In genetics, the dash symbol (–) is a "wild card" that stands for either the dominant allele or the recessive allele; for example, a– means the individual has either the genotype aa or aa. two genes that undergo independent assortment affect the shape of the seed capsule in the broadleaf weed known as shepherd's purse. each gene has two alleles, one of which is dominant for the shape of the seed capsule. genotypes of the form a– b–, a– bb, and aa b– have triangular seed capsules, whereas the seed capsules of aa bb genotypes are ovoid. what ratio of triangular : ovoid is expected from the cross aa bb x aa bb?

1/16 are ovoid

Explanation:

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From an AaBb genotype we can obtain four possible gametes AB, Ab, aB and ab.  With the Punnett square we can observe the crossing.  In the second Punnett square we can see the form A– B–

AB          Ab           aB          ab

ABAABBAABbAaBBAaBb

AbAABbAAbbAaBbAabb

aBAaBBAaBbaaBBaaBb

abAaBbAabbaaBbaabb

AB          Ab          aB          ab

ABA-B-  A-B-  A-B-  A-B-

AbA-B-  A-bbA-B-        A-bb

aBA-B-  A-B-  aaB-aaB-

abA-B-  A-bbaaB-aabb

The genotypes of the form A– B–, A– bb and aa B– have triangular seed capsules (15 of 16), while the seed capsules of the aa bb genotypes are ovoid (1 of 16).

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