Inheritance Flashcards
What is the meaning of allele
it is an alternative form of a gene
It codes for different forms of a gene product.
Alleles occupy the same gene loci on homologous chromosomes
It can be dominant recessive or codominant
What is a locus
It is a specific location of a gene along the chromosome
Can be occupied by different alleles of the same gene.
Suggest how test cross can help map position of genes on the chromosome
1.recombinant frequencies can be calculated by using no. of recombinant phenotypes/no. of phenotypes x100% of different pairs of genes
2.value of map units can reflect the distance between 2 genes along the chromosome
- If expected ration of 1:1:1:1 is obtained after test cross, the two genes are located on different chromosomes.
Why is it useful to carry out chi-squared test on the results (test cross)
1.to determine if deviation between expected numbers and observed numbers are significant
And to determine of deviation is due to change or not.
2. If p<0.05 the deviation is significant and if p>0.05 the deviation is not significant.
and observed ratio will not be 1:1:1:1 or will be 1:1:1:1.
Why is there a small number of mutant phenotypes in the wild
1.Mutants are disadvantaged in the wild, they are unable to fly long distances to find food.
They will not be able to survive to reproduce and pass down mutant alleles to offspring
2.mutations are coded for by recessive alleles. Recessive phenotype will be masked by dominant allele.
What is the conclusion u can draw form the probability of results p>0.10
At p=0.05 , degree of freedom 2 ,the calculated x^2 value is smaller than the critical x^2 value.
The deviation between observed and expected results are not statistically significant .The deviation is due to chance alone.
- Do not reject Ho (no statistically deviation)
Expected phenotypic ratio of 2 () :():() follows
Suggest a mechanism by which A^s suppress yellow pigment production.
- A^s allele codes for an active enzyme that degraded yellow pigment. 1 allele of A^s results in the production of enzyme that degraded yellow pigment resulting in the ‘eyeless’ phenotype.
- The A^s allele codes for a high affinity inhibitor. The presence of one allele results in the production of the high affinity inhibitor which binds to the active site of the enzyme that produces the yellow pigment with high affinity, preventing the colourless precursor substrate from binding to the active site. This results in the ‘eyeless’ phenotype.
3.The A^R allele codes for a less active enzyme which degraded less yellow pigment./ results in the production of an inhibitor with low affinity. It will bind to the active site of the enzyme less efficiently producing the yellow pigment so that some of the colour precursor substrate can still bind to the active site producing a small amt of yellow pigment.
Explain why there is a range of phenotypes
This is due to polygenic inheritance. The phenotype is controlled by many genes.
Overall phenotype is due to the additive effect of many genes.
Each genes has a small impact on the overall phenotype.
The phenotype can be influenced by environmental conditions.
Suggest why range of variation is greater in the second generation than in the first generation.
The parental generation is pure-breeding homozygous while the F1 generation is heterozygous. Thus there is the same genotype and very little variation among the F1 generation.
Crossing over between non-sister chromatids of homologous chromosomes to form chiasmata and recombinant chromosomes.
Independent assortment and segregation of alleles during metaphase and anaphase.
Gives rise of different alleles in gametes.
Random fertilisation of F1 gametes leads to greater variation in F2
Variation could also be because of multiple alleles( 3 or more alleles at the same gene loci) controlling the phenotype.
Suggest a molecular basis for the gene interaction described
S/s R/r gene loci codes for enzymes governing the same metabolic pathway
S allele codes for the functional enzyme which produces the pigment precursor molecule which acts as a substrate for the enzyme codes for by the R allele to produce red pigment and a substrate for the enzyme coded for by the r allele producing the yellow pigment.
The allele s codes for a non functional enzyme resulting in no pigment precursor molecule produced. Hence there is no pigment in the homozygous recessive onion with as genotype regardless of the alleles found in the R/r gene locus
