Ch. 3 - Passing on Characteristics (Genetics)

• Reproduction


  The formation of new living things
• Asexual reproduction


  The formation of living things from one parent only
• Sexual reproduction


  The production of living things by combining cells from two parents
• Gamete


  Sex cell
• Sexual reproduction involves 2 gametes joining together to form a single cell called


  Zygote
• Fertilisation


  The joining or fusion of sex cells
• As a result of sexual reproduction, the offspring formed have features/characteristics of both parents. This means the offspring are not identical to the parents. This is the main benefit of sexual reproduction.
• The most common way animals reproduce is by sexual reproduction. Plants can reproduce sexually or asexually.
• Characteristics


  traits or features of an organism that can be passed on from parents to their offspring. Characteristics are controlled by genes (which are found on chromosomes).

  Genes are passed from parents to their offspring during reproduction.
• In asexual reproduction the parent passes exact copies of its genes to the offspring. This is why the offspring are genetically identical to the parent.

  For example, strawberries that reproduce by runners will taste, look and grow the same as the strawberries on the parent plant.

  In sexual reproduction the offspring have different genes.
• Humans have many genetically controlled characteristics.

  These include:

  • Eye colour
  • The presence or absence of freckles
  • Having two eyes
  • Having one heart
  • The ability to roll the tongue
• Plant characteristics controlled by genes include:


  • Colour of the fruit
  • Colour of the petals
  • Taste of the fruit
  • Height of the plants
• Humans have many characteristics in common. They have one heart, two eyes and the ability to produce chemicals such as saliva, sweat and hair.
• However, humans also have some differences (or variation). There are two types of variation:

  • Genetic (inherited)
  • Non-inherited (acquired)
• Genetic variation


  Differences passed on from parents to their children by genes. This means that genetic variation is inherited from the parents.

  For example, eye colour, the length of our eyelashes and the presence or absence of freckles are all inherited from our parents.
• Non-Inherited Variation


  Differences that are not controlled by genes. These variations do not pass from parents to their children. They have to be learned or practiced.

  For example, speaking a language, using a computer, reading or tying a lace are non-inherited variations.
• Chromosomes

  Thread-like structures found in the nucleus of each plant and animal cell. Most of the time, chromosomes cannot be seen in a nucleus because they are stretched out into extremely long, thin threads. Most human cells have 46 chromosomes.
• When cells divide, the chromosomes become shorter and thicker and can be seen using a microscope. At this time each chromosome looks like a tiny, thin thread. Chromosomes are made of a chemical called deoxyribonucleic acid (DNA) and protein.
• Genes

  short sections of DNA located on chromosomes. They control the production of inherited characteristics.
• Examples of Human Genes include:

  • The gene to make acid in our stomach
  • The gene to make the coloured chemical (pigment) in our eyes
• Patterns of Inheritance


  The inheritance of genetic characteristics often follows a pattern. This is because of the way in which genes may be inherited from each parent. The pattern of inheritance is best understood by following the outcomes of sample genetic crosses.
• Eye Colour in humans is controlled by a gene. The gene has 2 versions: 


  • The dominant version (represented as B) causes brown eyes
  • The non-dominant version, also called the recessive version, (represented as b) causes blue eyes
• B = brown eyes (dominant)

  b = blue eyes (recessive)

  • normally, the first letter of the dominant version is used
  • e.g. for brown eyes, B is used
  • The dominant version prevents the recessive version of the gene from working
• Genotype


  The genes an organism possesses
• Genotype

  Eye Colour

  
• Phenotype


  what the organism looks like

  for example, the eye colour is the phenotype
• Phenotype


  Eye Colour

  
• Genetic Crosses


  Examples

  
• Pedigree Chart

  A diagram showing the physical appearances of individuals in a family from one generation to the next.
• Example of a Pedigree Chart


  Pedigree Chart