Question

lab 6. genetics introduction
name
lab day/time
datasheet
biol 111l
lab section #
list of lower case cursive letters: p = p c = c y = y t = t or t w = w or w
a = a or a s = s g = g or g b = b or b l = l r = r or r e = e
pre - lab practice: monohybrid crosses
in the space below, youll complete monohybrid punnett squares and interpret genotypes and phenotypes. follow the example in the lab intro as a guide.

1. practice writing genotypes

a. when gametes a and a combine, how should the offsprings genotype be written?
b. when gametes a and a combine, how should the genotype be written?

1. cross #1: goofy - colored parakeets

two heterozygous goofy - colored parakeets (gg × gg) are crossed. the g allele is dominant (goofy), and g is recessive (not goofy).
complete the punnett square:
cross: gg x gg
g g
g

g

a. how many of the offspring will show the goofy phenotype? *when asked \how many\ your answer should be written as a fraction.
b. how many will be homozygous dominant (gg)?
c. how many will be homozygous recessive (gg)?
d. what percentage of offspring are not goofy? → ______%

Explanation:

Step1: Determine genotypes for 1.a and 1.b

When a gamete with allele a combines with a gamete with allele A, the genotype is Aa regardless of the order of combination.

Step2: Complete Punnett - square for 2

	G	g
g	Gg	gg

Step3: Calculate Goofy phenotype offspring for 2.a

The Goofy phenotype is determined by the presence of the dominant G allele. Genotypes GG, Gg, and Gg show the Goofy phenotype. So 3 out of 4 offspring show the Goofy phenotype, which is $\frac{3}{4}$.

Step4: Determine homozygous dominant for 2.b

The homozygous - dominant genotype is GG. From the Punnett - square, there is 1 GG out of 4 offspring, so the fraction is $\frac{1}{4}$.

Step5: Determine homozygous recessive for 2.c

The homozygous - recessive genotype is gg. From the Punnett - square, there is 1 gg out of 4 offspring, so the fraction is $\frac{1}{4}$.

Step6: Calculate non - Goofy offspring for 2.d

The non - Goofy phenotype is determined by the gg genotype. There is 1 gg out of 4 offspring. As a percentage, $\frac{1}{4}\times100 = 25\%$.

Answer:

1. a. Aa

b. Aa

1. a. $\frac{3}{4}$

b. $\frac{1}{4}$
c. $\frac{1}{4}$
d. 25%