down syndrome), trisomy 13 (Patau syndrome), and trisomy 18 (Edwards syndrome) are the most frequent birth defects
• Maturation

  • The main oocyte's maturation division differs substantially from the spermatocyte's maturation division
  • The cytoplasm of the oocyte divides unequally after meiotic division of the nucleus to generate a single big haploid egg and three little haploid polar bodies or polocytes

  
• Spermatogenesis

  • The process through which sperms are produced in the testicular seminiferous tubules
  • Germinal epithelial cells line the seminiferous tubules, including cuboidal primary or primordial germ cells (PGCs) and tall somatic cells known as Sertoli cells (= nurse cells)
• Aging

  • The decay of an organism's structure and function, in which molecular and cellular modifications can have various effects at the individual level over the course of a lifetime
  • The accumulation of molecular errors that compromise adult stem cell functions occurs because of genetic and epigenetic interactions and depends on hereditary, environmental, and stochastic factors
• Monohybrid Cross

  • Discovered by Gregor Mendel in the mid 19th Century studying pea plants
  • Mendel observed that different alleles could affect a single trait separately and remained indivisible, and that an allele might be present but invisible in one generation, only to reappear in the next
• Single-Gene Inheritance

  • Traits controlled by a single gene with 2 alleles, one allele being dominant to the other
  • Inheritance patterns can be controlled by genes on autosomes (autosomal traits) or sex chromosomes (sex-linked traits)
  • Example: Widow's peak, eye color, freckles, hairline etc.
• Single-Gene Inheritance is Rare
• Rarity of Single-Gene Inheritance

  • Compounded by the vast number of genes and alleles in the human genome
  • New mutations on 1 chromosome contribute to the rarity
  • Single-gene disorders are heterozygous in nature
• Following the Inheritance of More than One Gene

  • Involves understanding how multiple genes interact and contribute to the inheritance of traits
  • Genes are units of heredity that code for specific traits
  • Inheritance of traits is not always determined by a single gene, many traits are influenced by multiple genes interacting together
• Polygenic Inheritance

  • Involves the interaction of multiple genes to determine a single trait
  • Occurs when multiple genes contribute to the expression of a single trait
  • Each gene may have different alleles, and the combined effect of these alleles results in a wide range of phenotypic variations
• Human Skin Color

  • Several genes, such as MC1R, SLC24A5, and TYR, contribute to skin pigmentation
  • Different combinations of alleles from these genes result in varying skin tones among individuals
• Following the inheritance of more than one gene is crucial for understanding the complexities of genetic inheritance
• Pedigrees are utilized for studying the inheritance pattern of a specific trait across generations within a family
• Pedigrees

  • Depict whether a trait is present or absent concerning the familial connections between parents, offspring, and siblings
  • Employ standardized symbols to depict family members and their relationships
  • Through pedigree analysis, we can ascertain genotypes, recognize phenotypes, and forecast the inheritance pattern of a trait