Extentions Of Mendelian Genetics Flashcards
Mendelssohn first law - law of segregation
Genes segregate at meiosis so that each gamete only contain one of the two posessed by the parent
Dyhybrid cross with two heterozygous phenotypic ratio
9:3:3:1
Mendels second law - independent assortment
Alleles of different genes assort independently during gamete formation
Off spring probablilty:
- probability of one parent supplying required allele times the probability of the other parent supplying it (add them together if both parents have both required allele)
- then times all probolbilties of the alleles of the phenotype
Two probability rules:
Product rule: independent events
Sum rule: mutually exclusive events (a or b)
Polymorphic :
One gene - many alleles
- each individual can only have two alleles, one on each homologous chromosomes
Incomplete dominance
- F1 has an intermediate phenotype (mix of both alleles) but suggests blending inheritance …
- F2 contains parental phenotypes thus rejects blending inheritance and supports particulate inheritance
Look at PowerPoint picture
Co-dominance
Where both phenotypes exist side by side within the organism - both parental phentoptypes are present in F!
Polygenic traits
- phenotype controlled by many genes that have an additive effect
- characters appear continuous of quantitative (non-discrete steps in range of phenotypes)
E.g skin colour, who’ll length, weight, IQ, milk yield, height - controlled by GROUPS of genes
Skin colour - additive effect
- coded by 3 genes, each of which has alleles coding for colour or no colour
- phenotype determined by total number of colour producing alleles - could be 0 - white to 6 - black
- ADDITIVE EFFECT
- the normal distribution typical of polygenic trait in a population in a bell curve
- the more genes involved, the higher number of phenotypic classes
Environment…
Affects phenotype
- environment smooths differences around phenotypes
LOOK AT POWER POINT PICS
