Inheritance and variation

Sexual reproduction

%%Sexual reproduction:%% involves two parents where the male and the female gametes join together to form a zygote

  • In sexual reproduction genetic information from two different individuals combines together during fertilisation to produce offspring
  • The offspring will be very like the parents but they will have very different characteristics that differ from both

Asexual reproduction

%%Asexual reproduction%%: involves one parent with the offspring having identical genetic information to the parent

Examples of sexual respiration in plants

%%Strawberries%%: runners

%%Onions%%: bulbs

%%Potatoes%%: tubers

Other examples of asexual reproduction in other organisms

Asexual reproduction occurs in one-celled organisms called amoeba

Variation

%%Variation%%: the way members of the same species differ

  • Changes in DNA are responsible for variation
  • These changes are called mutations

%%Species%%: a group of organisms that can breed with each other and produce fertile offspring

%%Fertile%%: when an organism can produce young

DNA

%%DNA%%: DeoxyriboNucleic Acid

  • Double helix shape
  • Sides made up of sugar and phosphates
  • The steps are made up of four different substances called bases

The four bases are

  • Adenine: A
  • Thymine: T
  • Guanine: G
  • Cytosine: C

Chromosomes

%%Chromosomes%%: lengths of DNA wrapped around protein

  • Each species has a particular number of chromosomes in their cells
  • Humans have 46 chromosomes in each cell
    • 23 from mother => egg
    • 23 from father => sperm
  • each human cell has about 2 m of DNA in it’s nucleus
  • DNA is super coiled

Genes

Genes: lengths of DNA along a chromosome, each gene controls the making if a particular reason

  • Only 3% of DNA forms genes
  • 97% => junk DNA => does not code for anything
  • 25,000 genes on their 23 their chromosomes => each chromosome has 1,000 genes on average
  • Each chromosomes from a mother has a corresponding chromosomes from their father
  • Environment can also effect gene

Where are the pairs of gene controlling a particular trait located?

  • Each gene on a chromosome has a corresponding gene controlling gene the same trait on the same place on its partner chromosomes

Mendelian inheritance

Inheritance

Inheritance: the way traits are passed from parent to offspring

Who was Gregor Mendel

  • Born in Austria
  • Augustinian monk who thought natural science
  • He researched inheritance and variation

What did he discover?

  • Cells of an organism carry two genes for the control of each trait
  • Gametes carry one gene from each trait
  • When gametes fuse during fertilisation the genes are in pairs again in the zygote
  • When an individual develops from the zygote all the cells in the body have two factors controlling each trait

Non-inherited and inherited traits in humans

  • Non inherited traits
    • ability to cycle
    • play football
    • speak a foreign language
  • Inherited traits
    • blood type
    • eye colour
    • hair colour
    • ear lobes
    • widow’s peak

Mendelian crosses

  • %%Expressed%%: when the protein a gene is controlling is actually made
  • %%Genotype%%: the genes that an organism possesses
  • %%Phenotype%%: the trait that can be seen in an organism
  • %%Genotype%% + environment = Phenotype
  • %%Dominant%%: a gene that prevents another gene from working
  • %%Recessive%%: a gene that is prevented from working

Denoting crosses

  • Letters are used in genetic crossed to denote genes
  • Dominant => capital letters
  • Recessive => small letters