Human GeneticsHuman
Genetics
Chapter 15: The Chromosomal Basis of Inheritance
Genes & ChromosomesGenes & Chromosomes
Mendel’s “hereditary factors” were , though this wasn’t known at the time
Today we can show that genes are
The location of a particular gene can be seen by tagging isolated chromosomes with
Mendel’s “hereditary factors” were , though this wasn’t known at the time
Today we can show that genes are
The location of a particular gene can be seen by tagging isolated chromosomes with
Chromosomal Theory of Inheritance
Chromosomal Theory of Inheritance
Mitosis and meiosis were first described in the
The chromosome theory of inheritance states:
The behavior of chromosomes during meiosis was said to account for Mendel’s laws of segregation and independent assortment
Mitosis and meiosis were first described in the
The chromosome theory of inheritance states:
The behavior of chromosomes during meiosis was said to account for Mendel’s laws of segregation and independent assortment
Experimental EvidenceExperimental EvidenceThe first solid evidence
associating a specific gene with a specific chromosome came from
Morgan’s experiments with fruit flies provided convincing evidence that
The first solid evidence associating a specific gene with a specific chromosome came from
Morgan’s experiments with fruit flies provided convincing evidence that
Experimental EvidenceExperimental EvidenceIn one experiment, Morgan
mated male flies with white eyes (mutant) with female flies with red eyes (wild type or normal)The F1 generation
The F2 generation showed the 3:1 red:white eye ratio, but
Morgan determined that the white-eyed mutant allele must be located
Morgan’s finding supported the
In one experiment, Morgan mated male flies with white eyes (mutant) with female flies with red eyes (wild type or normal)The F1 generation
The F2 generation showed the 3:1 red:white eye ratio, but
Morgan determined that the white-eyed mutant allele must be located
Morgan’s finding supported the
Sex linkageSex linkageSex chromosomes
determine XX in females, XY in
malesEach ovum contains an
, while a sperm may contain
The SRY gene on the Y chromosome codes for the
X chromosome has genes for many traits
Sex chromosomes determine XX in females, XY in
malesEach ovum contains an
, while a sperm may contain
The SRY gene on the Y chromosome codes for the
X chromosome has genes for many traits
Sex-linked InheritanceSex-linked InheritanceA gene located on either
sex chromosome is called a
In humans, sex-linked usually refers to a gene on the
If gene is on Sons will inherit from Females don’t get Y-
linked traitsY-linked genes
A gene located on either sex chromosome is called a
In humans, sex-linked usually refers to a gene on the
If gene is on Sons will inherit from Females don’t get Y-
linked traitsY-linked genes
X-linked InheritanceX-linked Inheritance
If gene is on
Can inherit from
Sons always get
If gene is on
Can inherit from
Sons always get
X-linked traitsX-linked traits
AKA Bubble boy disease
AKA Bubble boy disease
X-linked recessive genes
X-linked recessive genes
Sex-linked genes follow specific patterns of inheritance
For a recessive sex-linked trait to be expressedA female
A male
Sex-linked recessive disorders are much
Sex-linked genes follow specific patterns of inheritance
For a recessive sex-linked trait to be expressedA female
A male
Sex-linked recessive disorders are much
Females & X-linkedFemales & X-linked
In mammalian females, one of the two X chromosomes in each cell is
The inactive X condenses
into a If a female is heterozygous
for a particular gene located on the X chromosome, she will be a
In mammalian females, one of the two X chromosomes in each cell is
The inactive X condenses
into a If a female is heterozygous
for a particular gene located on the X chromosome, she will be a
CarriersCarriersFemales can be
Have one copy of gene,
Other X has
Males cannot be carriers, they either Males will give gene to
If he has the gene all his daughters will be
Females can be Have one copy of gene,
Other X has
Males cannot be carriers, they either Males will give gene to
If he has the gene all his daughters will be
Red-green color blindness
Red-green color blindness
X-linked disorderCan’t differentiate these two
colorsMany people who have this are
First described in a boy who could not be trained to harvest only the ripe, red apples from his father’s orchard.
What serious consequence could result from this?
X-linked disorderCan’t differentiate these two
colorsMany people who have this are
First described in a boy who could not be trained to harvest only the ripe, red apples from his father’s orchard.
What serious consequence could result from this?
Sex-Linked Traits:
1. Normal Color Vision: A: 29, B: 45, C: --, D: 26
2. Red-Green Color-Blind: A: 70, B: --, C: 5, D: --
3. Red Color-blind: A: 70, B: --, C: 5, D: 6
4. Green Color-Blind: A: 70, B: --, C: 5, D: 2
HemophiliaHemophiliaAn X-linked disorder
that causes a
If your blood didn’t have the ability to clot and you bruised yourself or scraped your knee,
Queen Victoria was a carrier and she passed the trait on to some of her children
An X-linked disorder that causes a
If your blood didn’t have the ability to clot and you bruised yourself or scraped your knee,
Queen Victoria was a carrier and she passed the trait on to some of her children
HemophiliaHemophilia
About has hemophilia, but only about inherits the same disorder
Why????Males only have
A single recessive allele for hemophilia will
Females would need to inherit hemophilia
Males inherit the allele for hemophilia on the X chromosome from their
About has hemophilia, but only about inherits the same disorder
Why????Males only have
A single recessive allele for hemophilia will
Females would need to inherit hemophilia
Males inherit the allele for hemophilia on the X chromosome from their
HemophiliaHemophilia
HemophiliaHemophiliaHemophilia can be treated
with , the
blood-clotting enzyme that is absent in people affected by the condition
Both treatments are New methods of DNA
technology are being used to develop a
Hemophilia can be treated with
, the blood-clotting enzyme that is absent in people affected by the condition
Both treatments are New methods of DNA
technology are being used to develop a
Sex-linked QuestionsSex-linked Questions Both the mother and the father of a male
hemophiliac appear normal. From whom did the son inherit the allele for hemophilia? What are the genotypes of the mother, the father and the son?
A woman is color blind. If she marries a man with normal vision, what are the chances that her daughter will be color blind? Will be carriers? What are her chances that her sons will be color blind?
Is it possible for two normal parents to have a color blind daughter?
Both the mother and the father of a male hemophiliac appear normal. From whom did the son inherit the allele for hemophilia? What are the genotypes of the mother, the father and the son?
A woman is color blind. If she marries a man with normal vision, what are the chances that her daughter will be color blind? Will be carriers? What are her chances that her sons will be color blind?
Is it possible for two normal parents to have a color blind daughter?
What is on our chromosomes?What is on our chromosomes?
Each chromosome has Genes located on the same chromosome that
tend to be inherited together are called Thomas Morgan found that body color and wing
size of fruit flies are usually inherited together in
He noted that these genes do not , and reasoned that they were
However, nonparental phenotypes were also produced
Understanding this result involves exploring
Each chromosome has Genes located on the same chromosome that
tend to be inherited together are called Thomas Morgan found that body color and wing
size of fruit flies are usually inherited together in
He noted that these genes do not , and reasoned that they were
However, nonparental phenotypes were also produced
Understanding this result involves exploring
Genetic RecombinationGenetic Recombination
Mendel observed that combinations of traits in some offspring differ from either parent
Offspring with a phenotype matching one of the parental phenotypes are called
Offspring with nonparental phenotypes (new combinations of traits) are called
Morgan discovered that genes can be linked, but the linkage was Morgan proposed that some process must
sometimes break the physical connection between genes on the same chromosome
Mechanism was the
Mendel observed that combinations of traits in some offspring differ from either parent
Offspring with a phenotype matching one of the parental phenotypes are called
Offspring with nonparental phenotypes (new combinations of traits) are called
Morgan discovered that genes can be linked, but the linkage was Morgan proposed that some process must
sometimes break the physical connection between genes on the same chromosome
Mechanism was the
Genetic mapGenetic map
Alfred Sturtevant, one of Morgan’s students, constructed a
Sturtevant predicted that the farther apart two genes are, the
and therefore the higher the recombination frequency
Alfred Sturtevant, one of Morgan’s students, constructed a
Sturtevant predicted that the farther apart two genes are, the
and therefore the higher the recombination frequency
Genetic mapGenetic mapA linkage map is a genetic map of a chromosome
based on Distances between genes can be expressed as
; one map unit, or centimorgan, represents a
Map units indicate , not precise locations of genes
A linkage map is a genetic map of a chromosome based on
Distances between genes can be expressed as ; one map unit, or centimorgan, represents a
Map units indicate , not precise locations of genes
Human Genome Project
Human Genome Project
The most ambitious mapping project to date has been the sequencing of the
Officially begun as the Human Genome Project in , the sequencing was largely completed by
The project had three stages:
The most ambitious mapping project to date has been the sequencing of the
Officially begun as the Human Genome Project in , the sequencing was largely completed by
The project had three stages:
Human Genome Project
Human Genome Project
A physical map expresses the distance between genetic markers,
It is constructed by cutting a DNA molecule into many short fragments and arranging them in order by identifying overlaps
Sequencing was then done on the chromosomes
A physical map expresses the distance between genetic markers,
It is constructed by cutting a DNA molecule into many short fragments and arranging them in order by identifying overlaps
Sequencing was then done on the chromosomes
Gene ManipulationGene ManipulationDNA sequencing has
depended on advances in technology, starting with making recombinant DNA
In recombinant DNA, nucleotide sequences from
Methods for making recombinant DNA are central to genetic engineering,
DNA sequencing has depended on advances in technology, starting with making recombinant DNA
In recombinant DNA, nucleotide sequences from
Methods for making recombinant DNA are central to genetic engineering,
BiotechnologyBiotechnology
DNA technology has revolutionized biotechnology,
One benefit of DNA technology is identification of human genes in which
Scientists can diagnose many human genetic disorders by using molecular biology techniques to
Genetic disorders can also be tested for using
DNA technology has revolutionized biotechnology,
One benefit of DNA technology is identification of human genes in which
Scientists can diagnose many human genetic disorders by using molecular biology techniques to
Genetic disorders can also be tested for using
TransgenicsTransgenicsAdvances in DNA technology and genetic
research are important to the development of
Transgenic animals are made by introducing genes from Transgenic animals are pharmaceutical “
,” producers of large amounts of otherwise rare substances for medical use
“Pharm” plants are also being developed to make human proteins for medical use
This is useful for the production of
Advances in DNA technology and genetic research are important to the development of
Transgenic animals are made by introducing genes from Transgenic animals are pharmaceutical “
,” producers of large amounts of otherwise rare substances for medical use
“Pharm” plants are also being developed to make human proteins for medical use
This is useful for the production of
Gene TherapyGene Therapy
Gene therapy is the alteration of an
Gene therapy holds great potential for treating
Vectors are used for
(example = bone marrow)Gene therapy raises ethical
questions, such as whether human germ-line cells should be treated to correct the defect in future generations
Gene therapy is the alteration of an
Gene therapy holds great potential for treating
Vectors are used for
(example = bone marrow)Gene therapy raises ethical
questions, such as whether human germ-line cells should be treated to correct the defect in future generations
Causes of Genetic Disorders
Causes of Genetic Disorders
Meiosis usually functions accurately, but problems may arise at times
Large-scale chromosomal alterations often lead to
In nondisjunction, pairs of homologous chromosomes May occur in One gamete receives
Another gamete receives
Meiosis usually functions accurately, but problems may arise at times
Large-scale chromosomal alterations often lead to
In nondisjunction, pairs of homologous chromosomes May occur in One gamete receives
Another gamete receives
Fertilization after nondisjunction
Fertilization after nondisjunction
Nondisjunction results in gametes with an extra or missing chromosome
If the other gamete is normal, the zygote will have
Most of the time an extra chromosome
results from the fertilization of gametes in which nondisjunction occurred
Offspring with this condition have an
Nondisjunction results in gametes with an extra or missing chromosome
If the other gamete is normal, the zygote will have
Most of the time an extra chromosome
results from the fertilization of gametes in which nondisjunction occurred
Offspring with this condition have an
Fertilization after nondisjunction
Fertilization after nondisjunction
occurs when the zygote has only one copy of a particular chromosome (2n -1)
occurs when the zygote has three copies of a particular chromosome (2n+1)
is a condition in which an organism has more than two complete sets of chromosomes is three sets of chromosomes is four sets of chromosomes
Polyploidy is common in Polyploids are in appearance than
aneuploids
occurs when the zygote has only one copy of a particular chromosome (2n -1)
occurs when the zygote has three copies of a particular chromosome (2n+1)
is a condition in which an organism has more than two complete sets of chromosomes is three sets of chromosomes is four sets of chromosomes
Polyploidy is common in Polyploids are in appearance than
aneuploids
Nondisjunction animationAnimation #2
Human Disorders due to chromosome alterationsHuman Disorders due to chromosome alterations
are associated with some serious disorders
Some types of aneuploidy appear to upset the genetic balance less than others, resulting in
These surviving individuals have a set of symptoms,
are associated with some serious disorders
Some types of aneuploidy appear to upset the genetic balance less than others, resulting in
These surviving individuals have a set of symptoms,
Down SyndromeDown SyndromeDown syndrome is an
aneuploid condition that results from
Most common serious birth defect
Varying degrees of
Due to on 21st chromosome
1/2 eggs of female will carry extra 21 and 1/2 will be normal
Risk increases
Down syndrome is an aneuploid condition that results from
Most common serious birth defect
Varying degrees of
Due to on 21st chromosome
1/2 eggs of female will carry extra 21 and 1/2 will be normal
Risk increases
Incidence of Down Syndrome
Incidence of Down Syndrome
Klinefelter SyndromeKlinefelter Syndrome
Klinefelter syndrome is the result of an
Could be from
nondisjunction
Klinefelter syndrome is the result of an
Could be from
nondisjunction
Turner SyndromeTurner Syndrome
Turner syndrome produces
It is the only known
viable monosomy in humans
Girls with Turner Syndrome do not develop
Turner syndrome produces
It is the only known
viable monosomy in humans
Girls with Turner Syndrome do not develop
Mutation typesMutation types may
also lead to genetic disordersBreakage of a chromosome can lead to
four types of changes in chromosome structure:Deletion Duplication
Inversion
Translocation
may also lead to genetic disorders
Breakage of a chromosome can lead to four types of changes in chromosome structure:Deletion Duplication
Inversion
Translocation
Mutation typesMutation types
Cri du chatCri du chat
The syndrome cri du chat (“cry of the cat”), results from a
A child born with this syndrome is
Individuals usually die
The syndrome cri du chat (“cry of the cat”), results from a
A child born with this syndrome is
Individuals usually die
Chronic Myelogenous Leukemia
Chronic Myelogenous Leukemia
Certain cancers, including chronic myelogenous leukemia (CML), are caused by
Occurs with the exchange of a large portion of with a small
fragment from the tip of Shortened, easily recognizable
Certain cancers, including chronic myelogenous leukemia (CML), are caused by
Occurs with the exchange of a large portion of with a small
fragment from the tip of Shortened, easily recognizable
Genomic imprintingGenomic imprintingThere are two normal exceptions to Mendelian
geneticsOne exception involves , and
the other exception involves
Genes marked in gametes as coming from Genes inherited from father
than genes inherited from motherFor a small fraction of mammalian traits, the
for those traitsSuch variation in phenotype is called genomic
imprintingExample =
There are two normal exceptions to Mendelian genetics
One exception involves , and the other exception involves
Genes marked in gametes as coming from Genes inherited from father
than genes inherited from motherFor a small fraction of mammalian traits, the
for those traitsSuch variation in phenotype is called genomic
imprintingExample =
Organelle genes Organelle genes Extranuclear genes (or
cytoplasmic genes) are genes found
Mitochondria, chloroplasts, and other plant plastids carry
Extranuclear genes are inherited
Extranuclear genes (or cytoplasmic genes) are genes found
Mitochondria, chloroplasts, and other plant plastids carry
Extranuclear genes are inherited
Organelle genes Organelle genes The first evidence of
extranuclear genes came from studies on the inheritance of yellow or white patches on leaves of an otherwise green plant
Some defects in mitochondrial genes prevent cells from making enough ATP and result in
For example,
mitochondrial myopathy and Leber’s hereditary optic neuropathy
The first evidence of extranuclear genes came from studies on the inheritance of yellow or white patches on leaves of an otherwise green plant
Some defects in mitochondrial genes prevent cells from making enough ATP and result in
For example,
mitochondrial myopathy and Leber’s hereditary optic neuropathy
Review QuestionsReview Questions1. State the 2 basic ideas behind the chromosomal theory of
inheritance.2. Explain Morgan’s experiment and how it gave evidence that
genes are located on chromosomes.3. Explain sex linkage and sex-linked inheritance.4. Name and describe characteristics of 4 genetic diseases
that are known to be X-linked.5. Explain the idea of a “carrier” for an X-linked genetic
disease.6. Carry out a monohybrid cross of an X-linked trait using a
Punnett square.7. Explain the idea of linked genes.8. Explain the result of genetic recombination.9. Identify the significance of genetic maps and linkage maps10. Describe the Human Genome Project and differentiate
between its 3 main stages.11. Discuss the advantages of gene manipulation and
biotechnology.12. Describe various uses of transgenic animals.13. Explain the purpose and use of gene therapy.14. Explain how errors in meiosis can cause genetic syndromes.
Review QuestionsReview Questions15. Define nondisjunction.16. Differentiate between aneuploidy, monosomy, trisomy, and
polyploidy.17. Explain the cause, frequency, and problems associated with
the following genetic syndromes: Down syndrome, Klinefelter syndrome, & Turner syndrome.
18. Describe the effect of mutations on genes.19. Differentiate between deletion, duplication, inversion, and
translocation mutations.20. Explain cri du chat syndrome.21. Explain chronic myelogenous leukemia as an example of a
disease-causing mutation.22. Explain genomic imprinting and the effects of extranuclear
genes.