Genetic Inheritance Flashcards

All 8 cards in this deck

What is an allele?

A different form of a gene.

What is the difference between a dominant and a recessive allele?

A dominant allele is always expressed, even if only one copy is present; a recessive allele is only expressed if two copies are present.

What do homozygous and heterozygous mean?

Homozygous = the two alleles for that gene are the same; heterozygous = the two alleles are different.

What is the difference between genotype and phenotype?

Genotype is the combination of alleles an organism has (e.g. $Bb$); phenotype is the characteristic that is expressed.

In a family tree, two parents who do not have a disorder have a child who does. What does this show about the allele causing it?

The allele is recessive, and both parents must be heterozygous carriers.

True or false? Most human characteristics are controlled by a single gene.

False. Most characteristics are the result of multiple genes interacting; only a few, such as red-green colour blindness, are controlled by a single gene.

What are the steps to complete a Punnett square for a monohybrid cross and state the offspring phenotypes?

e.g. $Bb \times Bb$, where B = black fur (dominant) and b = white fur (recessive)

1. Write one parent's gametes along the top, the other's down the side: B and b; B and b
2. Fill the four boxes by combining the alleles: BB, Bb, Bb, bb
3. Read off the phenotypes: 3 black : 1 white

True or false? A cross between two heterozygous parents gives offspring genotypes in the ratio 1 homozygous dominant : 2 heterozygous : 1 homozygous recessive.

True. e.g. $Bb \times Bb$ gives BB, Bb, Bb, bb.