Chapter 8 Summary

• Gregor Mendel, the Father of Genetics. Mendel completed groundbreaking experiments with pea plants in the mid-1800s, revealing fundamental heredity principles and challenging the blending theory of inheritance by showing that traits are inherited as distinct units, not mixed averages of the parents.
• Experiments on Pea Plants. Pea plants were ideal for Mendel’s experiments because they grow quickly, are easy to control for pollination, and have clear contrasting traits (e.g., purple vs. white flowers). True-breeding plants always produce offspring with the same trait when self-pollinated, making them essential for Mendel’s controlled crosses. Cross-pollination between different true-breeding plants led to hybrids in the F1 generation that only showed the dominant trait.
• Law of Segregation. In monohybrid crosses, Mendel observed that the trait that disappeared in the F1 generation reappeared in the F2 generation in a 3:1 ratio, leading to the Law of Segregation:
  • Each organism carries two alleles for each trait.
  • These alleles separate during gamete formation, so each gamete gets only one allele.
• Law of Independent Assortment. In dihybrid crosses, Mendel found that traits are inherited independently of one another, leading to the Law of Independent Assortment:
  • Alleles for different traits segregate independently during the formation of gametes.
• Foundations of Modern Genetics. Mendel’s work formed the foundation of modern genetics, although his ideas were not widely accepted until decades later.
• Non-Mendelian Modes of Inheritance.  Many human traits follow non-Mendelian modes of inheritance, including multiple allele traits, traits with codominance or incomplete dominance, and polygenic traits, and pleiotropy.

---

OpenAI. (2025). ChatGPT. [Large language model]. https://chat.openai.com/chat
Prompt: Summarize the following content into key takeaways.

Heredity – The passing of traits from parents to offspring

Character– A heritable feature that varies among individuals (e.g. flower colour)

Trait – A specific variation of a character (e.g. purple flowers)

Pollination: The transfer of pollen from the male anther to the female stigma of a flower.

True-breeding: Organisms that produce offspring identical to themselves when self-pollinated

Hybrid: Offspring resulting from the cross between parents with different traits

P generation: The parental generation in a genetic cross

F1 generation: The first filial generation, offspring of the P generation

F2 generation: The second filial generation, offspring of the F1 generation

Law of segregation: Mendel’s principle stating that two alleles for a trait separate during gamete formation

Law of independent assortment: Mendel’s principle stating that genes for different traits can segregate independently during the formation of gametes

Genetics – The science of heredity; The study of how traits are passed from parents to offspring

Gene – A section of DNA on a chromosome that codes for a specific protein; Controls a character

Locus – The specific physical location of a gene on a chromosome

Allele – Different versions of a gene; Determines a specific trait

Homologous Chromosomes – A pair of chromosomes that have the same genes at the same loci; One comes from the father and one from the mother

Dominant Allele – An allele that is expressed in the phenotype even when only one copy is present in the genotype (e.g. B for purple flowers)

Recessive Allele -An allele that is only expressed in the phenotype if two copies are present in the genotype (e.g. b for white flowers)

Genotype: The genetic makeup of an organism; consisting of the alleles inherited from its parents

Heterozygous: Having two different alleles for a particular gene

Homozygous: Having two identical alleles for a particular gene

Phenotype: The observable traits of an organism; Determined by its genotype.

Monohybrid Cross – A genetic cross between two individuals that differ in only one character (e.g. seed colour)

Punnett Square – A diagram used to predict the genotype and phenotype ratios of offspring from a genetic cross

Probability – The measure of the likelihood that an event will occur; Calculated by the number of times the event occurs divided by the total number of opportunities for the event to occur

Dihybrid cross – A genetic cross between parents that differ by two characters

Mendelian inheritance: Inheritance of traits controlled by a single gene with two alleles, one of which may be completely dominant to the other

Autosomal traits: Traits controlled by genes on one of the 22 pairs of human autosomes

Sex-linked traits: Traits controlled by genes on the sex chromosomes

Dominant disorder: Genetic disorder caused by a mutated dominant allele; One copy from one parent is sufficient to cause the disorder in the offspring

Recessive disorder: Genetic disorder that occurs when an individual inherits two recessive mutant alleles for a particular gene

Carrier: Individual that does not have the disorder themselves, but they carry the recessive mutant allele so their offspring can inherit it

Pedigree: A diagram that shows the occurrence and appearance of phenotypes of a particular gene or organism and its ancestors across multiple generations

Non-Mendelian inheritance: Inheritance patterns that do not follow Mendel’s laws

Multiple allele traits: Traits controlled by a single gene with more than two alleles

Codominance: A type of inheritance where both alleles in a heterozygote are fully expressed

Agglutination: Clumping of blood cells due to the binding of antigens and antibodies

Incomplete dominance: A type of inheritance where the phenotype of a heterozygote is intermediate between the phenotypes of the homozygous parents

Polygenic inheritance: The inheritance of traits controlled by multiple genes, often resulting in a continuous range of phenotypes.

Pleiotropy: A single gene influencing more than one phenotypic trait

Father of Genetics: Gregor Mendel

Plants Mendel studied? Pea plants

Why study pea plants? Fast-growing, easy to raise, have several different characters, self-pollinating

Mendel’s Laws: Law of segregation and law of independent assortment

AA – homozygous dominant genotype

Aa – heterozygous genotype

aa – homozygous recessive genotype

Why are recessive sex-linked traits more common in men? Men have only one X chromosome, so a single recessive allele will express the trait

Non-Mendelian modes of inheritance: multiple alleles traits, codominance, incomplete dominance, polygenic traits, pleiotropy

Blood Type O: Universal donors because their blood lacks A and B antigens; Causes no immune reaction when transfused into others

---

OpenAI. (2025). ChatGPT. [Large language model]. https://chat.openai.com/chat
Prompt: Can you give me brief summaries of these key terms