A Family Tree

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A Family Tree
Section 14-1
Interest Grabber

• To 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.

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Section 14-1

• 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 childs
  spouse have attached ear lobes? Do any of this
  childs children have attached ear lobes?

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3
Section 14-1

• 141 Human Heredity
• A. Human Chromosomes
• B. Human Traits
• C. Human Genes
• 1. Blood Group Genes
• 2. Recessive Alleles
• 3. Dominant Alleles
• 4. Codominant Alleles
• D. From Gene to Molecule
• 1. Cystic Fibrosis
• 2. Sickle Cell Disease
• 3. Dominant or Recessive?

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4
KEY CONCEPT A combination of methods is used to
study human genetics.
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Human genetics follows the patterns seen in other
organisms.

• The basic principles of genetics are the same in
  all sexually reproducing organisms.
• Inheritance of many humantraits is complex.
• Single-gene traits areimportant in
  understandinghuman genetics.

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• Karyotype
• A set of photographs of chromosomes grouped in
  order in pairs.
• Sex chromosome
• One of two chromosomes that determine an
  individuals sex
• Autosome
• Not a sex chromosome

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Karyotype

• Several methods help map human chromosomes.

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Karyotypes can show changes in chromosomes.

• deletion of part of a chromosome or loss of a
  chromosome
• large changes in chromosomes
• extra chromosomes or duplication of part of a
  chromosome

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• Karyotype collection of chromosomes found in
  cell (photograph of duplicated chromosomes before
  mitosis)
• USE COUNT the number of chromosomes and see IF a
  trisomy or monosomy condition exists prior to the
  birth of the child

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• Pedigree
• Chart that shows the relationships in a family
• Polygenic
• Controlled by two or more genes.

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A pedigree is a chart for tracing genes in a
family.

• Phenotypes are used to infer genotypes on a
  pedigree.
• Autosomal genes show different patterns on a
  pedigree than sex-linked genes.

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What is a Pedigree?

• A pedigree is a chart of the genetic history of a
  family over several generations.
• Pedigrees used to determine the probability of a
  child having a disorder in a particular family.

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Figure 14-3 A Pedigree
Section 14-1
A square represents a male.
A circle represents a female.
A horizontal line connecting a male and female
represents a marriage.
A vertical line and a bracket connect the parents
to their children.
A half-shaded circle or square indicates that a
person is a carrier of the trait.
A circle or square that is not shaded indicates
that a person neither expresses the trait nor is
a carrier of the trait.
A completely shaded circle or square indicates
that a person expresses the trait.
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Connecting Pedigree Symbols
Examples of connected symbols

• Married Couple
• Siblings

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Connecting Pedigree Symbols
Examples of connected symbols

• Fraternal twins
• Identical twins

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Interpreting Pedigrees

• Determine if the pedigree chart shows an
  autosomal or X-linked disease.
• If most males affected, likely X-linked
• If 50/50 ratio male/female, likely autosomal.

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Example of Pedigree Charts

• Is it Autosomal or X-linked?

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Interpreting a Pedigree Chart

• Determine if disorder dominant or recessive.
• If the disorder is dominant, one of the parents
  must have the disorder.
• If the disorder is recessive, neither parent has
  to have the disorder because they can be
  heterozygous.

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Example of Pedigree Charts

• Dominant or Recessive?

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KEY CONCEPT The chromosomes on which genes are
located can affect the expression of traits.
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Two copies of each autosomal gene affect
phenotype.

• Mendel studied autosomal gene traits, like hair
  texture.

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• Mendels rules of inheritance apply to autosomal
  genetic disorders.

• A heterozygote for a recessive disorder is a
  carrier.
• Disorders caused by dominant alleles are uncommon.

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• MUTATION change in the DNA which MAY affect a
  gene or chromosome
• Causes of mutations
• 1) DNA transcription/translation errors
• 2) Chemical or carcinogen mutagens
• Mutations in our DNA (gene mutations especially)
  can
• result in an abnormality.
• IF the mutation occurs in a BODY CELL (Ex skin
  cell) - may or may not be harmful you can not
  pass this on to your children

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• IF the mutation occurs in one of your gametes
  (egg or sperm) - future generations can be
  affected
• Mutations are changes in DNA
• Mutated genes can lead to many genetic disorders
• Many mutations that cause these disorders are
  carried as a sex linked GENE in a normal or
  carrier individual

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• Human Chromosomal Disorders
• Chromosomes Affect Development 46 chromosomes
  must be present for normal development! A Car
  needs all its parts to function
• Monosomy- diploid cell is missing a chromosome
• (embryo dies) A Car without major parts will not
  run
• Trisomy- diploid cell has an extra chromosome
• Ex Trisomy 21 Down Syndrome

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Number of Cases of Down Syndrome
Number/1000 Births Maternal Age Group
0.6 20-24
0.8 25-29
1.5 30-34
2.6 35-39
14.3 40-44
34.2 45
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• Why?
• Eggs accumulate increasing damage throughout
  life.
• Males produce new sperm throughout life.
• How does cell get extra chromosome?
• Accident during Meiosis when cell divides
  normally,
• the chromosome and its homologue (chromatids)
  separate.
• Nondisjunction chromosomes which fail to
  separate
• normally (one cell gets an extra chromosome and
  the other cell loses a chromosome)

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Section 14-2
Nondisjunction
Homologous chromosomes fail to separate
Meiosis I Nondisjunction
Meiosis II
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• SICKLE CELL ANEMIA is an example of a recessive
  disorder of the RED BLOOD
• CELLS - GENE codes for a defective form of the
  protein, Hemoglobin (oxygen-carrying molecule in
  the red blood cell)
• IF low oxygen condition or acidic condition, red
  blood cells
• become sickle shaped.
• They DO NOT carry oxygen very well AND cells DO
  NOT move
• very well through blood vessels clump up and
  can cut off the blood supply to different organs

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Common in West Africa - small percent of African
Americans Punnett Square for Sickle Cell Anemia
IF each parent carries a copy of the sickle cell
gene S normal red blood cell gene s sickle
cell gene
S s
S SS Ss
s Ss ss
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Sickle cell anemia WHAT advantage could there be
to being HETERZYGOUS for the sickle cell gene?
Disease ADVANTAGE In areas of Central Africa,
the blood cells infected by the parasite from a
mosquito's bite will sickle and be destroyed by
the body (ALSO destroying the parasite!!!)
Plasmodium MALARIA
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Concept Map
Section 14-1
Autosomol Disorders
caused by
include
include
include
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Figure 14-8 The Cause of Cystic Fibrosis
Section 14-1
Chromosome 7
CFTR gene
The most common allele that causes cystic
fibrosis is missing 3 DNA bases. As a result,
the amino acid phenylalanine is missing from the
CFTR protein.
Normal CFTR is a chloride ion channel in cell
membranes. Abnormal CFTR cannot be transported
to the cell membrane.
The cells in the persons airways are unable to
transport chloride ions. As a result, the airways
become clogged with a thick mucus.
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Gender Benders
Section 14-2
Interest Grabber

• 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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Section 14-2

• 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?

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36
Section 14-2

• 142 Human Chromosomes
• A. Human Genes and Chromosomes
• B. Sex-Linked Genes
• 1. Colorblindness
• 2. Hemophilia
• 3. Duchenne Muscular Dystrophy
• C. X-Chromosome Inactivation
• D. Chromosomal Disorders
• 1. Down Syndrome
• 2. Sex Chromosome Disorders

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37

• Sex-Linked Gene
• Gene located on the X or Y chromosome
• Nondisjunction
• Error in meiosis in which homologous chromosomes
  fail to separate

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Males and females can differ in sex-linked
traits.

• Genes on sex chromosomes are called sex-linked
  genes.
• Y chromosome genes in mammals are responsible for
  male characteristics.
• X chromosome genes in mammals affect many traits.

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• Male mammals have an XY genotype.

• All of a males sex-linked genes are expressed.
• Males have no second copies of sex-linked genes.

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Females can carry sex-linked genetic disorders.

• Males (XY) express all of their sex linked genes.
• Expression of the disorder depends on which
  parent carries the allele and the sex of the
  child.

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Sex Linked Disorders

• Sex-linked Disorders
• These are disorders tied to genes located on the
  sex chromosomes - X or Y
• Sex-linked disorders in Humans
• 1) Color Blindness -cannot tell the difference
• between red and green (1 in 10 males in U.S.)
• Caused by defective allele on the X chromosome

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• Mostly males are color blind
• WHY?
• Males have only one X chromosome- defective
• gene will be expressed even IF RECESSIVE
• Female needs two defective X chromosomes to
• be color blind (1 in 100 in U.S.)
• Females with ONLY ONE defective X chromosome are
• carriers of color blindness but have normal
  vision.

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Section 14-2
Figure 14-13 Colorblindness
Normal vision
Colorblind
Father (normal vision)
Male Female
Daughter (normal vision)
Son (normal vision)
Mother (carrier)
Son (colorblind)
Daughter (carrier)
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• 2) What are the CHANCES of passing a trait onto
  your children?
• HOW is a pedigree determined?
• Study family histories and find out who has a
  trait.
• DISCOVER
• Dominant traits
• Recessive traits
• Sex-linked traits (genes only on sex
  chromosomes)
• Autosomal traits (genes NOT on a sex chromosome)

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• SAMPLE PEDIGREE
• Albinism genetic disorder in which a defective
  gene does not allow a cell to produce pigment
  (color) Skin and hair are white
• 1st QUESTION Is this trait SEX-LINKED or NOT?
• IF ONLY found in males, usually sex-linked (only
  have one X chromosome)
• IF found in both male and female, probably not
  sex-linked

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• ALBINISM? 3 males, 2 females
• autosomal
• 2nd QUESTION Is trait DOMINANT or RECESSIVE?
• If dominant, every individual with albinism will
  have
• IF recessive, can have heterozygous parents who
  appear normal!
• ALBINISM Is Recessive
• 3rd QUESTION Is this disorder controlled by ONE
  gene or multiple
• genes?
• IF single recessive gene, then parents can
  expect to
• produce affected children in a 31 ratio of
  normal-to-albino children
• (25)
• IF more than one gene, percentage will be even
  LOWER
• ALBINISM 517 or 29

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Section 14-3

• 14-3 Human Molecular Genetics
• A. Human DNA Analysis
• 1. Testing for Alleles
• 2. DNA Fingerprinting

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• Testing for Alleles
• Alleles responsible for genetic disorders have a
  different DNA sequences than the normal
  counterpart.
• Genetic testing Genetic tests have been
  developed to spot the defective sequence. Other
  tests detect changes in restriction enzyme
  cutting sites or differences in lengths of normal
  and abnormal alleles.
• Prenatal Testing
• Amniocentesis sample of fluid surrounding the
  fetus is taken with a long, thin needle Cells
  from the fluid can be grown in culture and
  karyotype prepared

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Diagnosis of Genetic disorders

• Finding differences between those who have the
  disorder, and those who dont
• Gel electrophoresis, differences in bands

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Gene Therapy

• Insertion of normal genes into human cells to
  correct genetic disorders
• Still experimental
• Ex) SCID (severe combined immunodeficiency
  syndrome) immune system is shut down
• -functional genes inserted into bone marrow

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Stem Cell

• Undifferentiated cells, capacity to develop into
  any type of cell
• Repair tissue or grow organs
• Problems mastering signals, replicating,
  staying for life?

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• DNA Fingerprinting
• Analysis of sections of DNA that have no known
  function but vary widely in individuals, used for
  identification.

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DNA fingerprinting

• Gel electrophoresis, creates distinct bands
• Used in law-enforcement
• Question? A girl is interviewed as a possible
  suspect in a crime. She claims that her twin
  sister committed it, is this possible?

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Section 14-3
Figure 14-18 DNA Fingerprinting
Restriction enzyme
Chromosomes contain large amounts of DNA called
repeats that do not code for proteins. This DNA
varies from person to person. Here, one sample
has 12 repeats between genes A and B, while the
second sample has 9 repeats.
Restriction enzymes are used to cut the DNA into
fragments containing genes and repeats. Note that
the repeat fragments from these two samples are
of different lengths.
The DNA fragments are separated according to size
using gel electrophoresis. The fragments
containing repeats are then labeled using
radioactive probes. This produces a series of
bandsthe DNA fingerprint.
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