Genetics And Inheritance- Paper 2 Flashcards
gene pool definition
All the alleles within an interbreeding population
Phenotype
Expression of its genetic constitution and its interaction within the environment
allele frequency
The number of times an allele occurs in a gene pool
Multiple alleles
More than 2 alleles for the same gene- produces a hierarchy of dominance
homozygous
Two copies of the same gene that are the same allele
Heterozygous
Two copies of the gene are different alleles
Dominant allele
Will always be expressed in the phenotype
Recessive allele
Only expressed in the phenotype if the genotype is homozygous
Codominant
Equally expressed within a phenotype
Mono hybrid ratio
3:1
Codominance ratio
1:2:1
Dihybrid ratio
9:3:3:1
Epsiatus ratio
Adds up to 16 but follows no specific ratio
Autosomal linkage ratio
If no crossing over: 3:1
9:3:3:1
Hardy Weinberg principle
The alleles frequency will remain constant from 1 generation to the next
Measures the allelic frequency
P + q= 1.0
P2 + 2Pq + q2= 1.0
What does HW predict and what are the conditions
The allelic frequency from one generation to the next will remind constant
No migration, mating is random, no gene mutations, no selection for particular gene
Should be a large population, should be random
Mono hybrid inheritance
Inheritance of a single gene which determines a single characteristic
Gametes are indicated by drawing a circle around allele
Fusion of gametes is random
Dominant characteristic rules for pedigree charts
Affected offspring must have at least one affected parent
Unaffected parents only have one unaffected offspring
If both parents are affected and have unaffected offspring , both parents must be heterozygous
Unaffected parents can face affected offspring if heterozygous.
sex linked
Controlled by a gene located on one of the sex chromosomes
A female needs two copies of a recessive allele for it to appear in the phenotype but a male only needs 1
Sex linked rules
If a daughter is affected her father is not, it is recessive and not sex linked
If a son is affected and mum is not and it is dominant, then not sex linked
Dihybrid inheritance
Two genes either can be on different chromosomes or linked on the same chromosome
Autosomal linkage
Non-sex linked genes - not directly involved in determining the sex, genes are on same chromosome
What increases the chance of independent segregation occurring?
The further the genes are apart- produces different variations on the chromosome.
What is the ratio for autosomal linkage if no crossing over occurs
3:1
All linked genes remain together and end up on the same gamete.
