H GBV Flashcards
what is the chi squared test explanation?
At 0.05 level of significance, calculated chi square value of _ is less/more than the critical value of . Probability is between and _. Differences between expected and observed results is not significant and is due to chance/is significant and is not due to chance.
Why is there a greater number than expected of the parental phenotypes?
The gene for _ and _ are LINKED/are on the same chromosome. eg Allele B and H tend to be inherited together and allele b and h tend to be inherited together, therefore parental gametes BH and bh occur at a higher frequency. When parental gametes fuse with bh in a test cross, this gives rise to more parental phenotypes.
If the two genes are unlinked, 4 different types of gametes will be found in equal numbers to form 4 different phenotypes in equal proportion.
How are recombinant gametes formed from test crosses?
Crossing over between non sister chromatids of homologous chromosomes may occur during prophase 1 of meiosis resulting in recombinant gametes (eg Bh). Crossing over result in the exchange of corresponding DNA segment of chromatids, thus separating alleles of linked genes and creating new allelic combinations of _ and _ in the chromatid. When crossing over occurs, the recombinant phenotypes will be produced in a test cross which occur less frequently than the parental phenotypes.
How are recombinant gametes formed?
During prophase 1 of meiosis, homologous chromosomes pair to form bivalents. Crossing over occurs between non-sister chromatids of HC resulting in chiasmata formation. The corresponding DNA segment from each non-sister chromatids of HC are broken, exchanged and rejoined. The exchange of genetic material between HC accounts for recombination of alleles of linked genes, giving rise to recombinant gametes which differ from parental arrangement of alleles.
How can different characteristics be inherited independently in dihybrid inheritance?
The inheritance of 2 characteristics is controlled by alleles of two genes found in separate chromosomes. During metaphase 1 of meiosis, pairs of HC align along the metaphase plate random to other bivalents, followed by the independent segregation of chromosomes to opposite poles of the cell. Different combinations of the alleles are formed in the gametes.
NOT CROSSING OVER!!!
suggest why _ alleles are dominant over _?
_ allele has the ability to manifest itself at the exclusion of the _ allele. in a heterozygote, the dominant allele if fully expressed in the phenotype. this is because _ codes for FUNCTIONAL proteins but _ do not code for functional proteins thus the effect of the recessive allele is masked in the phenotype of a heterozygote.
Locus definition
It is the specific position of a gene along the length of a chromosome. HC have the same gene at the same locus.
Allele definition
It is an alternative form of a gene which occurs as a pair of alleles at the same gene locus in DIPLOID cell. Different alleles of the same gene will have a unique nucleotide sequence.
what is the recombinant frequency equation? and what does mean?
If the expected phenotype ratio of 1:1:1:1 is seen, there is no linkage and the two genes are found on different chromosomes.
If not: no. of organisms showing recombinant phenotypes/total no. of offspring x 100% -> The further apart the two genes, the higher the possibility of crossing over occurring between the two genes, the higher the recombination frequency.
what gives rise to genetic variation?
Crossing over non-sister chromatids of HC during prophase of meiosis results in different allelic combinations. Independent assortment of HC at the metaphase plate during metaphase I of meiosis gives rise to different chromosome combinations in the gametes. Random fertilisation, which is the fusion of male and female gametes during sexual reproduction, gives rise to different combination of zygote.
