Genetics: Punnett Squares, Codominance, and Incomplete Dominance

Vocabulary flashcards covering the purpose of Punnett squares, Mendelian complete dominance in tongue rolling, codominance in ABO blood groups, and incomplete dominance in hair texture.

Punnett Square

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

Phenotypic Outcome of an $Rr \times Rr$ Tongue Rolling Cross

Yields a $75\%$ chance of offspring being able to roll their tongue (composed of $25\%$ homozygous dominant $RR$ and $50\%$ heterozygous $Rr$) and a $25\%$ chance of being unable to roll their tongue (homozygous recessive $rr$).

Codominance

An inheritance pattern in which neither allele is dominant over the other, causing both alleles to be fully and simultaneously expressed in the phenotype rather than one masking the other.

Type AB Blood

A codominant blood phenotype produced when an individual inherits an $A$ allele from one parent and a $B$ allele from the other, resulting in full expression of both $A$ and $B$ antigens 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.

Outcome of an $AO \times BO$ Blood Type Cross

A cross between heterozygous type $A$ ($AO$) and heterozygous type $B$ ($BO$) individuals that results in $25\%$ type $AB$ ($AB$), $25\%$ type $A$ ($AO$), $25\%$ type $B$ ($BO$), and $25\%$ type $O$ ($OO$).

Incomplete Dominance

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

Wavy Hair (Incomplete Dominance)

An intermediate, heterozygous phenotype ($Hh$) formed when an individual inherits one allele for straight hair and one allele for curly hair.

Outcome of an $Hh \times Hh$ Hair Texture Cross

A cross resulting in $25\%$ straight hair (homozygous dominant, $HH$), $50\%$ wavy hair (heterozygous, $Hh$), and $25\%$ curly hair (homozygous recessive, $hh$).