Modern Genetics
Table of Contents
Human Inheritance
Human Genetic Disorders
Advances in Genetics
Modern Genetics
Patterns of Human Inheritance
1. Single genes with two alleles
Ex: widow’s pick
Figure 2 Punnett Square
Modern Genetics - Human Inheritance
Patterns of Human Inheritance
• Single genes with multiple alleles
Ex: Inheritance of Blood Type
Blood type is determined by a single gene with three
alleles.fig3/146
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Patterns of Human Inheritance
• Traits controlled by many genes
• Ex: human height
• Discovery activity/p144
Modern Genetics - Human Inheritance
The Sex Chromosomes
The sex chromosomes carry genes that determine whether a
person is male or female. They also carry genes that
determine other traits.
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The Sex chromosomes
Sex-linked genes- genes on the X and Y chromosomes
• not always the same
• Can have dominant and recessive alleles
• Because males have only one X chromosome, male are
more likely to have a sex linked trait that is controlled by
recessive alleles.
Female -2X
Male 1X, 1Y
Modern Genetics - Human Inheritance
Colorblindness Punnett Square
Red-green colorblindness is a sex-linked trait. A girl who
receives only one recessive allele (written Xc) for red-green
colorblindness will not have the trait. However, a boy who
receives one recessive allele will be colorblind.
Modern Genetics - Human Inheritance
Identifying Main Ideas
As you read the section “Patterns of Human Inheritance,”
write the main idea in a graphic organizer. Then write three
supporting details that further explain the main idea.
Main Idea
Human traits are controlled by single genes with two alleles, single
genes with multiple alleles, and multiple genes.
Detail
Detail
Detail
Human traits
controlled by single
genes with two
alleles have two
distinctly different
phenotypes.
Though a single
gene can have
multiple alleles, a
person can carry
only two of these
alleles.
Multiple genes that
control a trait act
together to produce
a single trait with a
large number of
phenotypes.
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The effect of environment
• Many of a person’s characteristics are determined by an
interaction between genes and the environment
Modern Genetics - Human Inheritance
Links on Genetics
Click the SciLinks button for links on genetics.
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End of Section:
Human
Inheritance
Modern Genetics
Human Genetic Disorders
Genetic disorder- abnormal condition that a person inherits
through genes or chromosomes
Causes:
• Mutations in the DNA of genes
• Changes in the structure of chromosoms
• Changes in the number of chromosomes
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Human Genetic Disorders
• Cystic Fibrosis- body produces abnormally thick mucus in
the lungs or intestines
• Cause by a recessive allele on one chromosome as a
result of a mutation in which three bases are removed
from a DNA molecule
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Human Genetic Disorders
Sickle –Cell Disease
• Affects hemoglobin, a protein in the red blood cells that
carries oxygen; cells clog blood vessels
• The allele is codominant with normal allele
• A person with two sickle cell alleles will have the disease
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Human Genetic Disorders
Hemophilia
• Person’s blood clots very slowly or nor at all
• Caused by a recessive allele on the X chromosome
• Sex-linked disorder/occurs more in male than in females
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Human Genetic Disorders
Down Syndrome
• A person’s cell have an extra copy of chromosome 21 ( 3
chromosomes)
• Occurs when chromosomes fail to separate properly
during meiosis
• Effect: some degree of mental retardation; heart defects
Modern Genetics - Human Genetic Disorders
A Pedigree
A pedigree is a chart or “family tree” that tracks which
members of a family have a particular trait.
Modern Genetics - Human Genetic Disorders
A Hemophilia Pedigree
The pedigree shows the inheritance of hemophilia, a sexlinked disorder in a family.
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Managing Genetic Disorders
• Karyotypes- picture of all the chromosomes in a cell
• Genetic counseling- understand the chances of having a
child with a particular genetic disorder
• Dealing with genetic disorders
Modern Genetics - Human Genetic Disorders
Pedigree Activity
Click the Active Art button to open a browser window and
access Active Art about pedigrees.
Modern Genetics - Human Genetic Disorders
Comparing and Contrasting
As you read, compare and contrast the types of genetic
disorders by completing a table like the one below.
Disorder
Cystic fibrosis
Description
Cause
Body produces
abnormally thick
mucus.
Red blood cells are
sickle-shaped and have
reduced ability to hold
oxygen.
Recessive allele due to
removal of three DNA
bases
Hemophilia
Blood clots slowly or not
at all.
Recessive allele on X
chromosome
Down Syndrome
Mental retardation and
heart defects
An extra copy of
chromosome 21
Sickle-cell disease
Codominant allele
Modern Genetics - Human Genetic Disorders
Sickle-Cell Disease
Click the Video button to watch a movie about
sickle-cell disease.
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End of Section:
Human Genetic
Disorders
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Advances in Genetics
• Selective Breeding: selecting organisms with desired traits
to be parents of the next generation
• Inbreeding: crossing two individuals that have the similar
Characteristics
Hybridization: crossing two genetically different individuals;
the offspring will have the best traits from both parents
Modern Genetics - Advances in Genetics
Changing Rice Production
The graph shows how worldwide
rice production changed
between 1965 and 2000. New,
hybrid varieties of rice plants are
one factor that has affected the
amount of rice produced.
Modern Genetics - Advances in Genetics
Changing Rice Production
Reading Graphs:
According to the graph, how
did rice production change
between 1965 and 2000?
Rice production increased.
Modern Genetics - Advances in Genetics
Changing Rice Production
Reading Graphs:
How many metric tons of rice
per hectare were produced in
1965? How many were
produced in 2000?
2 in 1965; 4 in 2000
Modern Genetics - Advances in Genetics
Changing Rice Production
Calculating:
Calculate the approximate
difference between rice
production in 1965 and 2000.
2 metric tons/hectare
Modern Genetics - Advances in Genetics
Changing Rice Production
Developing Hypotheses:
What factors besides new
varieties of plants might help
account for the difference in
rice production between 1965
and 2000?
Possible answer: fertilizers
and improved harvesting
methods
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Cloning
• Organism that have • Is cloning ethical?
the exact genes as
the organism from
which it was produced
Modern Genetics - Advances in Genetics
Genetic Engineering
Scientists use genetic engineering to create bacterial cells
that produce important human proteins such as insulin.
Modern Genetics - Advances in Genetics
Asking Questions
Before you read, preview the red headings. In a graphic
organizer like the one below, ask a question for each
heading. As you read, write answers to your questions.
Questions
What is selective breeding?
Answers
Selective breeding is the process of
selecting organisms with desired traits
to be parents of the next generation.
Why are organisms cloned?
To produce offspring with desired traits
What is genetic engineering?
A process in which genes from one
organism are transferred into the DNA
of another organism
What advance has helped us learn
about human genetics?
The Human Genome Project
Modern Genetics - Advances in Genetics
Links on Genetic Engineering
Click the SciLinks button for links on genetic engineering.
Modern Genetics - Advances in Genetics
Selective Breeding
Click the Video button to watch a movie about
selective breeding.
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End of Section:
Advances in
Genetics
Modern Genetics
Graphic Organizer
Human traits
controlled by
Single genes
Multiple
alleles
Many genes
Sex-linked
genes
such as
such as
such as
such as
Widow's peak
Blood type
Height
Colorblindness
Modern Genetics
End of Section:
Graphic Organizer