# bio 3 problems homework-Cattle coat color is determined

1. Cattle coat color is determined by
codominant alleles R and r. RR results in a reddish cow, Rr in a roan coloured
cow, and rr in a white coloured cow. A population of 4000 cattle consisted of
2560 reds, 1280 roans and 160 white cattle. Calculate the gene frequency of the
‘R’ gene and the ‘r’ gene. If you fill in the Table below youâll have your

Phenotype

Number of cattle

Number of genes

Gene Frequency

R

r

R

r

Red

2560

0

0

Roan

1280

White

160

0

0

Total

4000

Hence
the overall gene frequency (f(p)) of the red gene =
Hence
the overall gene frequency (f(q)) of the white gene =
You
can also solve this question using the Hardy Weinberg formula
2. PKU
(phenylketonuria) occurs in about 1 out of 12,000 Caucasians. It is rarer in
other ethnic groups. Calculate the frequency of the recessive disease causing
gene. Calculate the frequency of the normal gene. Complete the following table:

Human Phenotypes

Number in a population of 12000

Human Genotypes

Number in a population of 12000

Normal

15624

Normal

Carrier

Showing PKU

1

Showing PKU

1

Hint: Here you must
start the answer by calculating the frequency of the homozygous recessive gene
q and you know that homozygous individuals occur in the population once every
12,000 individuals. Hence q2= 1 in
15625.

3.10% of human males in a sampled population were found to be
red/green colorblind. This is a recessive sex-linked condition. What proportion
of human females are expected to be colorblind in this population. Hint: You
might find it easier to answer this question if you referred to the table
below, whereXb is the recessive X-linked colour-blind
allele and XB is the dominant normal gene.

Sex

Category

Homozygous
Dominant

Heterozygous
Dominant

Homozygous
Recessive

FEMALES

Genotype

XB XB

XB Xb

Xb Xb

Phenotype

normal

normal

colour-blind

Gamete
Types

XB

XB and Xb

Xb

MALES

Genotype

XB Y

DOES

Xb Y

Phenotype
(Percentage)

normal
(Then you can fill this in)

NOT

colour-blind
(First you must fill this in)

Gamete
Types

XB and Y

EXIST

Xb and Y