Cell Differentiation Flashcards
Define cell differentiation
The process by which a less specialized cell becomes more specialised for a particular function
Define locus
Place on a chromosome where any particular gene is found
Digenic (dihybrid) inheritance
The inheritance of two pairs of contrasting charcteristics at the same time
If the results of dihybrid inheritance is not what expected , what might be the cause
Small sample size
Experimental error
Random event -
Unexpected ratiocan mean the genes being examined are both on the same chromosome (they are linked)
Experiment that illustarted by some environemtn
- cloned plants grow diffrently when exposed to to varing amount of light
- food available affects the ability of niamls to acheive their full potential in terms of growth
Example siamese cats
-genotype suggest that they should have a dark fur all over their body ( due to melanin produced in the process involving tyrosinase enzyme)
How ever a mutaiton occuring in the gene of siamese cat results in inactivation of tyrosinase enzyme at normal temperature
—> light coat since tyrosinase inactivated at body temperature
The dark fur is a result of melanin
Melanin is produced using an enzyme called tyrosinase
These animal contain a mutated form of tyrosine which becomes inactive at normla body temperture and is only function at lower temperature
Therefore the animal are mostly pale but the extremities where thr temperature is cooler the enzyme is not denatured and the fur is black
Interaction between genes the environment
Characteristics/traits influenced by both genetic factor and environment factors
Continuous variation
Phenotypic features which show a range of values
- usually polygenic
- usually affected by both genetic and environmental factors
Discontinuous variation
Phenotypic features which are present or not
- usually inherited by one or small number of genes
- usually affected by genetic factors
A patch of white fur is removed firm the back of a rabbit which has a chocolate point pattern to its fur. A cool pack is keptt on the area of the skin as the fur grwos back. The new fur which grows is dark
The rabbit have a gene for an enzyme that produce darker colour hair
The rabbit has a mutation that means the enzyme which prodces the dark colour is inactive at normal temperature. When the fur is removed and a cool pack in place the temperture in that area is lowered . So, the enzyme remains active and melanin pigment is produced. The skin is cooloer and lose heat easily
When fur is removed there is enough of a drop in temperture to allow the enzyme to work, so dark pigment is produced and the fur is dark. However, once the dark fur has grown the skin is ekpy warm so at the next mounlt as new fur grows, the enzyme is inactive as the skin is at normla body temperture under fur- so new fur is cream again
If a siamese cats need surgery an area of fur will be shaved off the body the body ti leave a patch of bare skin. The fur that grows back over this skin is dark. It is not until after the next moult that the fur returns to tis normla cream colour
A mutation in siamese cats result in a version of tyrosine that is inactive at normal body temperture and onyl works at lower temperture. After surgery, the shaved area of the skin will be cooler than normla so the enzyme is not denatured and as a result the fur that regrows undere the insulating layer of existing dark fur, so the skin is warmer, the tyrosine is inactive and the fur grows pale.
Why are data frin identical twins reared apart even more useful than data from twin brought up togther
Identical teins reared togther have the same genes and simialr environement. This allows scientist to see how closely they are the same and can compare pairs of identical twins in different environemnt. Hwoever twins rearedd apart have the same genes but different environemnt , so looking at similaries and difference gives an clearer picture of hoe strongly phenotypic characteristic are affected by genes and by environement
Explain why characteristic affected by both genotype and environemnt espcially polygenic characteris show continuous variation
Because there are multiple combination of diffeent genes interacting with almost infinite variation in an environsment, which means there will be huge amount of variation across a population for those characteristics and no two ( or more) simple forms will be found
Siamese cat and
Genotype suggest that they should have a dark fur all over their body (due to melanin produced in the process involving tyrosine enzyme )
However, a mutation occurring in the gene of Siamese cat result inactivation of tyrosinase enzyme at normal temperature
—> light coat since tyrosinase inactivated at body temperatures
Summary of Siamese cats
At normal body temperature , the enzyme tyrosinase is inactivated therefore the fur is pale in body colour
Except the temperature is lower the enzyme is not denatured as a result the fur is dark
—> dark extremities
