Chapter 12 Study Guide: Mendel and Heredity
Section 1 – Origins of Hereditary Science
A. Vocabulary – The following terms are found throughout this chapter. Use
chapter 12 in your textbook to define each term.
1. Cross –
2. Characters (Characteristics) –
3. Trait –
4. Self-pollinate –
5. Cross-pollinate –
6. Monohybrid Cross –
7. Dihybrid Cross -
8. Generation –
9. Parental/P Generation –
10. F1 Generation/First Filial Generation –
11. F2 Generation/Second Filial Generation –
12. Allele –
13. Dominant –
14. Recessive –
15. Phenotype -
16. Genotype –
17. Ratio –
18. Homozygous –
19. Heterozygous –
20. Punnett Square –
21. Probability –
B. Mendel’s Breeding Experiments
1. Who was Gregor Mendel & when did he live?
2. What plants did he work with?
C. Features of Pea Plants
1. How many traits (features) did Mendel’s peas have?
2. Why is the garden pea a good plant to study?
a.
b.
c.
d.
e.
f.
3. What is a hybrid?
D. Mendel’s First Experiments
1. When Mendel crossed a pure/homozygous purple-flowered plant with a
pure/homozygous white-flowered plant, what type of offspring did he
get?
2. When Mendel allowed the offspring from the above cross to breed, what
color flowers did he get? ________________________
3.
E. Ratios in Mendel’s Results
1. Here are Mendel’s actual results of his experiments!
2. How is each of Mendel’s ratios similar? (HINT: Round each RATIO to the
nearest whole number)
Section 2 – Mendel’s Theory
Mendel came to three conclusions at the end of his experiments. These three conclusions
led to the development of a new science that studies heredity; GENETICS.
Explain each of the following:
1. Law of Dominance –
2. Law of Segregation of Alleles –
3. Law of Independent Assortment -
Section 3 – Modeling Mendel’s Laws
A. Using Punnett Squares
1. What does a Punnett square predict?
2. What does a Punnett square show (inside the boxes)?
3. What is written along the top and sides of a Punnett square?
4. What is probability?
5. How can probability be expressed (think math)?
B. Using a Pedigree
1. What is a pedigree and how is it used?
2. Define the term genetic disorder.
3. Why would a couple want to have a pedigree done?
4. What does it mean when someone is a carrier?
5. Define the term albinism.
6. What causes someone to have albinism?
7. Is albinism caused by a dominant or a recessive allele?
8. What 3 aspects of inheritance can a pedigree help identify (what can a
pedigree tell you?
a.
b.
c.
C. Sex-Linked Genes
1. Identify the 2 sex chromosomes. ________ and ________
2. What is a sex-linked gene?
3. Which sex chromosome holds fewer genes? ______ Why?
4. XNXn – represents a female with a dominant (N) allele on one of her X
sex chromosomes a ______________________ (n) allele on the
other X sex chromosome. This makes her a heterozygous carrier for
the recessive trait; she does NOT express the recessive allele in her
phenotype.
5. If a male inherits the Xn chromosome from his mom & the Y
chromosome from his dad, the male will inherit the disorder; there is
no dominant allele on the Y sex chromosome to “mask” the recessive
allele.
6. Two sex-linked genetic disorders in humans are:
a. __________________________- genetic disorder in which a
person cannot distinguish between 2 colors such as red and green.
b. Hemophilia – genetic disorder in which a person’_________________
does NOT clot properly; a serious injury may cause them to bleed to
death.
7. Human males inherit the recessive allele for colorblindness and
hemophilia from their __________________, who gives them their
X sex chromosome. Females don’t usually inherit these diseases
because they inherit two X sex chromosomes; as the dominant allele
on one of the X sex chromosomes “________________” the
recessive disease-causing allele.
Section 4 – Beyond Mendelian Heredity
A. Many Genes, Many Alleles – not all characteristics follow Mendel’s
pattern of inheritance known as complete dominance; other patterns of
inheritance include polygenic inheritance, incomplete dominance,
multiple alleles, and codominance.
1. ________________________ inheritance – occurs when several
genes work together to produce a particular trait. Examples: eye,
skin, hair color and height in humans.
2. ________________________ dominance – pattern of inheritance
where both alleles produce a third phenotype. Example: Cross a red
snapdragon flower (rr) with a white snapdragon flower (ww) produces
a pink snapdragon flower (rw), a third phenotype. If you cross 2 pink
snapdragon flowers rw x rw will produce some
¼ red flowers (rr), ½ pink flowers (rw), ¼ white flowers (ww).
3. ___________________ _______________ - genes that have 3 or
more possible alleles, but the individual only carries 2 of the alleles.
Example in humans is blood type. Identify the 3 genes for the ABO
blood groups:______, ______, ______
a. How many blood types are there? _________
b. Identify the blood types based on their genotypes:
* IAIA or IAi = blood type ______
* IBIB or IBi = blood
type ______
* IAIB = blood type ______
* ii = blood type ______
4. _________________________ - occurs when both alleles for the
trait are expressed in the phenotype. Example: The AB blood type in
humans; the IA allele and the IB allele work are each expressed to give
the ______ blood type. In animals, codominance produces Andalusian
chickens; cross a black rooster and a white hen and the offspring have
black & white feathers.
5. Explain how codominance & incomplete dominance differ from one
another.
B. Genes Affected by the Environment
1. Name 2 environmental conditions that can affect the phenotype of an
organism.
2. Explain, in detail, how temperature affects fur color of the Arctic
fox. How does this benefit the fox?
3. Explain, in detail, how human height may be affected by the
environment.
C. Genes Linked Within Chromosomes – the chromosomes of organisms may
carry several hundred to several thousand genes. The closer genes are to
one another on the same chromosome the ___________ likely they are
to be separated than genes that are _______ apart. Genes, and the
traits they code for, that are close together on the same chromosome
are said to be _______________.