Name ______________________________________________________________
Test Date ______________
UNIT 10 - INTRODUCTION TO GENETICS
Although the resemblance between generations of organisms had been noted for thousands of years, it wasn’t until the 1800s
that scientific studies were carried out to develop an explanation for this. Today we know that we resemble our parents
because of _______________, which is the set of characteristics we receive from ______________________. The study of
heredity is known as _________________.
I. SEXUAL REPRODUCTION & MEIOSIS
(pp. 275-278)
In sexual reproduction, an egg and sperm cell fuse together to create a fertilized egg or _______________.
Egg and sperm cells are known as _____________. Gametes are the only cells in the body that are not
produced by ________________. Instead gametes are created through a special process of cell division
called ___________________ which ______________ the chromosome number. Meiosis only occurs in the
_____________ of females and the ___________ of males.
A. Chromosome Number
1. Human _____________ cells, or body cells, contain ________ chromosomes. Somatic cells are
____________ or ________ because these cells contain a ____________ set of chromosomes – half
(______) from __________ and half (______) from __________. These “matching” chromosomes are
known as ________________________________. A homologous pair is a pair of chromosomes – one from each
parent, with the same ____________________ or ____________.
2. Human gametes (___________ and ____________) contain _______ chromosomes. They are
_________________________ or ___________. These cells contain __________ the total number of
chromosomes, a ______________ set of chromosomes. When the gametes fuse together in
_____________________, the resulting _______________ has _______ chromosomes.
B. Meiosis
Gametes are formed in meiosis – a special type of cell division that only occurs in the _______________ of
females and ______________ of males. In meiosis, DNA is replicated once in ______ of _____________, but
the cell goes through two cell divisions, resulting in ______ cells with _______ the original chromosome number.
Meiosis occurs in two stages:
1. Meiosis I - Prior to meiosis I, the DNA is replicated in _____ of ____________________. When the
chromosomes, each consisting of 2 ________________________ line up in the middle of the cell in
________________ I, they line up in __________________ pairs. In anaphase I and telophase I, the
homologous pairs _______________, but the sister chromatids and __________________ are still
intact. Two cells are formed, each with _______ pairs of __________________________ making
up _______ chromosomes, but there are no longer any ______________________________ present,
so the two cells are _________________ or ______.
2. Meiosis II - The process continues with the two cells formed moving directly into prophase II without
any further ____________________________. After the chromosomes align in the middle of the cell in
_________________ II, this time the sister chromatids are pulled apart in _______________ II. Two
new cells are formed from each of the two cells formed in Meiosis I, resulting in a total of ___________
new cells, each with ____________the original number of chromosomes. The cells produced are
called ____________________.
C. Crossing Over
Crossing over occurs during ________________ when __________________ pairs of chromosomes
come together. A portion of one __________________________ may be broken off and exchanged with
the corresponding portion of a sister chromatid of the homologous chromosome. Crossing over is very
common and _____________________ the genetic variability in offspring.
II. HISTORY OF GENETICS
(pp. 263-270)
A. Gregor Mendel – Known as the “Father of _______________”, Mendel is famous for his experiments with
________ plants. He used true-breeding pea plants, which means _________________________ and
characteristics always show. This generation of true-breeding plants is known as ______ generation.
Mendel studied seven ______________, including plant height, seed color, flower color, etc. A trait is an
________________________________. Pea plants cross-pollinate, meaning pollen from one plant
fertilizes an egg from another, but they can also self-pollinate, meaning pollen can fertilize egg from
______________ plant. Mendel controlled the fertilization process of the pea plants by preventing
__________________________________ and controlling ___________________________________.
B. Mendel’s Results
1. P generation – Crossed __________________ plants with one trait with ________________ plants
with the other. For example, _____________________________________________
2. F1 generation – Offspring produced from _________________. In F1, one trait seemed to
_____________. For example, tall plants X short plants = __________________________.
3. F2 generation – Offspring produced from _________________. In F2, trait that disappeared in F1
reappeared in __________ of the offspring; the other ¾ showed _____________________________.
C. Mendel’s Principles – After analyzing his results carefully, Mendel formed conclusions that increased
understanding of inheritance and opened the door for the study of genetics.
1. Individual units called ___________ determine inheritable characteristics. A gene is a portion of ___________
that codes for a specific ____________.
2. For each gene, an organism inherits two alleles, one from each __________________. Alleles are
different forms or ____________________ of a ___________.
a. If the two alleles are the same, the organism is said to be _________________ for that trait and the allele
will be expressed.
b. If the two alleles differ, the organism is said to be ___________________ for that trait and only one allele
will be expressed. The expressed allele is the ______________ allele, designated by an __________-case
letter. The allele that is not expressed in a heterozygous trait is _________________, designated by a
_____________-case letter. A recessive allele is only expressed when an organism is ________________.
3. In meiosis, the two alleles for a trait segregate (_______________). Each egg or sperm cell receives a
copy of one of the two alleles present in the somatic cells of the organism. Due to the random separation of
chromosomes in meiosis, there is a _________ chance that a copy of that allele will end up in the gamete
produced. This is known as the principle of segregation.
D. Genetics Terminology
1. Phenotype - ________________ description of trait; for example, ______________
2. Genotype – Genetic make-up of an organism or set of alleles; for example, ____________________
3. Application of Terminology - If round pea seeds are dominant to wrinkled pea seeds, round is designated
_____ and wrinkled is designated ______.
a. Homozygous dominant for pea seed shape is written ______. Seed shape? __________
Genotype = _____________; Phenotype = __________________
b. Heterozygous for pea seed shape is written _______. Seed shape? _______________
Genotype = _____________; Phenotype = __________________
c. Homozygous recessive for pea seed shape is written _______. Seed shape? _________
Genotype = _____________; Phenotype = __________________
III. ANALYZING INHERITANCE
(pp.135-137)
A. Probability
Due to the law of segregation, if you know the genotype of the parents, you can predict the likelihood of a
trait occurring in the offspring. Probability can be written 3 ways. The probability of a coin coming up
heads after being flipped is (fraction) _____, (ratio) ________, or (percent) _______.
B. Punnett Squares
A Punnett square is a tool used to predict the possible outcomes of _______________ and
____________________; in other words, a Punnett square is used to determine the probability of certain
traits appearing in offspring.
IV. PUNNETT PRACTICE
**Please note: To earn full credit, you must include a key and cross with each problem!**
A. Construct a Punnett square to determine the probability of white flowers if a heterozygous purple (Pp)
flower is crossed with a homozygous white (pp) flower.
Key: _________________________________________
Cross: ________________________________________
Probability of white flowers = ___________________
B. Construct a Punnett square to determine the probability of short pea plants if a homozygous tall (TT)
plant is crossed with a heterozygous tall (Tt) plant.
Key: _________________________________________
Cross: ________________________________________
Probability of short pea plants = _________________
Probability of tall pea plants = ___________________
C. If round peas are dominant over wrinkled peas, make a Punnett square to determine the genotype and
phenotype ratios of the offspring if a heterozygous plant is crossed with a homozygous recessive plant.
Key: _________________________________________
Cross: ________________________________________
Genotype ratio: _________________________________________
Phenotype ratio: ________________________________________
D. Use a Punnett square to determine the genotype and phenotype ratios of the offspring from a cross
between a homozygous dominant yellow pea pea plant and a homozygous recessive green pea pea
plant.
Key: _________________________________________
Cross: ________________________________________
Genotype ratio: _________________________________________
Phenotype ratio: ________________________________________
V. DIHYBRID CROSSES
(pp. 270-271)
The Punnett squares we have been doing are known as ___________________________________,
meaning that only one trait has been considered at a time. In a dihybrid cross, ________ different
____________ on 2 different _____________________ are analyzed.
A. If a pea plant with genotype RRYy (round, yellow peas) is crossed with a pea plant with genotype rrYy
(wrinkled, yellow peas), what would the results be?
Key: R = round, r = wrinkled; Y = yellow, y = green
Cross: ________________________________________
Genotype ratio: ____________________________________________________________
Phenotype ratio: ___________________________________________________________
B. Key: G = gray body
g = black body
R = red eyes
r = black eyes
Cross: GGRr X Ggrr

What are the phenotypes of the parent fruit flies? _________________________________
Cross: __________________________________________
Genotype ratio: _________________________________________________________________________
_____________________________________________________________________________________
Phenotype ratio: ________________________________________________________________________
______________________________________________________________________________________
VI. A CLOSER LOOK AT HEREDITY
(pp. 272, 273)
A. Incomplete Dominance – Neither allele has “complete” dominance over the other - heterozygous
phenotype is a ____________________________________________________
For example, in snapdragons, ____________________________________________________
Cross: ________________________________________
Genotype ratio: _________________________________________
Phenotype ratio: ________________________________________
Cross: ________________________________________
Genotype ratio: _________________________________________
Phenotype ratio: ________________________________________
B. Codominance – Both alleles _____________ dominance and are always __________________ if
present.
For example, ________________________________________________________________________
___________________________________________________________________________________
Cross: ________________________________________
Genotype ratio: _________________________________________
Phenotype ratio: ________________________________________
Cross: ________________________________________
Genotype ratio: _________________________________________
Phenotype ratio: ________________________________________
C. Polygenic Traits – “_________________________” Many traits are controlled by more than one gene.
Examples include _____________________________________________________
D. Multiple Alleles – Many genes have more than ___________ alleles, although an individual only has
_____ alleles for the gene. An example is _______________. There are _______ possible alleles for this gene.
Suggested Study Questions
p. 283 (1-5, 11, 12, 17-20)