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Applied Biology - Week 4 Lecture 2 (Inheritance patterns (Non-Medelian…
Applied Biology - Week 4 Lecture 2
Scientific approach to identify the laws of inheritance
Mendel discovered basic principles by using peas
TECHNIQUE:(flowers) Removed the stamen, transferred pollen from white flower to egg bearing carpet of purple flower. He then planted the seeds and the first offspring was purple flowers
Two distinct forms
True-breeding
Conclusions from pea and flower experiments
From his experiments he related a dominant trait and a recessive trait
What he called a "heritable factor" is what we now call a gene
Concept 1: Alternative versions of a gene account for variations in inherited characters = Alleles
Concept 2: For each characteristic, an organism inherits two alleles, one from each plant. Two alleles may be identical (true-breeding) or they may differ (diploid)
Concept 3: Dominant allele determines organisms appearance and the recessive allele has no noticeable effect
Concept 4: Two alleles separate during gamete formation THUS an egg of a sperm gets only one of the two alleles that are present in the parent organism
Punett Square
Capital letter = dominant allelle
Lowercase = recessive allele
Homozygous = two identical alleles
Heterozygous = Two different alleles
E.G. PP and Pp have the same phenotype (purple) but different genotypes
Test cross: is used to determine homozygous dominant or heterozygous
Breed with homozygous
If any
Phenotype - appearance
Genotype =
Law of independent assortment
Each pair of alleles segregates independently to the others
Only applies to genes on different chromosomes or those far apart on the same chromosomes
Probability Laws govern Mendelian inheritance
Alleles of one gene segregate into gametes independently of another genes alleles
Inheritance patterns
Many heritable characters are not determined by only on gene with two alleles
Non-Medelian inheritance
Degree of dominance
Complete dominance
Pheontype of heterozygote are identical
Incomplete dominance
Hybrid Phenotype somewhere inbetween the phenotype of the two parents
Codominace
two dominant alleles affect the phenotype in separate, distinguishable ways
Multiple Alleles
Blood types
Multiple Phenotype
Pleiotrophy = one gene influences multiple, seemingly unrelated phenotypic traits
These alleles are responsible for the multiple symptoms of certain hereditary diseases
Two or more genes
Many traits are determined by two of more genes
Epistasis = one gene alters the phenotypic expression of another gene
Environmental impact on Phenotype
Phenotype can depend on environment as well as genotype
Mutlifactorial = genetic and environmental factors collectively influence phenotype
Hydrangea flowers of the same genotype range from blue to pink = depending on soil acidity
Human Traits
Humans are not good subjects for genetic research
Generation time is too long
Parents reproduce relatively few offsrping
Breeding experiments are unacceptable
Behaviour of Recessive alleles
Recessive inherited disorders
Only exhibited on homozygous for the allele
If a recessive allele is rare, the the chance of the two carriers meeting ans mating is low
Dominant inherited disorders
Dominant alleles that cause a lethal disease are rare and arise by mutation
Mutlifactorial Disorders