An experiment to determine the inheritance of fur color mates two mice. A true b

Question

An experiment to determine the inheritance of fur color mates two mice. A true breeding mouse with purple hair is crossed with a true breeding mouse with red hair. All the offspring (F1 generation) are purple.

A) Based on this, what is the dominant trait and the recessive trait?

B) What is the genotype of all of the F1 generation?

The F1 animals are crossed and produce the following (F2) progeny.

290 purple mice

110 red mice

C. Do these numbers make sense?.. What is your hypothesis that would explain the ratio of the F2 progeny?

D. Use a Chi-square test to determine whether those numbers fit a Mendelian pattern of inheritance

Explanation / Answer

A) As both the true breeding mouse shall be homozygous, we can hereby say that the allele for purple colour is dominant as all the mice in F1 generation are purple. Hence allele for red colour is recessive.

B) All mice in the F1 generation shall be heterozygous as the both the parents are homozygous with different alleles.

C) According to Mendelian genetics, 3/4 of mice in F2 generation should be with the dominant trait, i.e. purple colour and 1/4 should be with red colour. As the numbers are pretty close, the inheritance pattern is following Mendelian genetics.

D) Observed values for purple colour – 290

Observed values for red colour – 110

Expected values for purple colour – 300

Expected values for red colour – 100

Applying the chi test formula, (Observer – Expected) ^2/Expected, for both phenotypes and adding them, we get, 1.33. Referring to the value of chi-square function for 1 degree of freedom in the critical value table, we find out that P value is less than 0.1, or 10 percent. We reject a hypothesis when it has a value greater than that of 5 percent in the critical value table. Hence, our case follows Mendelian genetics.

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