Genetics Quiz: Blood Types and Inheritance Patterns

Mendel and the Gene Idea

• Johann Gregor Mendel, trained in science at the University of Vienna, was a monk.
• Mendel's work preceded the understanding that both parents contribute to offspring characteristics.
• The prevailing theory at the time was the blending theory of heredity.
• Modern genetics began with Mendel's work, replacing the blending theory with the particulate theory of heredity.
• Mendel's teachers included a physicist (Doppler) who taught him quantitative experimental approaches and a botanist (Unger) who sparked his interest in inheritable variation in plants.
• Mendel studied garden peas due to their many different characteristics and traits.

Pea Plant Characters and Traits

• Mendel observed seven characteristics in pea plants:
  • Flower color (purple or white)
  • Flower position (axial or terminal)
  • Seed color (yellow or green)
  • Seed shape (round or wrinkled)
  • Pod shape (inflated or constricted)
  • Pod color (green or yellow)
  • Stem length (tall or dwarf)

Mendel's Findings

• Mendel's experiments involved true-breeding plant varieties.
• Key terms:
  • P generation: Parental generation
  • F₁ generation: First filial generation
  • F₂ generation: Second filial generation

Mendel's Conclusions

• Mendel developed two principles of heredity:
  • The Law of Segregation: Two alleles for a character are packaged into separate gametes.
  • The Law of Independent Assortment: Two alleles for different characters are packaged into gametes independently.
• In a monohybrid cross, observed traits (like flower color) do not blend. Observed ratios in the following generations indicated that the white trait wasn't lost, the allele for white color was masked by the purple allele. This led to the idea of one allele being dominant and another being recessive.
• Mendel's experiments showed a consistent 3:1 ratio for the traits in the F₂ generation - with one dominant allele and one recessive allele.

Mendel's Model

• Alternative forms of genes (alleles) are responsible for variations in inherited traits.
• For each character, an organism inherits two alleles (one from each parent).
• If the alleles differ, one is dominant (fully expressed), while the other is recessive.
• The alleles segregate during gamete production.

Segregation and Recombination

• The white allele was not lost but masked by the presence of the purple allele.
• Mendel found that the purple flower trait was dominant and the white flower trait was recessive.
• Similar ratios of 3:1 were evident in subsequent traits.

Genotype vs. Phenotype

• Genotype refers to the genetic makeup of an organism (e.g., AA, Aa, aa).
• Phenotype refers to the observable traits (e.g., purple flowers, white flowers).

Determining Heterozygosity

• Test crosses and back crosses can be used to determine genotypes.

Independent Assortment

• In dihybrid crosses, Mendel crossed parental varieties that differed in two traits at a time.
• Results showed a 9:3:3:1 phenotype ratio. This established independent assortment.

Mendelian Inheritance and Probability

• Mendelian inheritance follows the rules of probability.
• The probability of an event occurring can range from 0 to 1.

Intermediate Inheritance

• Sometimes the heterozygous genotype results in an intermediate phenotype.
• Not blending of phenotypes, the effects of alleles are not masked or hidden by each other.

Multiple Alleles

• A gene may have more than two allele forms.
• The ABO blood group is an example.

Epistasis

• One gene affects the expression of another gene.

Polygenic Inheritance

• Multiple loci (genes) can influence a single trait.
• Traits with a continuous range of variations (e.g., skin pigmentation) are likely to be polygenic traits.

Pleiotropy

• One gene can affect multiple traits.
• Sickle cell anemia is an example.

Environmental Impact on Phenotype

• Environmental factors can influence phenotype expression; the phenotypic range of a genotype is known as the norm of reaction.

Test your knowledge on genetics with this quiz focusing on blood types, inheritance patterns, and key genetic concepts like pleiotropy and codominance. Answer questions about genotypes, probabilities, and the historical context of genetics. Perfect for students studying genetics!