Question

earwax trait example
a man has a genotype of ww. w will be dominant for wet earwax and w will be recessive for dry earwax. this means the man has wet earwax. a woman also has a genotype of ww, and she also has wet earwax. the pair decides to have offspring. the genotype cross is ww x ww. this means it is a cross between two parents who are heterozygous for wet earwax.
genotype = ww x ww
the letters in the parent boxes represent the parents genotypes with both alleles.
the single letters in the boxes on the top of the square represent a single allele from each parent.
the double letters within the square represent alleles of the offspring.

1. fill in the punnett square, and then use that information to complete the chart below.

offspring box number	genotype	phenotype	homozygous or heterozygous
2
3
4

f1 genotypic ratio: __ : : f1 phenotypic ratio: : __

1. what percentage of offspring would have dry earwax? ____
2. what is an allele and how does it relate to a chromosome, a gene, and a trait?

Explanation:

Step1: Fill Punnett - square

	W	w
w	Ww	ww

Step2: Determine genotypes, phenotypes, etc. for each box

• Box 1:
• Genotype: WW
• Phenotype: Wet earwax (since W is dominant for wet earwax)
• Homozygous or Heterozygous: Homozygous
• Box 2:
• Genotype: Ww
• Phenotype: Wet earwax
• Homozygous or Heterozygous: Heterozygous
• Box 3:
• Genotype: Ww
• Phenotype: Wet earwax
• Homozygous or Heterozygous: Heterozygous
• Box 4:
• Genotype: ww
• Phenotype: Dry earwax (since w is recessive for dry earwax)
• Homozygous or Heterozygous: Homozygous

Step3: Calculate ratios

• F1 Genotypic Ratio: WW : Ww : ww = 1 : 2 : 1
• F1 Phenotypic Ratio: Wet earwax : Dry earwax = 3 : 1

Step4: Calculate percentage of offspring with dry earwax

There is 1 ww out of 4 possible genotypes. So the percentage is $\frac{1}{4}\times100\% = 25\%$

Step5: Define allele and its relation

An allele is an alternative form of a gene. Genes are located on chromosomes. Different alleles of a gene can result in different expressions of a trait. For example, the W and w alleles for earwax type are different forms of a gene related to earwax - production, located on a particular chromosome, and they determine the wet or dry earwax trait.

Answer:

Offspring Box Number	Genotype	Phenotype	Homozygous or Heterozygous
2	Ww	Wet earwax	Heterozygous
3	Ww	Wet earwax	Heterozygous
4	ww	Dry earwax	Homozygous

F1 Genotypic Ratio: 1 : 2 : 1
F1 Phenotypic Ratio: 3 : 1

1. 25%
2. An allele is an alternative form of a gene. Genes are on chromosomes. Different alleles can lead to different trait - expressions.