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Chapter 5 Study Guide
Genetics the Science of Heredity
Mendel’s Work
 Gregor Mendel’s work was the
foundation for understanding why
offspring have traits similar to those
of their parents
 Traits are controlled by alleles of
genes. Organisms inherit one allele
from each parent.
 Some alleles are dominant and some
are recessive.
 Probability is the likelihood that a
particular event will happen.
 Mendel was the first scientist to
interpret his data using the principles
of probability
 Geneticists use Punnett squares to
show all the possible outcomes of a
genetic cross.
Human Inheritance
 Some human traits are controlled by a
single gene that has multiple allelesthree or more form.
 Some human traits show a wide range
of phenotypes because these traits are
controlled by many genes. The genes
act together as a group to produce a
single trait.
 Traits are often influenced by the
organism’s environment.
 Males have one X chromosome and
one Y chromosome. Females have
two X chromosomes. Males are more
likely to have sex-linked controlled
by a recessive allele.
 Geneticists use pedigrees to trace the
inheritance pattern of a particular trait
through a number of generations.
Human Genetic Disorders
 Genetic disorders are abnormal
conditions that are caused by
mutations, or DNA changes, in genes
or chromosomes.
Name ___________________ Period ____
 Common genetic disorders include
cystic fibrosis, sickle-cell disease,
hemophilia and Down syndrome.
 Amniocentesis and karyotypes are
tools used to diagnose genetic
disorders.
 Genetic counselors help couples
understand their chances of having a
child with a genetic disorder
Advances in Genetics
 Selective breeding is the process of
selecting a few organisms with
desired traits to serve as the parents
of the next generation.
 Cloning is a technique that produces
genetically identical organisms.
 Genetic engineering can be used to
produce medicines and to improve
food crops. Researchers also use GE
to try to cure human genetic disorders
 DNA fingerprinting can be used to
help determine whether material
found at a crime scene came from a
particular suspect.
 The goal of the Human Genome
Project is to identify the DNA
sequence of every gene in the human
genome.
Key terms:
Trait, Heredity, Genetics, Gene, Allele
Dominant, Recessive, Purebred, Hybrid
Phenotype, Genotype
Homozygous, Heterozygous
Co-dominance, Incomplete Dominance
Punnett Square, Probability
Polygenic Inheritance, Multiple alleles
Sex-linked gene, Carrier
Pedigree, Genetic disorder
Karyotype, Amniocentesis
Selective breeding, Inbreeding,
Hybridization
Clone, Genetic Engineering,
Gene therapy, Genome
Chapter 5 Study Guide
Genetics the Science of Heredity
Name ___________________ Period ____
1. Explain how two organisms with a dominant trait can yield offspring that exhibit the
recessive trait.
2. How can two organisms have the same phenotype but not the same genotype?
3. Explain why traits controlled by recessive alleles on the X chromosome are more
common in males than in females.
4. Why can a person be a carrier of a trait caused by a recessive allele but not of a trait
caused by a dominant allele?
5. Compare and contrast multiple alleles and polygenic inheritance.