Topic 3: Genes and the environment Flashcards
Give examples of phenotypes which are affected by genes and the environment
(5 examples)
- Human height
- Human skin colour
- Human hair colour
- Fur colour in Himalayan rabbits
- Cancer
What does height depend on in terms on genes? (1 point)
- Height depends on the combination of alleles inherited from both parents.
What are the environmental factors that promote height? (3 factors)
- More calcium for bone growth and protein for muscle growth in diet
- Warm climate/house – less energy used for heat production, so more energy for growth
- {Good health/lack of disease/antibiotics} – less energy used to fight disease, so more energy for growth
What are the environmental factors that limit/stunt height? (4 factors)
- Malnutrition – lack of calcium and protein in diet
- Cold {climate/house} – more energy used for heat production
- Disease – more energy used to fight disease
- Excessive exercise – uses up energy which could be used for growth
What is skin colour determined by
2 things
- many genes (polygenetic inheritance)
2. UV light (environment)
What is melanin? (1 point)
- dark protein pigment in skin and hair
How is melanin produced? (2 points)
- produced by melanocytes (melanin producing cells) from tyrosine (and amino acid) using the enzyme tyrosinase - the gene for tyrosinase must be switched on for melanin to be made.
- Melanin is packaged into vesicles called melanosomes.
What is melanin responsible for? (1 point)
- melanin is responsible for determining skin and hair colour and is present in the skin to varying degrees (depending on how much a population has been exposed to the sun historically)
Key Summary: What happens in the skin in high UV light to protect the DNA in skin from mutation (damage).
(6 steps)
- High UV light causes more MSH to be produced by brain
- more MSH receptors form on melanocytes
- more MSH binds to MSH receptors on melanocytes
- more melanin made (from tyrosine by tyrosinase enzyme)
- more melanosomes form and are transferred to skin cells
- more melanosomes collect around the nucleus to screen it from UV light to protect DNA from sun damage (skin darkens)
NOTE: They key word is “more” in step 1. For low UV-light, the process is the same but without the word “more”.
What is hair and fur colour determined by?
2 things
- genotype
2. UV light
Key Summary: Explain the effect of UV light on human hair colour
(5 steps)
- More melanin is produced by melanocytes in the hair follicle at the root of the hair
- Melanin is packaged into melanosomes and transferred to hair cells
- UV light causes chemical and physical changes to the melanin
- melanin is destroyed
- hair lightens
(seasonal fur colour change)
Summer:
- Foxes produce fewer ____ receptors
in summer/sunlight (opposite to in
human skin!)
- No melanin made in hair follicles
- _____ coat grows under _____
summer coat
Autumn:
- ______ summer coat moults in Autumn
(due to decreased daylength)
Winter:
- _____ coat remains
MSH
white
brown
brown
white
(Fur colour in rabbits and cats)
Parts of body at body temperature – warmer core of body:
- gene switched on and expressed,
so tyrosinase is made, but it is ______ - so NO melanin can be made
- _____ fur
inactive
white
(Fur colour in rabbits and cats)
Parts of body where temperatures are lower than body temperature/colder - extremities/ ears, nose paws:
- gene switched on and expressed,
so tyrosinase is made which is _____ - so melanin (dark pigment) is made
- ____ fur
active
dark/black
Key Summary: Explain how genotype and environment interact to produce fur colour in Himalayan rabbits
(3 steps)
- the phenotype of fur colour is the result of interaction between genotype and body temperature/temperature of the environment
- the gene/allele expression produces tyrosinase enzymes which are involved in producing fur colour by producing melanin
- Himalayan gene/allele – when this is switched on and expressed it produces tyrosinase enzymes which are inactive at higher temperatures, so white fur is produced on the warmer core of body only and black fur on cooler extremities eg. ears, nose
