Question

In: Biology

In cactus, long spines are dominant to short and pink flowers are dominant to white. A...

In cactus, long spines are dominant to short and pink flowers are dominant to white. A true-breeding short-spined cactus that is a carrier for flower color is crossed with a cactus that is heterozygous for both traits. This cross produces 200 seeds. How many of these seeds would you expect to germinate as short-spined, pink-flowered cacti?\

25 75 100 150

Solutions

Expert Solution

Lets consider,

Gene, control the traits for long spine is S and for pink flower is P.

  • possible dominant genotype for trait long spine would be SS(homozygous) and Ss (heterozygous) and recessive short spine genotype would be ss.
  • possible dominant genotype for pink flower would be PP (homozygpus) and Pp (heterozygous) and recessive genotype for white flower would be pp.

The genotype for true breeding short spined would be ss and genotype for carrier for flower color would be Pp (as it is carrier, genotype would be heterozygous). so, the genotype would be ssPp for parent one.

cactus for heterozygous for both the traits would be SsPp for second parent.

When cross occured,

ssPp x SsPp

possible genotype for parent one: sP and sp

possible genotype for parent two: SP, Sp, sP and sp

solving with punnett square:

SP Sp sP sp
sP SsPP SsPp ssPP ssPp
sp SsPp Sspp ssPp sspp

So, the frequency for short spined, pink flowered is: 3/8 = 37.5%

From the above result, we can expect that out of 200 seeds, 37.5 % that is equal to 75 seeds would germinate as short-spined, pink flowered cacti.


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