8.1 Genetic information


Origins of genetic variation

-Meiosis as a source of genetic variation -->

  • independent (random) assortment= the components of the chromosome pairs are distributed randomly , so any number from 0 to 23 chromosomes in your gametes can come from the paternal or maternal chromosomes
  • crossing over (recombination)= during meiosis, large multi-enzyme complexes cut and join bits of the maternal and paternal chromatids together at the chiasmata, this exchange of genetic material leads to increased genetic variation

-there are three types of mutation --> 

  • point/gene mutations= miscopying of one/a small number of nucleotides. Inc substitution, deletions, insertions etc
  • chromosomal mutaions= changes in the positions of genes w/in the chromosomes. More likely to show a measurable change in the organism
  • chromosome mutations= when an entire chromosome is lost during meiosis or dupliacted in one of the cells due to an error

-random fertilisation as a source of mutation -->

  • when the gametes of 2 unrelated individuals fuse, this creates genetic variation
  • the combination of female and male gametes is random

-the physical and chemical characteristics that make up an organism are known as the phentoype

-the genotype is the genetic information

-the phenotype is partly the result of the genotype and partly the result of an organism's environment

-each gene on a chromosome is a different segment of DNA, coding for a particular protein or polypeptide

-the chromosomes in a homologous pair carry the same genes, except for the sex chromosomes

-the gene for a particular characterisitic is always found in the same position (locus)

-each gene exists in slightly different versions, called alleles

-if both alleles for a particular characteristic are identical then the individual for is homozygous for that characteristic

-if the two alleles for a particular characteristic are different, then the individual is heterozygous for that characterisitic

-polygenic= traits determined by several interacting genes

-homozygotes are referred to as true breeding as becuase if you cross two homozygotes for breeding,all of the resulting offspring will b ehomozygous for that trait

-when one gene at a time is considered in a genetic cross, it is called a monogenic cross

-the first generation on a mongenic cross (punnet square) is called F1 (fillial one)

-a test cross is sometime used to reveal the parental genotype


  • discovered the ratio for when looking @ more than one gene at a time
  • 9:3:3:1
  • law of segregation= one allele for each trait is inherited from each parent, giving a total of two alleles for each trait. The segregation in each allele takes place when the gametes are formed
  • law of independent assortment= different traits are inherited independently of each other
  • some traits havr multiple alleles --> there are more that 2 possible…


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