LGS A-Level OCR Biology - Unit 6 - Patterns of Inheritance Part 2
This deck Epistatic alleles may produce repressor proteins or transcription factors that bind to the promoter of another gene, blocking transcription or enzyme function.
What may prevent linked genes from being inherited together
If they’re separated by chiasmata
Key Terms
What may prevent linked genes from being inherited together
If they’re separated by chiasmata
W/ crossing over in autosomal linkage
Genotypic and phenotypic ratios are variable
Parental types > cross-over type
Proportion depends on how often cross overs ocurred be...
Recombinant offspring
Offspring w/ a diff combination of alleles to either parent
Closer genes are located on a chromosome …
Less likely to be separated during crossing over –> fewer recombinant offspring
Recombination frequency
Measure of amont of crossing over occured in meoisis - indicating level of linkage
Also used to map genes loci ; 1% = distance of 1 map unit ...
Calculating recombinant frequency
No of recombinant offspring/ total no. of offspring
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| Term | Definition |
|---|---|
What may prevent linked genes from being inherited together | If they’re separated by chiasmata |
W/ crossing over in autosomal linkage | Genotypic and phenotypic ratios are variable Parental types > cross-over type Proportion depends on how often cross overs ocurred between two loci |
Recombinant offspring | Offspring w/ a diff combination of alleles to either parent |
Closer genes are located on a chromosome … | Less likely to be separated during crossing over –> fewer recombinant offspring |
Recombination frequency | Measure of amont of crossing over occured in meoisis - indicating level of linkage Also used to map genes loci ; 1% = distance of 1 map unit on chromosome |
Calculating recombinant frequency | No of recombinant offspring/ total no. of offspring |
50% recombination frequency | No linkage, separate chromosomes |
<50% recombination frequency | Gene linkage and IA has been hindered Signifies autosomal linkage Linked genes are inherited together Crossing over produces few recombinant offspring |
Homozygous | Has identical alleles on both chromosome |
H0 in chi squared | There is no sig. difference between expected and observed values |
Degrees of freedom in chi squared | No. of categories - 1 |
Epistasis | Interaction of genes at diff loci Genes masking the expression of other genes (not alleles) Gene regulaion is a example w. reg . genes controlling structural genes |
When can epistasis be seen | Multistep reactions |
Hypostatic | Gene affected by another gene | Cause the phenotype |
Epistatic gene | Gene that affects the expression of another gene; can happen as a result of dominant or recessive alleles |
Epistatic alleles | Another pair of alleles found at diff loci |
Antagonistic epistasis | Dominant and recessive epistasis |
Dominant epistasis | If there are ANY dominant alleles present in the epistatic alleles, masks expression of hypostatic alleles |
Phenotypic ratio in a heterozygous dihybid cross w/ dominant epistasis | 12:3:1 |
Recessive epistasis | Occurs when a pair of homozygous recessive alleles at one gene locus masks the expression of the hypostatic allele at a 2nd locus |