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Name: _____________________________________
Guided Reading – Chapter 14-15
Date: __________________
Chapter 14
1. Define the following terms:
a. Character
A heritable feature that varies among individuals (a characteristic).
b. Trait
Each variant for a character (each phenotype).
c. True-breeding
Plants that produce the same phenotypes in their offspring as themselves.
d. Hybridization
Crossing two different true-breeding populations.
e. P generation
The parental generation.
f. F1 generation
Offspring of the P generation – the first filial generation.
g. F2 generation
Offspring of the F1 generation – the second filial generation.
h. Alleles
Versions of genes.
i. Punnett Square
A visual way to analyze the possibilities and probabilities of a genetic cross.
j. Homozygous
Having two of the same allele at the same locus on homologous chromosomes.
k. Heterozygous
Having two different alleles at the same locus on homologous chromosomes.
l. Phenotype
The outward appearance of an organism.
m. Genotype
The underlying alleles that generate an organism’s phenotype.
2. In your own words, what is Mendel’s Law of Segregation?
Chromosomes separate into gametes so that each gamete contains only one allele for each
trait.
3. What is the Law of Independent Assortment and how does this “law” relate to meiosis?
The segregation of chromosomes/alleles happens at random during Metaphase I/II.
Exception: Linked genes.
4. Write your own example for the Law of Independent Assortment.
A purple-flowered (but white carrier) pea plant undergoing Metaphase I/II will see its alleles
distributed randomly such that one gamete may receive a purple allele and one a white allele.
5. Define and then explain in your own words both the Rules of Multiplication and the Rules
of Addition.
The Rule of Multiplication states that the probability of all of two or more events happening
together can be found by multiplying their individual likelihoods. The probability of any of
two or more events can be found by adding their individual likelihoods as part of the Rule of
Addition.
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Adapted from L. Miriello by S. Sharp
Name: _____________________________________
Guided Reading – Chapter 14-15
Date: __________________
6. Contrast codominance and incomplete dominance.
Codominance occurs when the parents of a cross are both genotypes
7. Why do we need to look at genetics at both organismal and the molecular level?
The organismal level helps us determine dominance when analyzing phenotypes, but it is on
the molecular level that the alleles actually function.
8. Does having a dominant allele mean that it will be found in greater frequency in the
population?
Frequently but not always. Consider Huntington’s disease and other dominant-allele diseases.
9. What are multiple alleles?
When more than two alleles control inheritance for a single trait.
10. What does the term pleiotropy mean?
When a single gene can have multiple phenotypic effects (usually a disease).
11. In your own words, explain epistasis.
When a gene can mask the expression of another gene/trait – not merely a trait masking
another trait as in dominant/recessive. There is no visible trait for one character because
another trait masked/blocked it.
12. What would be your “clue” that a character would have polygenic inheritance pattern?
The phenotypes are not categorical. Instead, there is a range of phenotypes across a
spectrum, like height.
13. What is a pedigree and how does it help in our understanding of genetics?
A pedigree is a genetic family tree. It helps us understand the flow of genes through
generations and can aid in determining genotypes as well as inheritance patterns.
14. Describe and discuss the genetics of the following inherited disorders:
a. Cystic Fibrosis
A recessive autosomal mutation on Chromosome 7 leads to malfunctioning CFTR
(chloride) channels. Mucus builds up outside the cell.
b. Sickle cell disease
A narrowing of red blood cells that reduces oxygen-binding capacity, caused by a recessive
X-linked allele.
c. Achondroplasia
Dwarfism, which has a lethal dominant inheritance pattern. Two dominant alleles leads
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Adapted from L. Miriello by S. Sharp
Name: _____________________________________
Guided Reading – Chapter 14-15
Date: __________________
to death (lethal dominant inheritance).
d. Huntington’s disease
A dominant allele that leads to a degenerative brain/nervous system disorder.
15. Contrast amniocentesis and chorionic villus sampling
Amnio = amniotic fluid withdrawn to obtain fetal cells.
CVS = fetal cells harvested from chorionic villi.
Chapter 15
16. What is the chromosomal basis of inheritance?
Chromosomes carry the alleles that give us our traits at specific locations. They are the
vehicle for the alleles as discovered by Mendel.
17. What does wild type mean?
The “normal phenotype.”
18. Why was Morgan’s choice of fruit fly such a good one for genetic experiments?
There are only four pairs of chromosomes and the flies breed prolifically.
19. How did Morgan associate traits with the sex of the fruit fly?
Mendel found a correlation between white-eyed phenotypes and gender. Males more
frequently had white eyes (w), whereas females more frequently had the wild-type phenotype
(w+).
READ THIS: Be careful with the way the letters represent the traits – the + superscript means the
trait is absent – “vg+” means normal wings, not vestigial wings. This is counterintuitive and appears
backwards – be careful with it while you read or you will get VERY confused.
20. What does it mean when genes are linked or we can say there is linkage?
Genes are located close to one another on a chromosome and tend to be inherited together.
READ THIS: The word recombinant is critical. Recombinants are the traits that are in the offspring
“mixed and matched,” meaning (think of it in terms of peas) round and yellow parents crossed with
wrinkled and green seeds. The offspring that are round and yellow OR green and wrinkled ARE NOT
recombinants. The offspring that are yellow and wrinkled OR green and round ARE recombinants.
The parental genes are thus “mixed and matched.” Understanding this term is essential.
21. In what step of meiosis would recombinants form and why?
Recombinants form in Prophase I during crossing over (synapsis).
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Adapted from L. Miriello by S. Sharp
Name: _____________________________________
Guided Reading – Chapter 14-15
Date: __________________
22. What is the difference between a genetic map, a linkage map and a cytogenetic map?
A genetic map shows the genetic loci on a chromosome. A linkage map is similar but is based
on frequencies of recombination. A cytogenetic map is also similar but is based on visual
approximations of gene locations from chromosome staining.
23. Explain the chromosomal basis of sex determination in the following organism:
a. Mammals
XY determination.
b. Grasshoppers
X0 determination. Females are XX, males are just X (X0).
c. Birds and some fish
ZW determination. Males are ZZ, females are ZW.
d. Bees and ants
Haplodiploid – many individuals have no sex chromosomes. Males are haploid and
females are diploid.
24. What is the SRY gene and why is it important?
SRY is a gene found on the Y chromosome. Its activation leads to the development of male sex
organs and gender differentiation.
25. What is a sex-linked gene?
A gene found on a sex chromosome (usually X).
26. What is X inactivation?
When one X chromosome is unused in female (XX) karyotypes. The unused chromosome
becomes a Barr body.
27. Why are most Calico cats female?
The gene for black/orange fur is found on the X chromosome, so mostly only females can
receive each allele (one for each black/orange color). The white color that is the final color to
achieve a Calico phenotype is found on another chromosome.
28. What is nondisjunction and when in meiosis can it occur?
Nondisjunction is an uneven separation of chromosomes and occurs during
metaphase/anaphase (either I or II).
29. Define the following terms:
a. Aneuploidy
An abnormal chromosome number.
b. Monosomic
When one of a pair of chromosomes is missing (as in Turner Syndrome).
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Adapted from L. Miriello by S. Sharp
Name: _____________________________________
Guided Reading – Chapter 14-15
Date: __________________
c. Polyploidy
Having more than two sets of chromosomes (3n, 4n, 8n, et cetera).
30. Label the following alterations in chromosomal structure. Define the term alongside the
diagram. These terms will be used in the coming chapters.
Deletion – a section of a
chromosome is removed.
Duplication – a section of a
chromosome is copied.
Inversion – a section of a
chromosome is flipped.
Translocation – a section of
a chromosome is added to a
different chromosome.
31. Explain the following human disorders that result from chromosomal alterations.
a. Down Syndrome
Nondisjunction leads to three copies of Chromosome 21.
b. Klinefelter Syndrome
Nondisjunction leads to two copies of the X chromosome and one Y chromosome.
c. Turner Syndrome
Nondisjunction leads to only one copy of the X chromosome.
d. CML
Chronic mylogenous leukemia – a section of a chromosome is translocated.
e. Cri du Chat
A section of Chromosome 5 is duplicated, leading to developmental disorders and
underdeveloped larynxes.
32. What is genomic imprinting?
When one copy of an allele is randomly silenced by methylation.
33. What are extranuclear genes?
Genes found outside the nucleus, like in mtDNA.
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Adapted from L. Miriello by S. Sharp
Name: _____________________________________
Guided Reading – Chapter 14-15
Date: __________________
34. What are two diseases carried in (maternal) mitochondrial DNA?
Leber hereditary optic neuropathy (LHON)
Pearson syndrome
Leigh syndrome
Pyruvate dehydrogenase complex deficiency (PDCD/PDH)
Progressive external opthalmoplegia
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Adapted from L. Miriello by S. Sharp