Term
| which genes does independant assortment take place? |
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Definition
| genes on different chromsomes - like homologous pairs at metaphase plate |
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Term
| crossing over takes part on which genes? |
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Definition
| genes on the same chromsome - like sister chromatids |
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Term
| what is a recombinant phenotype? |
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Definition
| where the combination of phenotypes differs from that found in either of the parents |
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Term
| name the 2 ways recombinant phenotypes can occur through |
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Definition
independant assortment (genes on different chromsomes)
crossing over (genes on same chromosme) |
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Term
recombination frequency is the % of progeny that inherit a combination of alleles that differs from either parent.
How do you work it out? |
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Definition
Recombination frequency =
number of recombinants/total number of progeny x 100%
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Term
| in fruit flies (drosophila melanogaster) how is the normal allele (wild-type) written? |
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Definition
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Term
| if 2 genes are very close together do they have a high or a low chance of crossing over? |
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Definition
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Term
| if gene A and B are further apart what are the chances of crossing over? |
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Definition
| the chnaces of crossing over are high and likely |
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Term
name one way the distance of genes on a chromosome is depicted..
what is the disadvantage of this method and name an alternate method |
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Definition
chromosme mapping.
disadvantage that it leads to underestimates of the distance between 2 loci due to multiple crossovers.
alternate method - the 3 point cross |
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Term
| when counting the number of progeny in a cross test what do the largest and the smallest numbers indicate? |
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Definition
largest numbers indicate parental types
smallest numbers suggest double cross overs |
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Term
| in a double heterozygote there are two possible arrangement of the alleles. what are they? |
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Definition
coupling heterozygote (b+ vg+) (b vg)
repulsion heterozygote (b vg+) (b+ vg) |
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Term
| there are six main factors that cause deviation from mendelian ratios. what are these? |
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Definition
| Sex-linkage, incomplete dominance, co-dominance, pleiotrophy, polygenic inheritance and epistatis |
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Term
| where was sex-linked inheritance first observed? |
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Definition
| drosophila fruit flies. where the Y chromosome lacks a gene and only requires one copy from the the female X chromosome to display a phenotype. |
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Term
| when a dominant allele does not completely mask out the effect of a recessive allele at the same locus this is known as? |
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Definition
incomplete dominance
eg. snapdragon flower. genes are RR=red and rr=white
but the F1 hybrid has an intermediate phenotype of pink |
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Term
| what happens to the ratio of the phenotypes in F2 when incomplete dominance is involved? |
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Definition
| the results show a modified 3:1 ratio...more like 1:2:1 |
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Term
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Definition
where each allele affects the phenotype in seperate, distuinguishable ways.
AB alleles in blood group are said to be co-dominant |
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Term
| whats the difference between incomplete dominance and co-dominance? |
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Definition
incomplete dominance - blending of traits..diluted phenotype
co-dominance - no blending: traits appear together and remain distinct in the heterozygote. eg. both A and B antigens on the RBC |
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Term
| where a single gene has multiple effects on phenotype it is said to be... |
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Definition
pleiotrophic.
eg. in a pea, the gene that determines flower colour also affects seed colour
eg. humans that are heterozygous for sickle cell are also resistant to malaria |
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Term
| where a single trait is determined by multiple genes is known as?.. |
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Definition
polygenic
eg, continous variation in the population, height, weight and skin pigmentation |
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Term
| when one gene masks or modifies the expression of another gene it is said to be.......... to that gene |
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Definition
epistatic
epistatis is greek for stoppage |
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Term
true or false.
if gene A is epistatic to gene B then gene A can mask the phenotype conferred by gene B? |
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Definition
this is true..we say gene A is epistatic to gene B
here B is known as the synthesis gene and A is known as the depostion gene |
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Term
| what is the epistatic gene also known as? |
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Definition
| the depostion gene...the one that it masks is called the synthesis gene |
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Term
| how does epistatis affect the outcome of a dihybrid cross? |
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Definition
| it modifies the 9:3:3:1 ratio to 9:3:4 |
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