Complex Inheritance & Linkage Flashcards
(20 cards)
What determines traits in polygenic inheritance?
Traits are determined by multiple genes rather than a single locus
Each gene may partially contribute to the overall phenotype.
What are additive traits?
Traits where phenotypic effects are additive, such as skin colour
More pigment alleles result in a darker tone.
What is epistasis?
One gene masks the effect of another gene
Example: Albinism where the no pigment gene overrides hair/eye/skin colour genes.
How can epistasis explain complex traits?
Complex traits do not follow classic Mendelian ratios due to gene interactions
Epistasis illustrates this by showing how one gene can affect the expression of another.
What is the purpose of complementation testing?
To determine whether two recessive mutations affect the same gene or different genes.
What outcome indicates mutations fail to complement?
Same locus = offspring affected.
What outcome indicates mutations complement?
Different loci = offspring normal (carriers).
What is pleiotropy?
One gene affects multiple phenotypic traits
This violates Mendel’s idea that traits are independently inherited.
What is gene linkage?
Genes that are physically close on the same chromosome tend to be inherited together.
Who discovered gene linkage?
Thomas Hunt Morgan through studies on Drosophila.
What is crossing over?
Occurs during meiosis; breaks linkage if it happens between two linked genes.
What does crossing over lead to?
Recombinant gametes.
How is genetic distance measured?
In centiMorgans (cM).
What does 1 cM represent?
1% recombinant offspring.
How is the recombinant fraction (RF) calculated?
RF = (Total Number of Offspring / Number of Recombinant Offspring) × 100.
If there are 900 offspring parental types and 100 recombinants, what is the RF?
RF = 10% → 10 cM between genes a and b.
What is the setup for a two-point testcross involving gene a?
Gene a: a⁺ = long antennae (dominant), a = short.
What is the setup for gene b in a two-point testcross?
Gene b: b⁺ = green eyes (dominant), b = blue.
What does the outcome of a two-point testcross reveal?
Non-Mendelian ratios.
In a testcross with 900 parental-type offspring and 100 recombinants, what does RF indicate?
RF = 10% → genes are linked.
