Inheritance Flashcards
Locus
Position of a gene on a particular DNA molecule
Co dominant
Both alleles are expressed
Polygenic inheritance
Many genes that control one characteristic
Recessive allele
Only expressed if both the organisms alleles are recessive
Dominant allele
The allele is always expressed
Allele
Different form of the same gene
Gene
Small section of DNA that coded for a specific protein
Homozygous
2 of the same alleles
Heterozygous
2 different alleles
Phenotype
How the gene is expressed and its interaction with the environment
Genotype
Genetic constitution of an organism (all the alleles an organism has)
What is the name for any change to a genotype
Mutation
Law of segregation (for monohybrid)
In diploid organisms, characteristics are determined by alleles that occur in pairs. Only one of each pair of alleles can be present in a single gamete.
Monohybrid inheritance
- Is a mating between two individuals in which the phenotype (character) is controlled by a single gene (one genetic locus) which has two or multiple alleles.
- test/cross to investigate he genotype of an unknown organism
Why are actual results of a genetic cross rarely the same as predicted?
- discrepancies are due to statistical errors
- the larger the sample the more likely the actual results come near to matching the theoretical ones
Dihybrid inheritance
A mating experiment between 2 organisms showing the results of 2 traits/genes
A hybrid organism is one that is heterozygous, meaning it carries 2 different alleles at a particular genetic position or locus
Get a 9:3:3:1 ratio
Law of independent assortment (for dihybrid)
Each pair of alleles for a particular gene can combine randomly with either of another pair of alleles from another, different gene
Co dominance explained
- both alleles expressed in the phenotype
- both equally dominant therefore both expressed
- when representing the alleles, they have a different capital letter which is written as a superscript on a letter that represents he gene
- F2 ratio is 1:2:1
Multiple alleles
Where there are more than two alleles of which only two may be present at the loci of an individuals homologous chromosomes
Sex linkage
Y chromosomes are shorter and so miss the sex linked allele that are on the long arm
Represent the crosses using the chromosomes letter and a superscript for alleles
Autosomal linkage
- the loci of 2 or more different genes are on the same chromosome
- the results DO NOT obey the law of segregation as they don’t segregate
- any two genes on the same chromosome are linked
- all genes on a single chromosome form a linkage group
- assuming no crossing over, all the linked genes remain together during meiosis and so pass into the gametes and offspring
- get a 3:1 ratio
- excluding the sex chromosome all the other 22 are called autosomes
Epistasis
When the allele of one gene affects or masks the expression of another in the phenotype
You get a 9:4:3 ratio not 9:3:3:1
What is the hardy Weinberg principle?
The proportion of dominant and recessive alleles in a population remains constant from one generation to the next.
What are the 5 conditions for the hardy Weinberg principle to be met?
- no mutations
- population isolated
- no selection
- large population
- mating within the population is random
What is the hardy Weinberg formula?
p2 + 2pq + q2
