Genetics Study Guide
Key to Success on the Test
1. What scientist experimented
with pea plants to establish
modern genetics?
• Gregor Mendel
2. What is the difference between a
monohybrid and a dihybrid cross
• Monohybrid examines 1 trait, Dihybrid
examines 2 traits
3. What is the difference between a
gene and an allele?
• Genes are a segment of DNA that code for
a trait. Alleles are alternate forms of that
gene.
• Gene: Pea Pod Color
• Alleles: Yellow pod color or Green pod
color
4. What is the difference between
genotype and phenotype?
• Genotype is the code or letter that
represent a trait
• Phenotype is the physical way that the trait
is expressed
• Genotype: YY
• Phenotype: Yellow
5. What is the difference between
homozygous and
heterozygous?
• Homozygous means that you have 2 same
alleles for a trait (YY or yy)
• Heterozygous means that you have 2
different alleles for a trait (Yy)
6. What is the difference between a
hybrid and a purebred?
• Hybrids have 2 different alleles from the
parent(s) Yy
• Purebreds have two same alleles from the
parent(s) YY or yy
7. What is the difference between
dominant and recessive?
• Dominant alleles have the ability to mask a
recessive allele.
• With the genotypes YY and Yy the
dominant trait will be expressed
• With the genotype yy, the recessive trait
will be expressed
8. What are Punnett Squares used
for?
• To find out the possible outcomes for a
genetic cross
9. Create a Punnett Square for a
monohybrid cross for two
individuals that are
heterozygous for brown eyes
(Bb). Brown eyes are
dominate to blue eyes.
10. Give 3 reasons that Mendel
used pea plants for his studies.
• Short growing period/Easy to Grow
• 7 traits in 2 distinct forms
• Produces many offspring
11. Mendel’s Laws
– The Law of Segregation-During Meiosis
each pair of alleles separate
– The Law of Independent Assortment-gene
pairs separate randomly and independently
of each other
– The Law of Dominance-dominant allele
masks recessive allele
12. What are 3 ways you can show
probability?
• Ratio
• Percent
• Fraction
13. Define trait.
• Anything that can be passed down from
parent to offspring
14. What are carriers?
• Individuals who are heterozygous for a
recessive trait. They carry the trait, but
they are not affected by it.
15. What is a pedigree used for?
• To examine inheritance patterns in
families.
• Circles are females
• Square are males
• Individuals that exhibit the trait are shaded
in
• Individuals that carry the trait are partially
shaded in
16. What is the difference between
sex chromosomes and
autosomes?
• Sex chromosomes determine the sex of
the offspring and X-linked traits.
Autosomes carry the genes that affect the
rest of the individual.
17. What is the genotype for a
female and what is the genotype
for a male
• FEMALE: XX
• MALE: XY
18. What is one difference between
X and Y chromosomes?
• Size. The X chromosome is significantly
larger than the Y chromosome
19. When babies are made, which
gamete controls the sex of the
offspring?
• Male gamete - Sperm
20. What are sex-linked traits?
• Sex-linked traits are from genes located
on the X chromosome of the sex
chromosome.
21. Create a Punnett Square to
show the recessive sexlinked trait “male pattern
baldness” Cross a carrier
female with a normal male.
Give Ratios.
22. What are karyotypes?
• Diagram that shows the cell’s
chromosomes organized from smallest to
largest.
• It allows people to determine gender and
find out if the individual has any
chromosomal disorders.
23. How many chromosomes do
people with Down Syndrome
have?
• 47. They have 3 chromosomes located on
chromosome 21
24. What do you observe about
this karyotype? Is it going to
produce a “normal” offspring?