Inheritance,genes & Chromosomes Flashcards
What are the 2 theories emerged to explain breeding experiments ?
Blending inheritance -gametes contain hereditary determinants that Blending in the zygote.offspring phenotypes are intermediate
Particular inheritance-hereditary determinants are distinct and remain intact at fertilization
What is Mendel’s monohybrid experiment ?
When 2 strains of peas with contrasting traits are bred their characteristics are irreversibly blended in succeeding generations
Plant true breeding round seed and true breeding wrinkled seed
no blending- F1 -1 dom trait present
2 filial generation both dom & rec traits present in ratio of 3:1
Hypothesis is rejected -no irreversible blend of characteristics & rec trait can reappear in succeeding generation
Inheritance genes follows Mendelian law
Mendel proposed that hereditary determinants occur in pairs & segregated from one another during formation of gametes
Parental generation (P) = ♂ RR x ♀ rr
Gametes R R. r r
Each pea plant offspring would inherit one of its pair of heredity determinants from each parent
What is an allele ?
When gene has different forms causing different traits
Different version of the same gene
Define homozygous ?
Organism which has a gene for 2 alleles that are the same
Define heterozygous ?
Organism that has genes which have 2 different allele
One may be dominant over the other the presence of a recessive allele explains how a trait could reappear in the next generation
Define Phenotype ?
Is the physical appearance of an organism
Define Genotype ?
Is the genetic constitution of an organism
What did Mendel propose ?
That the phenotype is the result of the genotype
Only when you have 2 recessive alleles will you see the recessive phenotype
MENDELS FIRST LAW ?
The law of segregation:
The 2 copies of a gene separates during gamete formation ;each gamete receives only one copy
Mendels 2nd law ?
Independent assortment : copies of different genes assort independently
Define codominance
2 alleles produce phenotypes that are both present in heterozygote
How blood group system ?
The ABO blood group system results from an enzyme that adds specific groups to oligosaccharides in red blood surface
IA &IB alleles prod diff versions of the enzyme
IO allele prod neither
Define Epistasis ?
Phenotypic expression of 1 gene is influenced by another gene
Coat colour in Labrador retrievers is determined by the colour gene B:
But for alleles B (black) and b (brown) to be expressed, allele E of a separate gene (pigment deposition) must also be expressed.
An ee dog is yellow regardless of which B alleles are present. Gene E is said to be epistatic to gene B.
What affects phenotype ?
Environment
Eg) point restriction in Siamese cats and rabbits an enzyme that produces dark fur is inactive at higher temp s most fur is white even though allele to prod enzyme is present
Expressivity: degree to which genotype is expressed in an individual
