Genetics 2: Mendels law Flashcards
How does the Chromosome theory of inheritance (behaviour of meiotic chromosomes) parallel Mendels laws
Mendel: At each loci there is a pair of alleles
Chromosome: Chromosomes come in pairs
Mendel: principle of segregation
Chromosome: chromosomes go to different pole during anaphase
Mendel: principle of Independent assortment
Chromosome: Independent ending up of chromosomes in a daughter cell
What are 2 Mendels laws
Principle of segregation: 1. Principle of segregation: During gamete production the two alleles segregate
so 1 gamete=1 allele and these fuse to restore diploid state
- Principle of Independent assortment: Each allele pair assorts its self independently of other allele pairs on different loci during gamete formation
What is the biochemical basis for complete dominance vs recessive. Compare to heterozygous
The dominant codes for a functional enzyme that makes the trait actively from basic precursor (ie chloride transport pattern)
Whereas the recessive is the one that has a mutation that doesn’t make a functional protein or enzyme therefore cannot actively make the trait. (defective).
A heterozygotes still has functional protein from dominant allele so OK
What is the Biochemical basis for incomplete/partial dominance in pink flowers
The dominant gene has the functional enzyme which is converting the colourless precursor to the colour.
In heterozygotes they have a functional and non functional enzyme so can’t convert all of the precursor so intermediate phenotype is produced = There is partial dominance of a trait
Compare the expression of a heterozygote phenotype for complete dominance, incomplete/partial dominance and codominance
Complete dominance : dominant trait
Incomplete dominance : blended phenotype
Co dominance : Full expression of both alleles
What is the basis for co-dominance (in heterozygotes)
Both alleles lead to two different proteins being produced.
Full expression of both alleles. eg. AB blood cell.
Define linked genes and what is special about them
Linked genes are genes located on the same chromosome and they tend to be inherited together.
Special: Linked genes don’t behave like mendelian inheritance. as they are not independently assorted.
Will there be recombinants if the genes are completely linked
No
How do you test for linked genes and what are the expected frequency of genotypes produced
You test cross the one expressing dominant phenotype by breeding with the recessive phenotype (homozygous recessive on both loci).
If independently assorted non recombinants and recombinants will be all 25%
If linked then the two non recombinant parent genotype will be more than 50% together (if there is some crossing over) or 50% each if there is complete linkage
How are recombinants generated for linked genes
Not by independent assortment but by crossing over which is a rarer event. Between only 1 pair of non sister chromatids in the middle where they line up. The closer the genes are together, the less likely crossing over is to occur between them
What is the relationship between distance between linked genes and frequency of recombinants and what is the maximum frequency of recombinant genotypes
Frequency of crossing over is proportional to distance between two genes- further apart any crossing over will cross them.
Recombinant frequency never more than 50% because half will always be the parental type (two non sisters on outside)
What does Recombination frequency=
number of offspring that are recombinants (both groups) / total number of offspring * 100
1% recombinant frequency = (units)
1 map unit or 1 centimorgan
How do you constructing a linkage map
By comparing the recombination frequencies between 2 genes you can see the proportion of distance between the two loci on the chromosome.
Ie. A–C—B
A and C compared and C and B and A and B and then these can be all added together like on a scale to see the distances between them
Why can expected recombinant frequencies not add up
Double crossing over can reduce the recombinant frequencies by turning it back to the parental type so that is why the sums of A–B can be smaller, so the other smaller parts don’t add together.
