Characteristics and Inheritance

• Genetics


  Study of inherited characteristics called Traits
• Variations


  Different characteristics can have different variations (e.g. blond or brunette hair, blue or brown eyes)
• Alleles on homologous chromosomes


  Alleles are on the top of homologous chromosomes. One allele is inherited from each parent
• Mendel's most famous experiments involved breeding pea plants to study patterns of inheritance
• If a red-flowered pea was purebred, that means that all of its ancestors were red-flowered
• Homologous chromosomes

  You get one copy of each chromosome and therefore each gene from your mother and one from your father
• In Mendel's experiment with pea plants, the Second or F2 generation mostly had red flowers, but some had white flowers
• Characteristics

  Different genes code for different characteristics (e.g. hair colour or eye colour)
• Gregor Mendel was an Austrian Monk who carried out important experiments that formed the basis for genetics in the 1850s and 1860s
• Inheritance


  Passing of traits from parents to offsprings
• Alleles


  Variations of genes which code for each trait
• Mendel used pure-breeding peas which means that they all had the same traits
• Recessive characteristic


  Characteristic that remained hidden
• Allele for dominant trait is represented by an upper-case letter. E.g. R for red flower
• Each plant has 2 copies of a gene; one from its “mother” and one from its “father”
• Alleles


  The two variations of the flower colour gene
• Representing Alleles

  Alleles of a gene are represented using letters
• Genotype and Phenotype

  Genotype: actual genetic information carried by an individual; Phenotype: observable traits of the individual
• Each individual has 2 alleles for each trait (one from each parent)
• Homozygous vs Heterozygous

  Homozygous: An individual that has two of the same alleles on homologous chromosomes. Can be either both dominant or both recessive. Heterozygous: An individual that has two different alleles on homologous chromosomes
• Individuals have many genes on their chromosomes and can be heterozygous for one gene but homozygous for another gene
• Genotypes

  • RR: produce red flower
  • Rr: produce red flower
  • rr: produce white flower
• RR, Rr, rr represent the plant’s ‘Genotype’. Red or white colour of the flower is the plant’s ‘Phenotype’
• Why offspring have red flowers

  Because the allele for red flowers is dominant
• Alleles of a gene are represented using letters. The letter chosen is often the first letter of the dominant allele but it could also be the first letter of the recessive allele. However, both the dominant and recessive alleles will use the same letter
• Allele for recessive trait is represented by a lower-case of the same letter. E.g. r for white flower
• Dominant Characteristics 


  The most observable feature or trait. eg. Behaviour or apperance.