An organism\'s genotype (AA, Aa, aa) is the combinarion of alleles present where

Question

An organism's genotype (AA, Aa, aa) is the combinarion of alleles present whereas the phenotype is the physical expression of the genotype. In the earlobe shape example above, an individual can have a genotype of AA, Aa or aa. People with AA or Aa genorypes have the unattached earlobe phenotype (Figure 7.6a), while those with an aa genotype express the attached earlobe form (Figure 7.6b). Note that dominant traits can be either homoygous (AA) or heterosygous (Aa) while recessive traits are always homosygous (aa) TASK 5-?PATTERNS OF INHERITANCE l: Simple Dominance Simple dominance is the term used to describe a common outcome of allelic combinations, where one allele, when a Information about alleles present in a parental population can be used to determine the probability of different geno- biallelic gene is in question, will dominate over the other and thus be expressed phenotypically typic and phenotypic ratios for a variety of traits in the offspring. In instances when only 1 or 2 traits are being considered the Punnett square (Figure 7.7) approach is used to facilitate the calculations to predict the possible outcomes of the parental cross. When only one trait (2 alleles) is being considered the cross is monohybrid while a dihybrid cross involves 2 traits (4 alleles). The Punnett square is a visual representation of the laws of probability that dictate the predictable outcomes of parental crosses. General instructions on how to perform a cross using the Punnett square approach Coi . Write down the genotypes of the parents I. 2. 3. 4. Note the gametes that each parent can contribute Draw a Punnett Square Across the top write the gametes that one parent contributes and along the side write the gametes contributed by the other parent Perform the cross 5. 6. Determine the genorypic and phenotypic ratios Figure 7.7 Example of a Monohybrid coss Since C-curly hair and C-straight hair, ¾ of the possible offspring will have curly hair while only ¼ will have straight hair Procedure In the example above (Figure 7.7), the genotypic ratio i 121 (1: OC, 2 C.I: cel while the phenotypic ratio is 31. You will now simulate a cross berween two heterotygous individuals, Tt and Tt. Each group should obtain two pennies. pennies simultaneously to represent the potential outcomes of a cross between two Tt individuals. A head s the dominant tall allele (T) while a tail symbolizes the recessive dwarf allele (t). Before you begin flipping the pen- nies, perform the Te x Tt cross in the Punnett square below to estimate the expected genotypic and phenotypic ratios 112

Explanation / Answer

Table for Figure 7.7 -

Here T is the dominant allele for Tall character and t is the recessive allele for Dwarf character.

Q32. We observed a rough ratio of 19:31:14. The ideal ratio should be 16:32:16 which is roughly the same.

Q33. The genotypic ratio was 19:31:14
And the phenotypic ratio was 50:14

Q34. No, Ratios are a constant characteristic in the laws of inheritance of characters when basic dominance is followed ie. No co-dominance, incomplete dominance or linkages are assumed. However if the coins are flipped 6400 times, it would only impart more accuracy to the values leading to constant ratios but would not change the ratios at all.

Q35 Albinism is inherited in an autosomal recessive manner. So a punett square just like in the above question can made. Here 'A' is dominant and 'a' is recessive.

The mother is a female with normal pigmentation but she had an Albino mother. So she is a carrier and her genotype would be Aa.
The father is an Albino male, so the genotype would be aa.

Upon making a punett square -

Genotypic ratio would be 2:2
Phenotypic ratio would be 2:2 - Two normal pigmented and two albino.

T t T TT Tt t Tt tt

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