Predicting Genetic Inheritance Flashcards

All 5 cards in this deck

What are the steps to complete a Punnett square for a monohybrid cross?

e.g. $Aa \times Aa$

1. Write one parent's alleles along the top and the other's down the side: $A$, $a$ and $A$, $a$.
2. Fill each box with the row allele + column allele: $AA$, $Aa$, $Aa$, $aa$.
3. Read off the phenotypes: 3 dominant : 1 recessive.

What are the steps to give the outcome of a monohybrid cross as a probability and a percentage?

e.g. a Punnett square giving $AA$, $Aa$, $Aa$, $aa$

1. Count the boxes with the phenotype you want: 1 box out of 4 is $aa$.
2. Write it as a probability: $1/4$ (1 in 4).
3. Convert to a percentage: 25%.

What phenotype ratio is expected when two heterozygous parents are crossed?

e.g. $Aa \times Aa$

3 dominant : 1 recessive — so 25% (1 in 4) show the recessive phenotype.

What is a carrier of a genetic disorder?

A heterozygous person who has one recessive disorder allele, so does not have the disorder but can pass the allele to offspring.

True or false? A Punnett square tells you exactly how many offspring of each type will be produced.

False. It gives the probability (expected ratio) of each genotype and phenotype, not the actual numbers.