Genetic inheritance

• All body cells except reproductive cells are called

  Somatic cells
• Somatic cells are diploid and divide by

  Mitosis to halve the chromosome number
• Who's the father of genetics?

  Gregor Mendel
• Genetics is

  The study of inheritance
• Inheritance/heredity

  Passing on of traits from one generation to the next
• Species

  Group of organisms that can interbreed and produce fertile offspring
• Traits

  • Physical/chemical characteristics that a living organism possesses
• Gamete

  Haploid sex cell capable of fusion
• Fertilisation

  Union of two haploid gametes to form a diploid zygote
• Gene

  Piece of DNA that contains instructions to make a protein
• Locus

  Position of a gene on a chromosome
• Alleles

  Different forms of a gene (e.g. eye colour: blue or green)
• Homozygous chromosomes

  Two alleles are the same
• Heterozygous chromosomes

  Two alleles are different
• Genotype

  Genetic make-up of an organism (e.g. BB, Bb or bb)
• Phenotype

  Physical make up of an organism, result of interaction of genotype with environment (e.g. BB = Brown eyes)
• Dominant

  Trait shown in the F1 generation, prevents working of recessive allele
• Recessive

  Gene does not work in the presence of a dominant allele
• Incomplete dominance

  Neither gene is dominant or recessive in the presence of a dominant allele (e.g. RR = red, rr = white, but Rr = pink)
• Progeny

  Offspring that is produced
• Mendel's 1st Law-Law of Segregation

  Traits are controlled by pairs of alleles. These alleles separate at gamete formation, with each gamete receiving one allele from each parent
• Mendel's 2nd law-The Law of Independent Assortment

  When gametes are formed, either pair of homologous chromosomes is equally likely to combine with either chromosome of a second homologous pair
• Incomplete dominance

  Neither allele is dominant or recessive with respect to each other.
• XX in humans: Female
• XY in humans: Male
• Linkage

  Both genes are present on the same chromosome
• Linkage leads to

  Less variation
• If genes are linked the ratio will be

  1:1
• If genes are not linked the ratio will be

  1:1:1:1 or 9:3:3:1
• Sex linked genes are

  Carried on the X or Y chromosome
• Sex linked traits are controlled by

  Genes on the X chromosome and are not present on the Y chromosome
• Example of sex linked condition

  Haemophilia
• Males are more likely to have a sex linked condition as there is no corresponding gene on the Y (shorter) chromosome→ Y-
• Why do recessive phenotypes show up more frequently in males? (More likely to express condition)

  They only need one recessive allele
• Non nuclear inheritance

  Inheritance of DNA via mitochondria and chloroplasts
• Non nuclear DNA is only inherited from the mother so does not follow


  Mendel's laws of genetics
• Disorders related to non nuclear inheritance

  Lack of ATP (energy) - effects muscular and nervous system