Genetics Test Study Guide
Alleles: alternate forms of a gene for a given trait
Recessive: trait that can be hidden, symbolized by a lower case letter
Dominant: trait that hides another, symbolized by a upper case letter
Genotype: type of alleles an organism has; an organisms genetic make up
Phenotype: outward appearance of a gene
Heterozygous: genotype with two different alleles
Homozygous: genotype with two of the same alleles
Goals of the human genome project: what can the info be used for? To map gene
locations and determine DNA sequence of each gene; could possibly be used against you by
employers, insurance companies, police, etc
Probability—multiplication method:
The probability of having a boy = 1/2, the probability of having a girl = 1/2,
the probability of having 3 girls in a row = ½ x ½ x ½ = 1/8,
Given the parents AaBbCcDc x aabbccdd, what is the probability of getting a child who is
aabbccdd? ½ x ½ x ½ x ½ =1/16
Types of gametes produced by different genotype individuals: use the foil method
AABB can make only AB gametes; AaBb can make AB, Ab, aB, ab; aaBB can make only aB;
AaBB can make either AB or aB
Ideal ratios for monohybrid and dihybrid crosses: monohybrid is from your index cards;
dihybrid: AaBb x AaBb you get a 9:3:3:1; AAbb x aaBB you get 16/16 AaBb
Tay-sachs disease: caused by an autosomal recessive gene
Sex determination: male determines the sex in humans since they are heterozygous (XY)
for the sex chromosomes; they give their X to their daughters and their Y to their sons;
in chickens female determines the sex since she is heterozygous (ZW)
Sex-linkage; presence of traits in males vs. females: Mothers give an X chromosome to
both sexes of offspring; males only get 1 X (from Mom) so if they get 1 recessive allele
they show the recessive trait; females get an X from both parents so they need to get 2
recessive alleles to show the recessive traits; females can be carriers if they are
heterozygous
Human blood types: know the chart in your lecture notes for the genotypes and
phenotypes
Examples of polygenic traits: controlled by more than 1 gene; examples are eye color, skin
color, height in humans
Pedigree chart: be able to determine the genotype of individuals on a pedigree chart
Non-disjunction: failure of chromosome pairs to separate in meiosis; causes gametes with
an abnormal number of chromosomes