Inheritance🧬

• A gene is a unit of inheritance. It is a small segment of DNA that controls the production of one polypeptide that determines a characteristic
• Alleles are different form of the same gene
• Homozygous (RR/rr)

  heterozygous (Rr)
• Female XX, male XY
• Mutation is a sudden, random change in the structure of a gene or in the number of chromosomes in the nucleus.
• Gene mutation

  • albinism : people with albino allele (recessive) cannot produce a pigment for skin,hair and eye colour. They are sensitive to sunlight and easily sunburnt.
  • sickle cell anemia : gene controlling haemoglobin is affected. The mutated gene is recessive causing red blood cell to be sickle shaped which can interfere with the oxygen carrying property of red blood cells
• Chromosome mutations

  • Down syndrome : humans normally have 46 chromosomes. Down syndrome people have 47 (extra chromosome 21)
• Factors increasing rate of mutation

  • chemicals (eg: tar)
  • radiation ( eg: ultraviolet light, X-rays)
• What is a gene?

  A gene is a unit of inheritance that controls the production of one polypeptide determining a characteristic.
• Where is the gene for human eye colour located?

  On chromosome 15.
• What are alleles?

  Alleles are different forms of the same gene.
• What does the allele 'B' represent in the context of eye colour?

  The allele for black eye colour.
• What does the term 'phenotype' refer to?

  Phenotype refers to the expressed trait or observable characteristic of an organism.
• What is the genotype for Taylor Swift's eye colour?

  bb
• How is a genotype defined?

  A genotype is the genetic make-up of an organism represented by a pair of alleles.

  
• What does it mean if an organism is homozygous?

  It means the two alleles controlling the trait are identical.
• What does it mean if an organism is heterozygous?

  It means the two alleles controlling the trait are different.
• What is the difference between dominant and recessive alleles?

  A dominant allele expresses itself in both homozygous and heterozygous conditions, while a recessive allele expresses itself only in homozygous condition.
• What is the dominant allele for eye colour?

  Black allele (B)
• What is a Punnett Square used for?

  A Punnett Square is used to determine the genotype of the offspring.
• How many pairs of chromosomes do humans have?

  23 pairs

  
• What are the sex chromosomes in humans?

  Females have XX chromosomes, while males have XY chromosomes.

  
• Why might the observed ratio of boys to girls in a family differ from the expected ratio?

  Because the ratio figures are based on chance/probability and are often inaccurate with small sample sizes.
• What are variations in traits between individuals of the same species dependent on?

  Interactions between genes and the environment.
• What are the two categories of variation?

  • Continuous variation
  • Discontinuous variation
• What are the differences between discontinuous and continuous variation?

  Discontinuous variation:

  • Few clear-cut phenotypes
  • Controlled by one or a few genes
  • Not affected by environmental conditions
  • Examples: eye colour, blood group

  
  

  Continuous variation:

  • Range of phenotypes
  • Controlled by many genes
  • Affected by environmental conditions
  • Examples: height, skin colour
• What is mutation?

  Mutation is a sudden, random change in the structure of a gene or in the number of chromosomes.
• How can mutations produce variation between individuals?

  Mutations result in new alleles.
• What are examples of gene mutations?

  • Albinism: Recessive allele causing lack of pigment.
  • Sickle-cell anemia: Recessive mutation affecting haemoglobin.
• What is an example of a chromosome mutation?

  • Down's syndrome: Extra chromosome 21, resulting in 47 chromosomes.
• What is the typical rate of mutation?

  The rate of mutation is usually very low.
• What can increase the rate of mutation?

  The presence of mutagens such as chemicals and radiation.
• What are some factors that can increase the rate of mutation?

  • Chemicals (e.g., tar)
  • Radiation (e.g., ultraviolet light, X-rays)