8a Monohybrid Crosses Flashcards
What is a monohybrid cross?
Definition: A monohybrid cross is a genetic cross between two individuals focusing on a single trait with contrasting alleles.
Purpose: It is used to determine the dominance relationship between two alleles.
What is a Punnett square?
Definition: A Punnett square is a diagram used to predict the genotype and phenotype combinations of offspring from a genetic cross.
Function: It helps visualize the possible genetic outcomes and their probabilities.
Can you complete an autosomal complete dominance Punnett square?
Definition: A Punnett square for autosomal complete dominance involves alleles where one allele is completely dominant over the other.
Example: Crossing a homozygous dominant (AA) with a heterozygous (Aa) individual.
A (Parent 1) A (Parent 1)
A (Parent 2) AA AA
a (Parent 2) Aa Aa
Genotypes: 50% AA, 50% Aa
Phenotypes: 100% dominant trait expressed
Can you complete an autosomal codominance Punnett square?
Definition: A Punnett square for autosomal codominance involves two alleles that are both fully expressed in the heterozygous state.
Example: Crossing a heterozygous individual with blood type AB (IAIB) with another heterozygous individual with blood type AB (IAIB).
IA (Parent 1) IB (Parent 1)
IA (Parent 2) IAIA IAIB
IB (Parent 2) IAIB IBIB
Genotypes: 25% IAIA, 25% IAIB, 25% IBIB, 25% IAIB
Phenotypes: 25% Type A, 50% Type AB, 25% Type B
Can you complete a sex-linked Punnett square?
Definition: A Punnett square for a sex-linked trait involves genes located on the sex chromosomes (X or Y).
Example: Crossing a female carrier for hemophilia (XHXh) with a normal male (XHY).
XH (Mother) Xh (Mother)
XH (Father) XHXH XHXh
Y (Father) XHY XhY
Genotypes: 25% XHXH, 25% XHXh, 25% XHY, 25% XhY
Phenotypes: 50% non-carrier females, 25% carrier females, 25% affected males
What is a monohybrid test cross? Can you display this in an example?
Definition: A monohybrid test cross involves breeding an individual with a dominant phenotype (but unknown genotype) with a homozygous recessive individual to determine the unknown genotype.
Example: If a plant with dominant phenotype (purple flowers) and unknown genotype (PP or Pp) is crossed with a plant with recessive phenotype (pp), the offspring’s phenotype ratio can reveal the genotype.
P (Unknown) P (Unknown)
p (Test) Pp Pp
p (Test) Pp Pp
Outcomes:
If all offspring are purple (Pp), the unknown parent was PP.
If there are purple (Pp) and white (pp) offspring, the unknown parent was Pp.
What does the term ‘pure-breeding’ mean?
Definition: Pure-breeding refers to organisms that are homozygous for a specific trait and consistently produce offspring with the same phenotype when self-fertilized or crossed with another pure-breeding organism for that trait.
Example: A plant that is homozygous dominant (AA) or homozygous recessive (aa) for flower color is considered pure-breeding for that trait.
