CYTOGENETI

• Key topics


  • TRANSMISSION
  • GENETICS
  • HEREDITY
  • RECALL
• Genes


  • A unit of heredity passed from parent to offspring
  • Technically: a distinct set of nucleotides within the chromosome that, when transcripted, allows/prevents for the synthesis of a particular amino acid chain (or protein)
  • Genes dictate the expression of specific traits for hair/eye color, height, weight, etc.

  
• Locus


  The specific location of a gene in a chromosome

  
• Locus examples


  • CFTR gene is found in 7q31.2
  • HLA gene 6p21.1-21.3
  • PWCR 15q11.2-q13.1

  
• Alleles


  Variants of the same gene
• Allele example


  • The bey2 gene is a one of the gene pairs that dictates eye color. The dominant allele (BB/Bb) is for brown eyes, while the recessive allele (bb) is for blue eyes.
• Typically, more than one gene affects the manifestation of a trait
• Genotype


  The specific set of genes inherited
• Homozygous


  Both alleles of an organism are the same
• Heterozygous


  The alleles are different
• Phenotype


  The trait that manifests or appears
• Genotype can allow for the development of traits


  But much of a person's phenotype can be affected outside of genetics
• Genotype vs Phenotype examples

  • Genotypic predisposition to a bodybuilder physique, but phenotype of obesity and unhealthiness due to sedentary lifestyle and poor diet
  • Inheriting genes for tallness, but stunted growth from malnutrition
  • Taking height supplements but not reaching full genetic potential
• Mendel's Laws


  The principles of genetics established by Gregor Mendel
• Mendel's Laws


  • Law of Segregation
  • Law of Independent Assortment
• Law of Segregation


  Each individual organism possesses two alleles that can encode a characteristic, and these alleles segregate when gametes are formed, with only one allele going into each gamete
• Mendel's Crosses

  1. Monohybrid cross

  2. P (parental) generation

  3. F1 (filial) generation

  4. F2 generation
• Dominance


  The R allele is the dominant allele, which is often manifested. The r allele is the recessive allele, which is masked or suppressed in the presence of a dominant allele.
• Law of Independent Assortment

  The alleles of two (or more) different genes get sorted into gametes independently of one another
• Law of Independent Assortment examples

  • The gene for seed shape (R/r: round or wrinkled) is assorted independently from other genes such as color (Y/y: Yellow or green), or plant height (T/t: tall or short)

  
• Punnett Square


  Used to predict the outcomes of genetic crosses between two parents

  
• Punnett Square examples


  • Monohybrid cross for seed shape
  • Dihybrid cross for seed shape and color

  
• Branch Diagram


  A convenient way of organizing all the combinations of characteristics in a genetic cross

  
• Testcross


  Used to identify the probable genotype of a parent

  
• Probability Method


  Used to calculate the probability of a specific phenotype occurring by multiplying the probabilities of each individual characteristic
• Gene Interactions


  • Allelic gene interaction
  • Non-allelic gene interaction
• Complete Dominance


  Two different homozygote phenotypes are expressed, either the dominant (DD) or the recessive (dd). A heterozygote genotype (Dd) would express the dominant homozygote phenotype.
• Incomplete Dominance


  A heterozygous phenotype occurs, intermediate between the two parent phenotypes
• Codominance


  Both alleles are fully expressed in the phenotype

  
• Genetic concepts


  • Epistasis
  • Variable expressivity
  • Penetrance
  • Anticipation
• Dominance


  Not all characteristics exhibit dominance. Most genes are expressed through genes that are dominant and recessive. But some genes allow for variations:
• Complete dominance


  • Two different homozygote phenotypes are expressed, either the dominant (DD) or the recessive (dd). A heterozygote genotype (Dd) would express the dominant homozygote phenotype
• Incomplete dominance


  • A heterozygous phenotype occurs
• Incomplete dominance


  • Crossbreeding a red-petaled flower with a white-petaled flower results in a pink phenotype
• A 1:2:1 phenotypic ratio is observed in the progeny with incomplete dominance</b>
• The genotypic ratios and phenotypic ratios of the offspring are the same with incomplete dominance, because each genotype has its own phenotype
• Codominance


  Both alleles are expressed simultaneously
• Codominance


  • ABO blood type in humans
• Multiple alleles


  Diploid species like humans can have more than two alleles for a gene

  
• Multiple alleles


  • ABO blood group has IA, IB, and the amorph allele i