Monohybrid and Dihybrid Inheritance Flashcards
Define gene
A section of DNA which codes for a protein
Define genotype
All the genes of an organism
Define phenotype
Observable features of the genotype and environmental influences
Define allele
A different form/variation of a gene
Define homologous chromosome
Chromosomes which contain the same genes at the same loci
Define heterozygous
When alleles of each chromosome are the same
Define homozygous
When alleles of each chromosome are different
Define dominant
An allele that expresses itself even if present with the recessive allele
Define recessive
An allele that only expresses itself only in the presence of an identical allele
Define monohybrid
Monohybrid means inheritance of a single characteristic (controlled by one gene)
What did Mendel do?
Started all his experiments with pure breeding parents and coined the phrases ‘dominant and recessive’
Process of monohybrid inheritance (with ‘height in pea plants’ example)
- Define alleles = T for tall plant (dominant)
t for dwarf plant (recessive) - Define parental phenotypes = pure breeding tall x pure breeding dwarf
- Define parental genotypes = TT x tt
- Define games = T T x t t
- Find F1 genotypes by doing cross with a punnet square (results = Tt Tt Tt Tt)
- Define F1 phenotypes = All heterozygous so ALL TALL
2 pea plants. 1 is pure breeding for greed pods. 1 is pure breeding for yellow pods. The green pod is dominant to yellow. After breeding the pod for TWO generations, how many of 580 plants will have green and how many will have yellow?
Monohybrid inheritance x2
FIRST GENERATION
Alleles:
Dominant = G = green
Recessive = g = yellow
Parental phenotypes = pure breeding green x pure breeding yellow
Parental genotypes = GG x gg
Gametes = G G x g g
F1 genotypes (after doing punnet square) = Gg Gg Gg Gg
F1 phenotypes = All heterozygous = ALL GREEN (after 1st generation)
2ND GENERATION
F1 phenotypes = green x green
F2 genotypes = Gg x Gg
F2 gametes = G g x G g
F2 genotype (after doing punnet square) = Gg Gg Gg gg
F2 phenotype = 3 green 1 yellow
3/4 x 580=435 green 1/4 x 580=145 yellow
What does F1 stand for
1st generation
Define dihybrid
Dihybrid looks at the inheritance of 2 genes at the same time
What is autosomal linkage
Where the genes looked at in dihybrid inheritance can be on different chromosomes or on the same chromosome
Process of dihybrid inheritance (example of pea plants seed shape and seed colour)
- Define alleles
Shape = Round = R (dominant)
= Wrinkled = r (recessive)
Colour = Green = G (dominant)
= Yellow = g (recessive) - Define parental phenotypes = pure breeding round and green x pure breeding wrinkled and yellow
- Define parental genotypes = RRGG x rrgg
- Define gametes = RG RG RG RG x rg rg rg rg
- Find F1 genotypes (using punnet square) = RrGg
- Define F1 phenotypes = All heterozygous round and green
What is the ratio if both genes are heterozygous for a dihybrid cross
9:3:3:1 ratio always
Why may you not always get a 9:3:3:1 ratio in real life with heterozygous parents
Because fertilisation is random, you would only see these proportions in a big population
What is the equation for the chi-squared test
Χ² = Σ [ (O– E)² / E ]
