6.1.2 (a)

Question 1

In animals what are the environmental factors contributing to phenotypic variation?

Answer 1

• Poor diet management in animals can lead to a change in body size and mass – leading to either obesity or being severely underweight
  
  • A lack of exercise can also lead to obesity – leads to health problems (e.g. stress on vital systems and major organs)
• Language & dialect spoken
• Scarring/limb loss

Question 2

In plants, what are the environmental factors contributing to phenotypic variation?

Answer 2

Chloriosis and Etiolation​

Question 3

What is chloriosis and what are its causes?

Answer 3

• Chlorosis – leaves look pale/yellow due to lack of chlorophyll production;
• they have normal genes to produce chlorophyll, but environmental factors affect physiology of the plant but cause the same phenotypic change.

Causes:

Lack of light: if a plant/grass is covered by something, there is no light, chlorophyll production will stop to conserve resources that would be used for photosynthesis

Mineral deficiencies: If a plant lacks iron or magnesium, they act as cofactors stopping the enzyme used to manufacture chlorophyll – leaves turn yellow

Viral infection: viruses interfere with cell metabolism, which stops tissue from synthesising chlorophyll

Question 4

What is etiolation?

Answer 4

Etiolation – where plants grow in the absence of light

• Characterised by plants with long, weak stems due to lack of internodes
• Etiolation increases the likelihood of a plant reaching light to photosynthesise
• Apical dominance and gibberellins stimulate the longitudinal growth

Question 5

What genetic factos contribute to phenotypic variation?

Answer 5

• Genetics can be a risk factor in obesity
  
  • Mutations in chromosomes can cause the deposition of fat to be altered
  • In humans, we stop eating when dopamine levels reach a threshold (monitored by dopamine receptors)
    
    • Some people have an allele with fewer dopamine receptors – they overeat

A phenotype can be polygenic (characterised by multiple genes) or monogenic (characterised by a single gene)

Question 6

How can genetic variation rise from meiosis?

Define:

Allele

Genotype

Phenotype

Answer 6

In meiosis

• Crossing over to produce recombinant chromatids during meiosis gives a new combination of alleles (still same genes)
• The orientation of bivalents in metaphase I will produce a random combination of maternal and paternal chromosomes in the gametes (independent assortment of homologous chromosomes)
• In metaphase II, the independent assortment of the sister chromatids also gives a random combination of alleles

Allele: A variant of a gene

Genotype: The combination of alleles an organism has (genetic makeup of an organism)

Phenotype: Observable characteristics of an organism

Question 7

How does genetic variation rise from sexual reproduction?

Answer 7

In Fertilisation

• The combination of alleles in any given sperm or egg is random, and the fusing of any given sperm or egg is random, so the potential for genetic variation is high