SCIENCE OLYMPIAD HEREDITY 2026/2027 TEST PAPER
QUESTIONS AND SOLUTIONS RATED A+
✔✔chromosome - ✔✔a structure in the nucleus of cells which contains the genes in the
form of DNA.
✔✔DNA - ✔✔a chemical found in the nucleus which contains the cell's genes.
✔✔X chromosome/Y chromosome - ✔✔The chromosomes in humans that determine
the sex of a person. A female possesses two X chromosomes (one from each parent).
A male possessed an X (from his mother) and a Y (from his father) chromosome.
✔✔gene - ✔✔a unit of inheritance that usually is directly responsible for one trait or
character. Each individual has two genes for each trait, one comes from dad and the
other from mom.
✔✔allele - ✔✔alternate forms of a gene. Usually there are two alleles for every gene,
sometimes as many a three or four present in a population.
✔✔homozygous - ✔✔when the two alleles are the same
✔✔heterozygous - ✔✔when the two alleles are different
✔✔dominant - ✔✔a trait (allele) that is expressed irregardless of the second allele -
capital letters
✔✔recessive - ✔✔a trait that is only expressed when the second allele is the same (e.g.
short plants are homozygous for the recessive allele) - lower case letters.
✔✔homozygous dominant - ✔✔both traits are dominant; AA
✔✔heterozygous dominant - ✔✔two different genes; Aa
✔✔test cross - ✔✔cross an individual with the dominant trait expressed with a recessive
indicidual to determine if the individual is homozygous dominant or heterozygous
dominant
✔✔hybrid - ✔✔an individual who has one dominant and one recessive gene for a trait
✔✔incomplete dominance - ✔✔a trait where the phenotype of a hybrid displays a
blending of the two alleles
✔✔phenotype - ✔✔the physical expression of the genes for the trait by an individual
, ✔✔genotype - ✔✔the gene makeup of an organism; phenotype of the trait of an
individual expresses while the genotype is the two genes that cause that trait
✔✔punnett square - ✔✔probability diagram illustrating the possible offspring of a mating
male genes on top of columns and female traits on side of rows
✔✔monohybrid cross - ✔✔a cross involving only one trait (phenotype ratio--3:1 and
genotype ratio 1:2:1)
✔✔dihybrid cross - ✔✔a cross involving two traits. (phenotype ratio-9:3:3:1 and
genotype ratio- 1:2:1:2:4:2:1:2:1)
✔✔probability - ✔✔ratios or percents
✔✔multiple alleles - ✔✔three or more alleles for a gene such as blood type or skin color
✔✔multifactorial traits - ✔✔more than 1 pair of genes plus environment
✔✔codominance - ✔✔both dominant alleles in an individual are expressed such as
blood types
✔✔pleiotrophy - ✔✔the action of an allele affects many parts of the body such as sickle
cell anemia
✔✔variable expressivity - ✔✔an allele can be expressed differently in different people
✔✔sex-linkage - ✔✔allele is located on a sex chromosome and it will be more common
in one gender
✔✔barr bodies - ✔✔tightly coiled x chromosome in females--inactive x chromosome
✔✔calico cats - ✔✔usually on females, yellow and black alleles on x chromosome -
female has 2 X's
✔✔epistasis - ✔✔one pair of genes alters the expression of another pair of genes such
as albino
✔✔pedigree analysis; pedigree - ✔✔a family tree. squares are males and circles are
females
✔✔nondisjunction - ✔✔chromosomes do not separate during meiosis. results in
monosomy and trisomy
QUESTIONS AND SOLUTIONS RATED A+
✔✔chromosome - ✔✔a structure in the nucleus of cells which contains the genes in the
form of DNA.
✔✔DNA - ✔✔a chemical found in the nucleus which contains the cell's genes.
✔✔X chromosome/Y chromosome - ✔✔The chromosomes in humans that determine
the sex of a person. A female possesses two X chromosomes (one from each parent).
A male possessed an X (from his mother) and a Y (from his father) chromosome.
✔✔gene - ✔✔a unit of inheritance that usually is directly responsible for one trait or
character. Each individual has two genes for each trait, one comes from dad and the
other from mom.
✔✔allele - ✔✔alternate forms of a gene. Usually there are two alleles for every gene,
sometimes as many a three or four present in a population.
✔✔homozygous - ✔✔when the two alleles are the same
✔✔heterozygous - ✔✔when the two alleles are different
✔✔dominant - ✔✔a trait (allele) that is expressed irregardless of the second allele -
capital letters
✔✔recessive - ✔✔a trait that is only expressed when the second allele is the same (e.g.
short plants are homozygous for the recessive allele) - lower case letters.
✔✔homozygous dominant - ✔✔both traits are dominant; AA
✔✔heterozygous dominant - ✔✔two different genes; Aa
✔✔test cross - ✔✔cross an individual with the dominant trait expressed with a recessive
indicidual to determine if the individual is homozygous dominant or heterozygous
dominant
✔✔hybrid - ✔✔an individual who has one dominant and one recessive gene for a trait
✔✔incomplete dominance - ✔✔a trait where the phenotype of a hybrid displays a
blending of the two alleles
✔✔phenotype - ✔✔the physical expression of the genes for the trait by an individual
, ✔✔genotype - ✔✔the gene makeup of an organism; phenotype of the trait of an
individual expresses while the genotype is the two genes that cause that trait
✔✔punnett square - ✔✔probability diagram illustrating the possible offspring of a mating
male genes on top of columns and female traits on side of rows
✔✔monohybrid cross - ✔✔a cross involving only one trait (phenotype ratio--3:1 and
genotype ratio 1:2:1)
✔✔dihybrid cross - ✔✔a cross involving two traits. (phenotype ratio-9:3:3:1 and
genotype ratio- 1:2:1:2:4:2:1:2:1)
✔✔probability - ✔✔ratios or percents
✔✔multiple alleles - ✔✔three or more alleles for a gene such as blood type or skin color
✔✔multifactorial traits - ✔✔more than 1 pair of genes plus environment
✔✔codominance - ✔✔both dominant alleles in an individual are expressed such as
blood types
✔✔pleiotrophy - ✔✔the action of an allele affects many parts of the body such as sickle
cell anemia
✔✔variable expressivity - ✔✔an allele can be expressed differently in different people
✔✔sex-linkage - ✔✔allele is located on a sex chromosome and it will be more common
in one gender
✔✔barr bodies - ✔✔tightly coiled x chromosome in females--inactive x chromosome
✔✔calico cats - ✔✔usually on females, yellow and black alleles on x chromosome -
female has 2 X's
✔✔epistasis - ✔✔one pair of genes alters the expression of another pair of genes such
as albino
✔✔pedigree analysis; pedigree - ✔✔a family tree. squares are males and circles are
females
✔✔nondisjunction - ✔✔chromosomes do not separate during meiosis. results in
monosomy and trisomy
