Topic 8

• Autosomal chromosomes are all the others that are not sex chromosomes
• Autosomal linkage is when two or more genes are carried on the same chromosome. They will stay together through meiosis as long as theres no crossing over.
• Is genes are linked they will produce gametes AB and ab. 2 heterozygous organisms will produce offspring in the ratio 3:1 of dominant and recessive.
• if genes are not linked, the gametes produced will be AB, Ab, aB, and ab. 2 heterozygous will produce offspring in a ratio 9:3:3:1
• in a punnet diagram, you cross over the gametes of each individual. eg hetrozygous - AB and ab (AaBb)
• what is a type of discontinous variation?

  blood type and age
• what is a type of continuous variation?

  height and weight
• continuous variation is controlled by many genes (random assortment, crossing over), and the environment.
• what is etiolation?

  the lack of light
• what can etiolation cause?

  long weak stems

  smaller leaves

  pale yellow colour
• monohybrid inheritance evolves a single gene. eg AA or aa. A heterozygous of Aa will produce offspring ratio 3:1
• Dihybrid inheritance i two sets of genes. eg AABB or AaBb ect. This could be the colour and the shape of a plant.
• sex linkage is when a gene is located on the part of the X chromosome where there isn‘t a corresponding Y chromosome (as Y is shorter than X) in males.

  If a gene is there, it will always be expressed, even if its recessive, as there is no other gene on the Y.
• sex linked conditions include colour blindness and haemophilia. these conditions are more likely in male than female.
• directional selection is the movement to a favoured allele in a population
• stabilising selection is when there is a selection against the extremes, so there are more individuals in the middle
• diversifying selection is selecting for the extremes, against the most common
• genetic drift is the random change in allele frequency in a population due to chance. it is more common in smaller populations
• Steps in the hardy Weinberg equation

  • find frequency of recessive q*2
  • square root to find q
  • find p from p+q=1
  • use equation p*2 +2pq +q*2 = 1
• 5 reasons for significant difference between observed and expected values?

  mutations, gene linkage, epigenetics, random gamete fusion, crossing over
• the founder effect is when a small group of individuals leave a population and start a new one
• genetic bottle neck is the reduction in gene pool due to a a catastrophic event eg disease, hunting. It is unselective.