Transcript Pre – AP Biology

AP Biology
Mendelian Genetics
Part 4
• Important concepts from previous units:
• Genes are located on chromosomes.
• There are two types chromosomes associated
humans – autosomes and sex chromosomes.
• Chromosomes are inherited from the parents.
One from EACH parent
Sperm AND Egg
Genes on Chromosomes
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Linked Genes
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These are usually inherited as a linked unit
because they are found on the same
chromosome.
This term usually is associated with genes on
Autosomes (1-22).
Autosomes and linked genes
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Alfred Sturtevant
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He was the pioneer of genetic mapping –
locating the loci of genes.
He used crossover rates to determine the loci
on chromosomes.
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The finished product is called a Linkage Map.
The smaller the rate; the closer they are to each
other on the same chromosome.
The higher the rate; the farther apart they are from
each other on the same chromosome.
The loci are measured in Centimorgans or map
units.
Linkage Map based
on Crossover
frequency
Recombination
frequencies
9%
9.5%
17%
b
Chromosome
cn
vg
Locus Gene Maps
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Sex-Linked Genes
– This term refers to genes found on the sex
chromosomes; 95% of the time it mainly
refers to the X chromosome. (Think X when
it is seX linked.)
• This is because both sexes have at least
one X chromosome in their genome.
• XX (Female and homologous) ; XY (Male
and heterologous)
– Sex chromosomes undergo very little
crossover during Prophase I of Meiosis.
Sex –Linked Female – TWO Xs
Sex-Linked Male – ONE X
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Sex of the organism will be determined at
conception. This is when egg is fertilized by the
sperm. You will either get a sperm containing an X
chromosome or a sperm containing a Y
chromosome.
Everyone starts out female. (This is why we all have
nipples.)
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At about two months of age in the womb, the Y
chromosome’s SRY gene goes active to make
testosterone, from estrogen, to finish development
of the male. (Remember, functional groups.)
After development is complete, testosterone
production is turned off until puberty. At puberty it is
turned back on so as to make the secondary sexual
characteristics, such as facial hair.
Patterns of Inheritance and some Human Sex-Linked
Genetic Disorders: (NO cure exists, because the problem
is in the DNA.)
• Color Blindness
– This is the result of a faulty gene
(recessive) on the X chromosome for
making a particular type of light
wavelength (color) absorbing protein in
cones of the retina of the eye.
– The most common type is Red/Green
Colorblindness. (Red and Green appear
gray.)
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Hemophilia (Means “love of bleeding”)
– These individuals CANNOT make (recessive) Antihemolytic Factor. (AHF for short.)
– They may experience problems with possible
bleeding to death.
– This was a disorder associated with the “Royal BlueBloods of Europe” – They were inbreeding to keep
the crown “In the Family”.
– Treatment? These individuals have to keep AHF with
them at all times in case they get hurt. If they do get
hurt and start to bleed, they will require a shot of
AHF to stop the bleeding. Even a bruise (bleeding
under the skin) can possibly lead to death.
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THE PATTERN ON A PEDIGREE: It will appear to
mainly affect males (as they only have one X
chromosome). This is because if the inherited X
chromosome has a recessive gene on it; it will NOT
be covered up by a dominant one on another X
chromosome (as is the case in most females).
Females can still get these disorders, but they must
inherit two recessive X chromosomes. The females
tend to be carriers, so they appear unaffected. So
they tend to pass the recessive X on to their sons.
The son will be a sufferer, if he gets the recessive X,
of the disorder. It appears to skip a generation,
because the mother is a carrier and the sons are
showing the disorder.
Pedigree of Color Blindness
Pedigree of Hemophila
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Genes associated with these two terms
(linked genes and sex-linked genes) do not
follow Mendel’s Laws of Inheritance and
normal ratios.
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This is because these terms are mostly
referencing one chromosome and not inherited
pairs of chromosomes.
Variation on linked chromosomes is associated
with crossover frequency with its homologous
mate.
Sex –linked is referencing the X chromosome
only. Males have 1 and females two copies.
AP Biology
Mendelian Genetics
Part 5
• Important concepts from previous units:
• There are also gene errors – point mutations
and reading frame mutations.
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Chromosomal Errors than can occur:
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These could occur during Mitosis or Meiosis.
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They would occur during the Anaphase Stages
where chromosomes are moving.
They could also occur during Crossover where gene
DNA segments are moving.
Non-Disjunction
Down syndrome
• Trisomy 21, because the person has three
copies of chromosome 21 instead of two
• Some of the characteristics of may include:
– outwardly slanted eyes
– exaggerated fold of skin on the inside of the eye
– flat ears set low on the head
– flattened face
– small teeth
– relatively short arms and legs.
Edward syndrome
• Trisomy 18, because the person has three copies of
chromosome 18
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Some of the characteristics of Edward syndrome may include:
defects of the kidneys, ureters, heart, lungs and diaphragm
cleft lip or cleft palate
small skull (microcephaly)
malformations of the hands and feet – including missing
thumbs, club feet and webbing between the fingers and toes
(syndactyly)
– neural tube defect, where the spinal cord, meninges and blood
vessels protrude through a gap in the vertebrae
(myelomeningocele)
– malformations of the sex organs
– survival beyond the neonatal period is uncommon.
Patau Syndrome
• Trisomy 13, because the person has three copies of chromosome 13
instead of two.
• Some of the characteristics of Patau syndrome may include:
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small skull (microcephaly)
an abnormal opening in the skull
malformations of part of the brain
structural defects of the eyes
cleft lip or cleft palate
additional toes or fingers (polydactyly)
congenital heart disorders, such as ventricular septal defect
neural tube defect, where the spinal cord, meninges and blood vessels
protrude through a gap in the vertebrae (myelomeningocele)
– malformations of the sex organs
– survival beyond the neonatal period is uncommon.
Triple X syndrome (XXX)
• may be taller than average
• Most females with triple X syndrome have normal
sexual development and are able to conceive children.
• Triple X syndrome is associated with an increased risk
of learning disabilities and delayed development of
speech and language skills. Delayed development of
motor skills (such as sitting and walking), weak muscle
tone (hypotonia), and behavioral and emotional
difficulties are also possible, but these characteristics
vary widely among affected girls and women. Seizures
or kidney abnormalities occur in about 10 percent of
affected females.
XYY
• may be taller than average
• Most males with 47,XYY syndrome have normal sexual
development and are able to father children.
• XYY syndrome is associated with an increased risk of learning
disabilities and delayed development of speech and language skills.
Delayed development of motor skills (such as sitting and walking),
weak muscle tone (hypotonia), hand tremors or other involuntary
movements (motor tics), and behavioral and emotional difficulties
are also possible
• A small percentage of males with 47,XYY syndrome are diagnosed
with autistic spectrum disorders which are developmental
conditions that affect communication and social interaction
Klinefelter (XXY)
• Extra copies of genes on the X chromosome interfere with male
sexual development, often preventing the testes from functioning
normally and reducing the levels of testosterone.
• A shortage of testosterone can lead to delayed or incomplete
puberty, breast enlargement (gynecomastia), reduced facial and
body hair, and an inability to have biological children (infertility)
• Children with Klinefelter syndrome may have learning disabilities
and delayed speech and language development. They tend to be
quiet, sensitive, and unassertive, but personality characteristics
vary among affected individuals.
• Older children and adults with Klinefelter syndrome tend to be
taller than their peers. Compared with unaffected men, adults with
Klinefelter syndrome have an increased risk of developing breast
cancer
Turner (XO)
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monosomy X, which means each cell in the individual's body has only one copy of the X
chromosome
the most common feature of Turner syndrome is short stature, which becomes evident by
about age 5.
An early loss of ovarian function (ovarian hypofunction or premature ovarian failure) is also
very common.
About 30 percent of females with Turner syndrome have extra folds of skin on the neck
(webbed neck), a low hairline at the back of the neck, puffiness or swelling (lymphedema) of
the hands and feet, skeletal abnormalities, or kidney problems.
One third to one half of individuals with Turner syndrome are born with a heart defect, such as
a narrowing of the large artery leaving the heart (coarctation of the aorta) or abnormalities of
the valve that connects the aorta with the heart (the aortic valve). Complications associated
with these heart defects can be life-threatening.
Most girls and women with Turner syndrome have normal intelligence. Developmental delays,
nonverbal learning disabilities, and behavioral problems are possible, although these
characteristics vary among affected individuals.
– Two types of errors can occur:
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Chromosomal Number (Aneuploidy means
“Abnormal number of chromosomes”)
– This is the result of non-disjunction. “Failure to separate”
during Anaphase.
– Trisomic - Three of 1 kind of chromosome.)
– Monosomic - Missing one, the other half of the pair. (It is
located in the Trisomic gamete.)
– Polyploidy - Many extra sets of chromosomes.
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i. 3n (triploid) - Three “halves” are in this
cell.
ii. 4n (tetraploid) - Four “halves” are in this
cell.
iii. Deadly in most animals; Plants not really
affected because they are simple organisms.
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Individual Chromosome Structure
» These occur because of faulty crossover
» Deletion – Chromosome segment is “missing”. It got stuck on
the other homologous chromosome during crossover.
» Duplication – A chromosome segment was “copied” twice.
Two genes on one chromosome. It is “missing” from the
other homologous chromosome.
» Inversion – A chromosomal segment is “backwards”. It was
inverted (“backwards”) during crossover.
» Translocation – A chromosomal segment is attached to a
different autosome. It accidentally broke loose and ended up
on another chromosome.
Cri-du-chat
• Cri-du-chat (cat's cry) syndrome, also known as 5p- (5p
minus) syndrome, is a chromosomal condition that
results when a piece of chromosome 5 is missing. Infants
with this condition often have a high-pitched cry that
sounds like that of a cat. The disorder is characterized by
intellectual disability and delayed development, small
head size (microcephaly), low birth weight, and weak
muscle tone (hypotonia) in infancy. Affected individuals
also have distinctive facial features, including widely set
eyes (hypertelorism), low-set ears, a small jaw, and a
rounded face. Some children with cri-du-chat syndrome
are born with a heart defect.
Chromosome Structure Errors
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Syndrome
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This term refers to an organism “possessing”
the identifying traits of a particular genetic
disorder.
Human Genetic Disorders due to two abnormal
chromosomal number:
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Down’s Syndrome
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This affects about 1 in 700 births.
This individuals possess an extra 21 Autosome (A.K.A.
Trisomy 21)
General syndrome features – mental retardation, flat
face, squinted eyes, small.
Mainly the result of women of advanced age having
babies.
Trisomy 21
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Extranuclear DNA (“extra” means “outside of”)
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DNA that is located outside the nucleus in organelles.
(These are Mitochondria, Chloroplasts, and Plastids.)
Mitochondria inherited from the mother inside the egg.
They are exactly alike. (Helps in Criminal Forensics
cases trying to establish relationship between
individuals.)
Mitochondrial Myopathy - These mitochondria lack
the ability to make large quantities of ATP because they
posses faulty DNA for making some of the enzymes or
proton pump proteins in the cellular respiration
process.)
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General Characteristics: These individuals are very tired all the
time.
Extranuclear DNA
(This DNA CAN can affect an organism)