23. A dihybrid cross like the examples studied in lab with the corn plants (Tog
ID: 212778 • Letter: 2
Question
23. A dihybrid cross like the examples studied in lab with the corn plants (Tog X TtGg) should result in a: a. A 1:1 ratio of tall greens: dwarf albinos b. A 2:1 ratio of dwarf greens : tall albinos . 1 1 1 1 tall greens : dwarf greens : tall albinos: dwarf albinos d. A 9:3:3:1 tall greens : dwarf greens : tall albinos : dwarf albinos 24. You do a dual trait cross in fruit flies (you are watching two different trai ts). 50% of the offspring are new combinations not visible in the parents (are recombinants). The genes for these two traits: a. Are close together b. 5 map units apart c. Are on different chromosomes d. Either B or C could be true 25. A loci is the proper position of a gene on a chromosome a. True b. False 26. A researcher was doing her crosses in fruit flies and found that the hairy leg and dwarf antennae traits are almost always inherited together. These traits could be said to be: a. Homologous b. X-linked c. Y-linked d. Linked e. Recessive 27. One of the first ways genes were located on chromosomes is by constructing linkage maps. These maps are made by: a. Studying the recombination frequencies between two traits at once b. Staining a chromosome with fluorescent stains c. Studying a single trait through multiple crossesExplanation / Answer
23. Punnet square is depicted below:
TtGg
TG
Tg
tG
tg
TtGg
TG
TTGG
Tall green
TTGg
Tall green
TtGG
Tall green
TtGg
Tall green
Tg
TTGg
Tall green
TTgg
Tall albinos
TtGg
Tall green
Ttgg
Tall albinos
tG
TtGG
Tall green
TtGg
Tall green
ttGG
dwarf green
ttGg
dwarf green
tg
TtGg
Tall green
Ttgg
Tall albinos
ttGg
dwarf green
ttgg
Dwarf albinos
The ratio is 9 tall green: 3 dwarf green: 3 tall albinos: 1 dwarf albinos
Right option is d. 9:3:3:1
24. Recombination frequency is the number of recombinants produced in a genetic. As 50% recombinants were produced in the dual cross, recombination frequency is 50%. When genes are far apart from each other on same chromosome or when they are present on different chromosomes, they have recombination frequency of 50%. These genes are not linked and assort independently.
Recombination frequency of 1% is I map units. 5 map units (m.u) indicates a 5% recombination frequency.
Right option is c. are on different chromosomes.
25. Loci is fixed position of a gene or genetic marker on a chromosome. The locus of the OCA1 gene (Oculocutaneous Albinism Type 1) which is associated with albinism is 11q1.4-a2. Variants of genes are called allele.
Right option is True.
26. The genes for hairy leg and dwarf antennae are inherited together. Hence they are linked genes which are present on same chromosomes close to each other. These genes do not assort independently and are inherited together.
Right option is d. Linked.
27. Linkage maps are created by studying recombination frequency of two traits at once. If the recombination frequency (number of recombinant formed) is 50% the genes are linked and present close to each other on same chromosome. If the recombination frequency is below 50% the genes are not linked and preset either far apart on same chromosome or on different chromosome.
Recombination frequency= number of recombinant progeny/total number of progeny X 100%
Right option is a. Studying the recombination frequencies between two traits at once.
TtGg
TG
Tg
tG
tg
TtGg
TG
TTGG
Tall green
TTGg
Tall green
TtGG
Tall green
TtGg
Tall green
Tg
TTGg
Tall green
TTgg
Tall albinos
TtGg
Tall green
Ttgg
Tall albinos
tG
TtGG
Tall green
TtGg
Tall green
ttGG
dwarf green
ttGg
dwarf green
tg
TtGg
Tall green
Ttgg
Tall albinos
ttGg
dwarf green
ttgg
Dwarf albinos
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