Genetics: Punnett Squares, Codominance, and Incomplete Dominance

Vocabulary flashcards covering the core concepts of Punnett squares, Mendelian traits, codominance (ABO blood types), and incomplete dominance (hair types) from Unit 7 Genetics.

Punnett Square

A visual tool used by biologists to determine the statistical likelihood of an offspring inheriting specific alleles from their parents by mapping out all possible genetic combinations.

Purpose of a Punnett Square

To predict the probability of inheriting certain traits rather than analyzing existing medical or DNA samples.

Mendelian Inheritance

A mode of inheritance in which a dominant allele completely masks the presence of a recessive allele in the phenotype.

Heterozygous Tongue-Rolling Cross ($Rr \times Rr$)

A genetic cross involving two heterozygous individuals that results in $25\%$ homozygous dominant ($RR$, will roll tongue), $50\%$ heterozygous ($Rr$, will roll tongue but carries recessive gene), and $25\%$ homozygous recessive ($rr$, will not roll tongue), giving a $75\%$ overall chance to roll the tongue and a $25\%$ chance not to roll.

Codominance

A non-Mendelian inheritance pattern where neither allele is dominant over the other, causing both alleles to be fully and simultaneously expressed in the phenotype.

Type AB Blood

An expression of codominance occurring when an individual inherits an $A$ allele from one parent and a $B$ allele from the other, causing both $A$ and $B$ antigens to be fully expressed on red blood cells.

Type O Blood

A homozygous recessive blood type ($OO$) that occurs when an individual completely lacks both the $A$ and $B$ antigens.

Heterozygous Blood Type Cross ($AO \times BO$)

A cross between a person heterozygous for type A blood ($AO$) and a person heterozygous for type B blood ($BO$), resulting in $25\%$ type AB ($AB$), $25\%$ type A ($AO$), $25\%$ type B ($BO$), and $25\%$ type O ($OO$).

Incomplete Dominance

A pattern of inheritance in which neither allele is completely dominant, resulting in a phenotype that is a blend of both alleles and produces an intermediate trait distinct from either parent.

Hair Type Incomplete Dominance Cross ($Hh \times Hh$)

A cross between two individuals heterozygous for wavy hair ($Hh$) that produces $25\%$ straight hair ($HH$, homozygous dominant), $50\%$ wavy hair ($Hh$, heterozygous intermediate), and $25\%$ curly hair ($hh$, homozygous recessive).