Download Human Heredity

Queen Victoria was a Hemophiliac?
The Human Genome
Human reproduction and development
are influenced by factors such as gene
expression, hormones, and the
environment.
Interest Grabber
Section 14-1
To
A Family Tree
understand how traits are passed on from generation to generation, a
pedigree, or a diagram that shows the relationships within a family, is
used. In a pedigree, a circle represents a female, and a square represents
a male. A filled-in circle or square shows that the individual has the trait
being studied. The horizontal line that connects a circle and a square
represents a marriage. The vertical line(s) and brackets below that line
show the child(ren) of that couple.
1.This pedigree shows the inheritance of attached ear lobes. Which parent has attached ear lobes?

2.How many children do the parents have? Which child has attached ear lobes?

3.Which child is married? Does this child’s spouse have attached ear lobes? Do any of this child’s children
Gohave
to attached ear lobes?
Section:

Human Traits



Remember: Human traits are inherited
according to Mendel’s principles:
Principles of Dominance and Segregation
Pedigrees are used to study how traits
are passed from one generation to the
next.
However, most human traits are
impossible to trace as single genes.
Remember:
 Many human traits are polygenic =
many genes control a single trait
 Phenotypes are influenced by
genotypes and the environment.
Figure 14-3 A Pedigree
Section 14-1
A circle represents
a female.
A horizontal line connecting
a male and female
represents a marriage.
A half-shaded circle
or square indicates
that a person is a
carrier of the trait.
A completely
shaded circle or
square indicates
that a person
expresses the
trait.
Go to
Section:
A square represents
a male.
A vertical line and a
bracket connect the
parents to their children.
A circle or square
that is not shaded
indicates that a
person neither
expresses the trait
nor is a carrier of
the trait.
What do these pictures show you?
How are they different?
Human Chromosomes



Cell biologists photograph cells in mitosis, then
cut out the chromosomes and pair them up.
Karyotype = picture of organized chromosomes
Human cells contain 46 chromosomes (23 pairs)


44 chromosomes are autosomal chromosomes or
autosomes
2 chromosomes are known as sex chromosomes,
because they determine an individual’s sex.


Females have two X chromosomes (46XX)
Males have one X and one Y chromosome (46XY)
Men vs. Women

There are about an equal number of men and
women, because of the way the sex
chromosomes separate during meiosis resulting
in a 50:50 chance of having a male or female
child



All egg cells have a single X chromosome (23X)
Half of all sperm have an X (23X) and the other half
of sperm have a Y (23Y)
So about half of all zygotes will be 46XX and the
other half of zygotes will be 46XY
Human Genes


The human genome includes tens of
thousands of genes and the DNA
sequence on these genes determines
many characteristics.
Gene mapping is the process of identifying
the trait each gene is responsible for on
each chromosome.
Blood Type Genes

The best known genes responsible for human blood are
the ABO groups and the Rh groups

Rh is determined by a single gene with two alleles (positive or
negative).



Rh+ is dominant, so people with Rh+/ Rh+ or Rh+/Rh- are Rh
positive.
Rh- is recessive, so people with Rh-/Rh- are Rh negative.
ABO is determined by three alleles IA, IB and i. The alleles
produce antigens on the surface of red blood cells.


IA and IB are codominant, so people with IA and IB produce both
antigens, making blood type AB
i is recessive, so people with IA IA or IAi produce A antigens, making
blood type A, people with IB IB or IBi produce B antigens, making
blood type B, and people with ii produce no antigens, making blood
type O
Figure 14-4 Blood Groups
Section 14-1
Phenotype
(Blood Type
Go to
Section:
Genotype
Antigen on
Red Blood Cell
Safe Transfusions
To
From
Do Now

With a partner, answer the following:



What is the difference between a genetic
disorder and a chromosomal disorder?
Identify at least one genetic disorder.
Identify at least one chromosomal disorder.
This is a picture from the 1900’s.
Do you see anything interesting?
The Fugates from Kentucky
The Fugates from Kentucky



Methemoglobinemia is a recessive gene,
which means it can only be passed on if
both parents carry the gene.
So the chances of Martin Fugate meeting
and marrying someone who carried the
‘blue’ gene were pretty slim, but that’s
what happened.
Martin Fugate and Elizabeth Smith went
on to have seven children, four of them
reported to be blue.
Genetic Disorders

Many genes have been studied and
identified through the study of genetic
disorders caused by a small change in the
DNA of a gene

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Recessive allele genetic disorders
Dominant allele genetic disorders
Codominant allele genetic disorders
Recessive Alleles

Some genetic disorders are caused by two
recessive alleles being brought together
and expressed in an individual
(homozygous recessive).

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Albinism
PKU (phenylketonuria)
Tay-Sachs disease
CF (cystic fibrosis)
Diabetes
Dominant Alleles


Remember: a dominant allele is expressed
even when a recessive allele is also
present.
Some genetic disorders are caused by a
dominant allele


Dwarfism (achondroplasia)
Huntington’s disease
Codominant Alleles

Some genetic disorders are caused by two
dominant alleles being brought together
and expressed in an individual
(homozygous dominant).

Sickle cell disease
Human Chromosomes


The arrangement of genes on
chromosomes affects gene expression and
development.
Remember: Genes on the same
chromosome are linked (inherited
together), or may be separated by
crossing-over during meiosis
Sex-linked Genes

Genes located on the X or Y
chromosomes are said to be
sex-linked.


Many sex-linked genes are
found on the X chromosome,
the smaller Y chromosome
contains only a few genes.
Since males have just one X
chromosome, X-linked alleles
are expressed in males, even if
their recessive



Colorblindness
Hemophilia
Duchenne Muscular Dystrophy
Figure 14-13 Colorblindness
Do Now: Take out Human Genome notes (Disorders)
Section 14-2
Complete the following Punnett Square
Father
(normal vision)
Colorblind
Normal
vision
Male
Female
Daughter
(normal vision)
Son
(normal vision)
Daughter
(carrier)
Son
(colorblind)
Mother
(carrier)
Go to
Section:
Figure 14-13 Colorblindness
Section 14-2
Father
(normal vision)
Colorblind
Normal
vision
Male
Female
Daughter
(normal vision)
Son
(normal vision)
Daughter
(carrier)
Son
(colorblind)
Mother
(carrier)
Go to
Section:
X-Chromosome Inactivation



Since men survive with just one X
chromosome, how does a female adjust to
survive with the extra X chromosome?
In female cells, one X chromosome is
randomly switched off, forming a Barr body.
For example, tricolor cats are almost always
females!
What do you notice about this
karyotype?
Trisomy 21 = Down Syndrome
Chromosomal Disorders

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Sometimes, an error in meiosis occurs when
homologous chromosomes don’t separate =
nondisjunction (“not coming apart”)
This results in abnormal numbers of
chromosomes in gametes, and chromosomal
disorders may result in offspring.


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Down syndrome (trisomy 21)
Turner’s syndrome (females with XO)
Klinefelter’s syndrome (males with XXY, XXXY, or
XXXXY)
Interest Grabber
Section 14-2
Gender Benders
You
may remember that in humans, the sperm cells
may carry an X chromosome or a Y chromosome, while
egg cells have only X chromosomes. Sometimes, errors
during meiosis in one of the parents produce offspring
with an abnormal number of sex chromosomes.

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1.On a sheet of paper, construct a Punnett square for the following cross: XX x XY. Fill
in the Punnett square. What does the Punnett square represent? According to the
Punnett square, what percentage of the offspring from this genetic cross will be
males? What percentage will be females?
2.On a sheet of paper, construct a Punnett square for the following cross: XXX x XY.
Fill in the Punnett square. How is this Punnett square different from the first one you
constructed? What might have caused this difference?
3.How do the offspring in the two Punnett squares differ?
X
Y
X
What percentage of the offspring
will be males? What percentage
will be females?
X
X
How do the offspring in the
two Punnett squares differ?
What might have
caused this difference?
XX
O
Y
Nondisjunction
Section 14-2
Homologous
sex
chromosomes
fail to separate
Meiosis I:
Nondisjunction
Go to
Section:
Meiosis II
Nondisjunction
Section 14-2
Homologous
sex
chromosomes
fail to separate
Meiosis I:
Nondisjunction
Go to
Section:
Meiosis II
Nondisjunction
Section 14-2
Homologous
sex
chromosomes
fail to separate
Meiosis I:
Nondisjunction
Go to
Section:
Meiosis II
Human Genes and Chromosomes

In a human diploid cell, there are more
than 6 billion nucleotide pairs of DNA

Since chromosomes 21 & 22 are the smallest,
they were the 1st sequenced

Chromosome 22 contains about 43 million DNA
bases making up 545 different genes


Genetic disorders on chromosome 22 include an allele for
leukemia and neurofibromatosis.
Chromosome 21 contains about 32 million DNA
bases making up 225 different genes

Genetic disorders on chromosome 21 include an allele for
Lou Gehrig’s disease.
Do you see anything unusual
about this picture?
Watch this scene from “Gattaca”

On a separate piece of paper, write a
reaction to this scene.




When would this be necessary?
How can this be misused?
What limits should be established?
What future issues may arise?
Human Molecular Genetics



The human genome is all of the human
genetic material.
The information from the genome can be
used to identify and diagnose inherited
disorders.
Biologists can now read, analyze, and
change the molecular code of genes.
Human DNA Analysis

Since the human genome is so large,
biologists can search a human genome
using DNA sequences by a process called
DNA testing

For example, if parents suspect they carry
recessive alleles for a recessive genetic
disorder, genetic testing can be performed to
spot any differences in the DNA sequence in a
specific disease causing allele.
Human DNA Analysis

Since no two individuals have the exact same genome,
biologist can use DNA fingerprinting to identify
individuals

For example, if blood, sperm or hair is found at a crime scene,
DNA from the tissue can be cut using restriction enzymes and
fragments can be separated using gel electrophoresis, resulting
in a unique pattern that can be compared to a suspect’s DNA
The Human Genome Project


The Human Genome
Project is an attempt to
sequence all human DNA.
In February 2001,
scientists successfully
mapped the human
genome
 If your genome were a
textbook, it would be 4
million pages long.
The Human Genome Project



Scientists are actively looking for genes that may
provide useful clues to some of the basic
properties of life.
Biotechnology companies are trying to find
genetic information that may be useful in
developing new drugs and treatments for
diseases.
The most amazing thing: The human genome
data is posted on the Internet!
http://www.ornl.gov/sci/techresources/Human_Genome/posters/chromosome/chooser.shtml
Gene Therapy


It would make sense to use this information to cure
genetic disorders
Gene therapy = an absent or faulty gene is replaced by
a normal, working gene, but it can’t be inherited unless
a reproductive cell is altered!
 Some researchers insert a DNA fragment containing a
replacement gene into viral DNA, and then infect the
patient with the modified virus, which should carry
the gene into cells and correct the genetic disorder.
Interest Grabber
Section 14-3
Bioethics and You
As
you become more aware of scientific advances in
genetics, you might realize that with the ability to
manipulate genes, there comes responsibility. This
ability provides an opportunity to improve the lives of
many people. But there is also a potential for errors or
intentional misuse of the technology.



Go to
Section:
Working with a partner, answer the following questions.
1. In what type of situation do you think genetic engineering—changing
the genes of organisms—is warranted? Explain your reasoning about
your position. If you do not think that genetic engineering is ever
warranted, explain your reasons for your position.
2. In what type of situation do you think genetic engineering might be
misused? Suggest limits that might be placed on the manipulation of
genes to avoid its misuse.
Stations Activity

Take one minute at each station to read
the description and discuss the questions.