Lecture 2 Flashcards
What four distinct processes contribute to genetic variation
- Mutation
- Independent assortment of chromosomes during meiosis I
- Crossing over between homologous chromosomes during meiosis I
- Random fertilisation of ova by sperm
What is a recombinant phenotype
a phenotype where the combination of phenotypes differs from that found in either of the parents
Which two processes can recombinant phenotypes occur through
idenpendent assortment and crossing over
What is crossing over
-the process of genetic recombination that gives rise to new combinantions of linked genes
-occurs during phachytene phase of prophase I
-begins with synapsis (pairing of homologous chromosomes
-formation of synaptonemal complex leads to crossing over between homologous chromosomes
What is a synaptonemal complex
A protein zipper that holds homologous chromosomes together in the tetrad
Equaion for recombination frequency
(no. of recombinants) / (total no. of progeny X 100%
What is recombinantion frequency
the percentage of the progeny that inherit a combination of alleles that differs from either parentt
how are recombination frequencies estimated
use of a testcross (cross between double or triple heterozygote anad a double recessive line eg Aa Bb x aa bb)
Who was first to observe gene linkage
T.H.Morgan
6 deviations from Mendelian ratios
- Sex linkage
- Incomplete dominance
- co-dominance
- pleiotropy
- polygenic inheritance
- epistasis
what is incomplete dominance
where a dominant allele does not completely mask the effect of a recessive allele at the same locus
what is co-dominance
where each allele affects the phenotype in separate distinguishable ways
what is pleiotropy
where a single gene has mulitple effects in the phenotype
what is polygenic inheritance
when a single trait is determined by multiple genes
what is epistasis
when one gene masks or modifies the expression of another gene, it is said to be epistatic to that gene
