D3.2 Inheritance Study Notes
D3.2 Inheritance
Guiding Questions
General Concepts:
What patterns of inheritance exist in plants and animals?
What is the molecular basis of inheritance patterns?
Linking Questions
Effective Sampling in Biological Research:
What are the principles of effective sampling in biological research?
Biological Processes:
What biological processes involve doubling and halving?
D3.2.1 Diploid and Haploid Cells
Definition of Diploid:
A nucleus that has chromosomes organized into pairs of homologous chromosomes.
Most cells are diploid; exceptions include gametes (haploid).
Haploid (n):
Represents one single chromosome from each pair.
In humans, haploid number is , thus diploid cells are .
Exceptions:
Male bees, wasps, and ants are examples of haploid organisms.
D3.2.2 Methods for Conducting Genetic Crossings in Flowering Plants
Gregor Mendel's Experiments (1865):
Conducted experiments with pea plants, observing how traits are passed down.
Used term “factor” in place of “gene” since DNA was not discovered.
Artificial Pollination Techniques:
Deliberately placed pollen from the male part of one flower to the female part of another.
Used brushes for pollination and covered flowers to avoid interference from pollinators.
Results Observed by Mendel
Observed ratios, close to in all traits studied.
Initial Crosses:
Crossed purebred tall plants with purebred short plants.
Result: 100% tall plants, as the allele for tall plants is dominant over that of short plants.
D3.2.3 Alleles and Genotype
Definition of Alleles:
Different versions of a gene differing by one or a few bases.
Example: Two alleles for height: tall vs. short.
Genotype:
Symbolic representation of an organism’s alleles, e.g., BB, GG, tt.
Homozygous:
Two identical alleles (dominant or recessive).
Heterozygous:
Two different alleles (one dominant, one recessive).
Carrier:
Individual with a recessive allele that doesn't impact phenotype.
D3.2.4 Phenotype Definitions
Phenotype:
Observable traits (e.g., blue eyes, type A blood).
Influenced by genotype and environmental factors.
Potential Questions:
Examples of purely genetic phenotypes vs. environmentally influenced phenotypes.
Examples:
Exclusively genetic: ABO blood type, color blindness.
Exclusively environmental: Learned behaviors.
Interaction: Height, Cancer.
D3.2.5 Dominant and Recessive Alleles
Dominant Allele:
Expressed in phenotype, regardless of pairing (same or different).
Recessive Allele:
Expressed only when dominant allele is absent ('masked').
Codominant Alleles:
Pairs of alleles that both affect phenotype in a heterozygote.
D3.2.6 Phenotypic Plasticity
Definition:
The ability to express different phenotypes based on environmental conditions.
Can involve physiological, morphological, or behavioral changes.
Examples:
Birds increasing digestive enzymes during food shortages.
Snails altering shell shape in response to predation cues.
Plants changing leaf thickness in different light conditions.
D3.2.7 Phenylketonuria (PKU)
Definition:
A recessive genetic condition due to mutations in the PAH gene affecting phenylalanine metabolism.
High phenylalanine can be toxic and affect brain development.
Management:
Diet excluding high phenylalanine foods required.
Alleles for PAH:
Dominant allele (F): Produces PAH
Recessive allele (f): No PAH production.
D3.2.9 ABO Blood Types and Multiple Alleles
ABO System Variations:
Alleles: .
Phenotypes: A, B, AB, O.
Codominance present between $ I^{A} $ and $ I^{B} $.
Punnett Square Exercises:
Demonstrate the use of Punnett squares to calculate probabilities of blood type inheritance.
D3.2.10 Incomplete Dominance and Codominance
ABO Blood Groups Analysis:
Codominance observed; both antigens present.
Incomplete Dominance Example:
Flower color in four o’clock plant where heterozygotes show intermediate phenotypes.
D3.2.11 Sex Determination in Humans
Sex Chromosomes in Humans:
XX for females, XY for males; determine reproductive structures.
Probability of Gender in Offspring:
50% chance for boy or girl.
Implications of Mutations on X Chromosome:
X-linked genes can affect sexes differently due to their distribution in gender chromosomal arrangements.
D3.2.12 Hemophilia and Related Disorders
Definition:
A recessive sex-linked disorder affecting blood clotting due to faulty coagulation factors on the X chromosome.
Other examples: Color blindness, Duchenne muscular dystrophy.
D3.2.13 Pedigree Charts in Genetics
Usage of Pedigree Charts:
Illustrate biological relationships and inheritance patterns.
Case Studies:
Cystic fibrosis as an autosomal recessive condition example in pedigree analysis.
Distinction between dominant and recessive inheritance illustrated.
D3.2.14 Continuous Variation and Polygenic Inheritance
Distinction between Variation Types:
Discontinuous (single-gene) vs. continuous (multiple genes influencing traits).
Examples of continuous traits: Height, skin color.
Effect of Environmental Factors:
Influence on phenotypic expression (e.g., nutrition affecting height).
D3.2.16 HL Segregation and Independent Assortment
Mendel’s Laws:
Law of Segregation: Each gamete inherits one of two alleles.
Law of Independent Assortment: Inheritance of one trait does not affect another.
D3.2.21 Chi-Squared Test in Genetics
Statistical Analysis:
Used for determining significance between observed and expected results.
Steps in Chi-Squared Analysis:
Identify null and alternative hypotheses.
Construct a comparatory table of frequencies.
Apply chi-squared formula.
Determine degrees of freedom.
Identify p value to interpret significance.
Application of Statistical Tests
Conclusion of Tests:
Test results leading to acceptance/rejection of null hypothesis as applicable in genetic hypothesis testing.
Additional Notes
Pedigree charts and chi-squared tests are valuable tools in genetics for visualizing and understanding inheritance patterns. Links to further reading and exercises on specific topics are attached for enhanced understanding.