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Chapter 9 Mendelian Genetics and Chromosomal Basis of Inheritance

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  • What is heredity?

    Heredity is the transmission of traits from one generation to the next.

  • Who is considered the father of genetics and why?

    Gregor Mendel is the father of genetics for deducing fundamental principles of heredity by breeding garden peas in the 1860s.

  • Why were garden peas ideal for Mendel's experiments?

    Peas have short generation times, large offspring numbers, distinct varieties, and controlled matings due to enclosed reproductive organs.

  • Define 'character' and 'trait' in genetics.

    A character is a heritable feature (e.g., flower color), and a trait is a variant of that character (e.g., purple or white flowers).

  • What is a true-breeding variety?

    A true-breeding variety consistently produces the same trait over many generations of self-pollination.

  • What are the P, F1, and F2 generations in Mendel's experiments?

    P generation: true-breeding parents; F1 generation: hybrid offspring of P; F2 generation: offspring from self-fertilization of F1.

  • What did Mendel observe in the F1 and F2 generations when crossing purple and white flowered peas?

    F1 plants all had purple flowers; F2 showed a 3:1 ratio of purple to white flowers, indicating white was masked but not lost.

  • What are alleles?

    Alleles are alternative versions of a gene that account for variations in inherited characters.

  • Explain homozygous and heterozygous genotypes.

    Homozygous: two identical alleles (e.g., PP); heterozygous: two different alleles (e.g., Pp).

  • What is the law of segregation?

    Allele pairs separate during gamete formation, so each gamete carries only one allele for each character.

  • What is the phenotypic and genotypic ratio in Mendel's F2 monohybrid cross?

    Phenotypic ratio: 3 purple : 1 white; Genotypic ratio: 1 PP : 2 Pp : 1 pp.

  • What is the difference between phenotype and genotype?

    Phenotype is the observable trait; genotype is the genetic makeup (allele combination).

  • What are homologous chromosomes?

    Pairs of chromosomes carrying the same gene loci but possibly different alleles, one from each parent.

  • What is the physical basis of the law of segregation?

    Separation of homologous chromosomes during anaphase I of meiosis leads to segregation of alleles.

  • What is the law of independent assortment?

    Alleles of different genes assort independently during gamete formation, leading to genetic variation.

  • What phenotypic ratio results from a dihybrid cross with independent assortment?

    A 9:3:3:1 ratio of four phenotypes (e.g., round yellow, round green, wrinkled yellow, wrinkled green seeds).

  • How can a testcross determine an unknown genotype?

    Cross the individual with a homozygous recessive; offspring phenotypes reveal if the unknown is homozygous dominant or heterozygous.

  • What is the chromosome theory of inheritance?

    Genes are located on chromosomes, which undergo segregation and independent assortment during meiosis, explaining inheritance patterns.

  • What did Bateson and Punnett discover about linked genes?

    Some genes located close on the same chromosome tend to be inherited together, not following independent assortment.

  • What is crossing over and its genetic significance?

    Exchange of chromosome segments during meiosis producing recombinant gametes and new allele combinations.

  • How is recombination frequency used in genetics?

    It measures the percentage of recombinant offspring and helps map gene positions on chromosomes.

  • What is a genetic linkage map?

    An ordered list of gene loci on a chromosome based on recombination frequencies.