Download C. Crossing Over

Name ________________
Test Date ___________UNIT
8 – Meiosis & 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 _________________.
What type of cells
undergoes Meiosis?
What type of cells
undergoes Mitosis?
What is a gamete?
Give examples.
If 2n= 800, than
n=________
What are homologues
pairs of chromosomes?
What is the end result
of Meiosis?
How is Meiosis
different compared to
Mitosis?
What is crossing over?
What is a benefit to
crossing over?
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.
Unit 8- HISTORY
OF GENETICS
Why is Gregor Mendel
known as the “Father
of Genetics”?
Define & Give an
example of a trait.
What is the difference
between crosspollination and self –
pollination?
If your parents were
the F1 generation, who
would be the P
generation, and who
would be the F2
generation?
Read about Gregor Mendel (pp. 263-270) and write at least 8 characteristics about him around
his picture.
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.
What are alleles?
1. Individual units called ___________ determine inheritable characteristics. A gene is a
portion of ___________ that codes for a specific ____________.
If you have 2 of the
SAME alleles you are
considered
_______________, if
you have 2
DIFFERENT alleles,
you are ___________
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.
What is the difference
between dominant &
recessive traits?
What terminology
would be described if I
said “The dog was
black” ?
What terminology
would be descried if I
said “ The dog was
BB”?
Describe the Principle
of Segregation in your
own words.
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: _________________________
Genotype ratio: = ___________________
Phenotype ratio:= ___________________
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: ___________________
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: _________________
B. Codominance – Both alleles _____________ dominance and are always __________________ if
present.
For example, ________________________________________________________________________
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)