What is meant by the chromosomal basis of inheritance?
Genes are located on chromosomes, and the behaviour of chromosomes during meiosis explains how alleles segregate and assort to produce inheritance patterns observed by Mendel.
What is the diploid chromosome number in humans and what does it represent?
Humans are diploid with 2n = 46 chromosomes, representing two sets of chromosomes—one maternal and one paternal.
What is the haploid chromosome number in humans and where is it found?
The haploid number is n = 23 chromosomes and is found in gametes (sperm and eggs).
What are homologous chromosomes?
Homologous chromosomes are pairs of chromosomes of the same type, one inherited from each parent, carrying the same genes at the same loci but potentially different alleles.
What is the purpose of mitosis and what is its outcome?
Mitosis is used for growth, repair, and maintenance, producing two genetically identical diploid daughter cells.
What is the purpose of meiosis and what is its outcome?
Meiosis produces gametes for sexual reproduction, generating four genetically different haploid daughter cells.
What happens during meiosis I and why is it important?
Homologous chromosomes separate during meiosis I, halving the chromosome number; this is called reductional division.
What happens during meiosis II and how does it compare to mitosis?
Sister chromatids separate during meiosis II, an equational division that is mechanistically similar to mitosis.
How does independent assortment generate genetic variation?
During meiosis, maternal and paternal chromosomes assort independently into gametes, producing many different chromosome combinations.
Why does independent assortment alone underestimate genetic variation?
Because chromosomes themselves are mixtures of maternal and paternal DNA due to crossing over.
What is crossing over and when does it occur?
Crossing over is the exchange of DNA between non‑sister chromatids of homologous chromosomes during prophase I of meiosis.
What is the genetic consequence of crossing over?
It produces recombinant chromosomes containing new combinations of maternal and paternal alleles.
How does random fertilisation increase genetic diversity?
Any genetically unique sperm can fertilise any genetically unique egg, multiplying the variation generated by meiosis.
What is the Law of Segregation and how is it explained by meiosis?
The two alleles of a gene separate during gamete formation because homologous chromosomes separate during meiosis I.
What is the Law of Independent Assortment and when does it apply?
Alleles of genes on non‑homologous chromosomes assort independently during gamete formation.
Why do some traits not follow Mendelian phenotypic ratios?
Because dominance relationships between alleles are not always complete, or because genes interact.
What is complete dominance?
One allele completely masks the phenotypic effect of another in heterozygotes.
What is incomplete dominance?
The heterozygote shows an intermediate phenotype because neither allele is fully dominant.
How does incomplete dominance affect phenotypic ratios?
Phenotypic ratios mirror genotypic ratios because each genotype produces a distinct phenotype.
What is codominance?
Both alleles are fully and simultaneously expressed in the heterozygote.
What are multiple alleles?
A gene that exists in more than two allelic forms within a population.
Why is the ABO blood group a classic example of multiple alleles?
It involves three alleles that produce four possible phenotypes.
How do dominance relationships operate in the ABO system?
Two alleles are codominant with each other and both are dominant over the recessive allele.
What is pleiotropy?
A single gene affects multiple phenotypic traits, often seen in genetic disorders.
