Genetics exam 1

• Genetics


  The study of heredity and the variation of inherited characteristics
• Genetics is relevant for diagnosis of genetic diseases, gene therapy, vaccine development, and genome sequencing
• Diagnosis of Genetic Diseases

  • Early detection enables prompt medical interventions
  • PKU screened in babies
  • Genetic markers for cancer (BRCA1 & BRCA2 genes for breast cancer) to manage and prevent different cancers
• Gene Therapy


  • In 2023, first FDA approved CRISPR therapy for sickle cell
• Vaccine Development


  • RNA based vaccines
• Genome Sequencing


  • Bioinformatics
• Manufacture of mRNA vaccine

  1. Manufacture (synthetically) the target spike protein gene

  2. Insert into a plasmid

  3. Produce mRNA (in Vitro) with RNA polymerase
• Blending hypothesis


  Traits from parents are thought to blend in offspring
• Limitations of blending hypothesis

  • Loss of variation
  • Irreversibility (once traits are blended, they cannot be separated)
• Mendel's choice of experimental subject

  • Easy to cultivate
  • Short generation interval
  • Produce many offspring
  • Large varieties of pea were available to Mendel
  • They differed in various traits
  • They were genetically pure
• Mendel's choice of characteristics

  • 2 easily differentiated forms (yellow & green)
  • Pure lines or true breeding
• Mendel's experiments with a single trait

  1. Crossing pure lines that differed in just one trait (monohybrid cross)

  2. Inheritance of a single trait by mating true breeding individuals from two parent strains

  3. Phenotypic ratio 3:1

  4. Genotypic ratio 1:2:1
• Homozygotes


  Pure breeding lines, contain two copies of the same allele
• Heterozygote


  Contain two different alleles
• Principle of Segregation (Mendel's 1st law)


  Each individual (diploid organism) possesses two alleles for any particular characteristic. These two alleles segregate when gametes are formed, and one allele goes into each gamete
• Dominant and Recessive Traits

  Phenotype 1 is dominant over Phenotype 2 if the F1 of pure breeding strains show Phenotype 1
• Test Cross


  A genetic cross used to determine the genotype of an individual that shows a dominant trait by mating with a homozygous recessive
• Segregation


  Physical separation of alleles during meiosis
• Dihybrid Cross


  1. Mendel crossed varieties of peas that differed in two characteristics (e.g. yellow:green, round:wrinkled)

  2. Frequencies of F2 phenotypes can be predicted by the product law (probability of two or more independent events occurring simultaneously)
• Independent Assortment


  Alleles of different genes are transmitted independently of one another
• Chromosomal basis of Independent Assortment

  • Different chromosomes assort independently at the first division of meiosis
  • The unpaired chromosome was found to go to either pole equally frequently
• Chi-square Test


  • A statistical method used to determine whether observed data (O) deviates significantly from expected data (E)
  • Allows for inference of underlying genetic mechanisms
  • Null Hypothesis (H0): No significant difference between observed and expected data
  • Alternative Hypothesis (H1): Significant difference between observed and expected data
  • Significance level (α) is the predetermined threshold for accepting or rejecting the null hypothesis (commonly set at α = 0.05)
• Sex Determination


  • The process by which an organism develops as male or female
  • Various mechanisms exist across different species, including genetic, chromosomal, environmental, and social factors
• Chromosomal Sex Determination


  • Involves the presence or absence of specific chromosomes (XX female, XY male)
  • 1:1 sex ratio
• Other Sex Determination Systems

  • Birds, snakes, butterflies, some amphibians, fish (ZW female, ZZ male)
  • Bees, wasps, ants (haploid set male, diploid set female)
  • Genic sex determining system (no sex chromosomes, only sex determining genes)
• Environmental Sex Determination


  • Temperature determines sex (e.g. warmer temperature favors one sex in turtles and alligators)
• Social Sex Determination


  • Social interactions or hierarchy can influence sex determination in some species (e.g. clownfish, some frogs)
• Sex Determination in Humans

  • XX female, XY male
  • Turner syndrome (XO, no paired chromosome)
  • Klinefelter syndrome (XXY, XXXY, XXXXY, XXYY)
• Dosage Compensation


  Mechanism that compensates for the difference in the number of gene copies between males and females in organisms with sex chromosomes
• X Inactivation in Placental Mammals

  • Early in development, one of the two X chromosomes in each female somatic cell is randomly inactivated
  • The inactive X chromosome is visible as a condensed Barr body
  • Once X inactivation has occurred, it is permanent in all the descendants of that cell
  • Female mammals are mosaics of two populations of cells, one expressing the maternal X and the other expressing the paternal X
• Mechanism of X Inactivation

  Random X inactivation requires an X-linked gene called Xist (X-inactivation specific transcript) that produces large RNA molecules that spread out and cover the chromosome to be inactivated