(15 points) One of the accepted scientific theories describing the origin of life on Earth is known as chemical evolution. Accor
ding to this theory, which of the following events would need to occur first for life to evolve?
2 answers:
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Answer/Explanation:
- <em>See attached images showing the crosses on a Punnett square as well as the genotype and phenotypes of each cross.</em>
I. Cross between a female Gg with a male gg (GG X gg):
1. Probability of getting gray offspring (Gg) = 2/4 (¼+ ¼) = ½
2. Probability of getting albino offspring (gg) = 2/4 (¼+ ¼) = ½
3. There are 2 possible genotypes among the offspring, which are Gg and gg.
4. There are 2 possible phenotypes among the offspring, which are gray and albino coat color.
5. Probability of getting heterozygous offspring (i.e. Gg) = 2/4 = ½
6. Probability of getting homozygous offspring (i.e. GG or gg) = Probability of getting GG + Probability of getting gg = ½ + 0 = ½
7. The color of the female that was crossed (i.e. Gg), is gray color. The allele for gray coat color (G) is dominant over the allele for albino coat color (g).
8. The color of the male (gg) that was crossed is albino. The recessive allele (g) for albino coat color, in its homozygous state would express itself in the absence of the dominant G allele for gray color.
II. Cross between homozygous gray female with a heterozygous male (GG X Gg):
1. Probability of getting gray offspring (GG or Gg) = 4/4 (i.e. ¼+ ¼ + ¼ + ¼ ) = 1
2. Probability of getting albino offspring (gg) = 0
3. There are only 2 possible genotypes among the offspring, which are GG and Gg.
4. There is only 1 possible phenotype among the offspring, which is gray coat color.
5. Probability of getting heterozygous offspring (i.e. Gg) = 2/4 (i.e. ¼+ ¼ ) = ½
6. Probability of getting homozygous offspring (i.e. GG or gg) = Probability of getting GG + Probability of getting gg = 0 + ½ = ½
7. The genotype of the female that was crossed is GG, given that the female is homozygous gray.
8. The male crossed is a heterozygous male (Gg), the male is gray.
III. Cross between a gray female, whose father was albino, with a heterozygous male (Gg X Gg):
We can make a good guess of the genotype of the female, given that gray color is dominant over albino, and the father was albino (gg). The father can only contribute sperm having only (g) allele, while the mother must contribute only a (G) allele to give a gray offspring. The gray female is definitely heterogyzous female i.e Gg
1. Probability of getting gray offspring (Gg or GG) = ¾ (½ + ¼)
2. Probability of getting albino offspring (gg) = ¼
3. There are 3 possible genotypes among the offspring, which are GG, Gg, and gg.
4. There are 2 possible phenotypes among the offspring, which are gray and albino coat color.
5. Probability of getting heterozygous offspring (i.e. Gg) = 2/4 = ½
6. Probability of getting homozygous offspring (i.e. GG or gg) = Probability of getting GG + Probability of getting gg = ¼ + ¼ = ½
7. The genotype of the female is Gg. We know this because we were given that it is gray in color, and gray is dominant over albino. Also, given that the father was albino (gg), a (g) allele can only be contributed by the father to combine with the dominant (G) allele to give us a female that has heterozygous gray coat color (Gg).
8. The genotype of the male is Gg. We know this because we were given that it was a heterozygous male. If an organism is heterozygous, it has different alleles controlling that trait.
IV. Cross between an albino female, whose father was gray, with a gray male, whose mother was albino (gg X Gg):
The albino female’s genotype is gg, because the g allele is recessive. The gray male’s genotype, whose mother was albino (gg) is definitely Gg, because gray is dominant, and to get a gray offspring, a G allele from the mother of the male must combine with the g allele that the albino father can only contribute i.e. Gg or GG from mother X gg from father = Gg (the gray male offspring).
1. Probability of getting gray offspring = ¼ + ¼ = ½
2. Probability of getting albino offspring (gg) = ¼ + ¼ = ½
3. There are 2 possible genotypes among the offspring, which are Gg, and gg.
4. There are 2 possible phenotypes among the offspring, which are gray and albino coat color.
5. Probability of getting heterozygous offspring (i.e. Gg) = ¼ + ¼ = ½
6. Probability of getting homozygous offspring (i.e. gg or GG) = ½ + 0 = ½
7. The genotype of the gray father of the albino female (gg) is Gg. Of the two possible genotypes of the gray father (i.e. GG or Gg), Gg is the most likely genotype to contribute the recessive g allele that would pair up with another g allele from the mother to give an albino female (gg), i.e. Gg (father) X Gg (Mother) or Gg (Father) X gg (Mother) = gg (albino female)
