Download Chromosomes and Inertitance

5-17 ATB
 What are chromosomes composed of?
Where do we find chromosomes?
 Objectives:
 Discuss sex-linked traits
Chromosomes and
Inheritance
Chapter 12
Review:
•Sex chromosomes –
•chromosomes that contain genes that
determine sex (along with other traits)
•Autosomes –
•all other chromosomes and the genes they
carry
 Sex-linked traits –
 traits that are
coded by an
allele on a sex
chromosome
 Why are there
more X sex
linked traits?
 X chromosome is
bigger than the y
chromosome
 Linked genes –
 genes that tend to be inherited together
 Usually means they are on the same
chromosome
Mutations
 Germ-cell mutation –
 mutations in organisms gametes
 Somatic cells –
 organisms body cells
 Somatic-cell mutation –
 mutations that occur in organisms body cells
 Lethal Mutations –
 mutations causing death (mostly before
birth)
 Some mutations beneficial – leads to natural
selection
Chromosome Mutations
 Deletion –
 loss of a piece of a chromosome (it breaks off)
 Inversion –
 chromosome part breaks off and reattaches
backwards
 Translocation –
 piece of chromosome breaks off and reattaches to a
non-homologous chromosome
 Nondisjunction –
 chromosome failing to separate during meiosis
 Get too many, or too few chromosomes (Trisomy 21)
 aneuploidy – having an abnormal number of chromsomes
Chromosome Mutations
Gene Mutations
 Point Mutation –
 substitution, addition or removal of a single
nucleotide in DNA
 Substitution –
 when one nucleotide replaces another
 Insertion Mutation –
 one or more nucleotide are added to a gene
(can lead to a frame-shift mutation)
 Frame-shift Mutation –
 deletion of a nucleotide, shifting all the codons,
changing all the amino acids
Gene Mutations
5-18 ATB
 What is a somatic cell mutation?
 Objectives:
 Practice pedigree problems
Human Genetics
•Pedigree –
•diagram that shows how a trait is inherited
over several generations
Hemophilia Pedigree from Queen Victoria
 Carriers –
 people who carry allele for a disorder, but do not
have the disorder
 (Heterozygous)
 Genetic disorders –
 any disease / disorder that have a genetic basis
 Polygenic –
 characteristics that are influenced by several
genes
 Examples:
 Skin color – six genes
 Other examples – eye color, height, hair color
 Complex characters –
 characteristics that are influenced strongly
by both environment and genes
 Sun = darker skin
 Height = several genes but also nutrition and
disease
 Multiple Alleles –
 genes that have three or more alleles
(usually 2)
 Example: Blood Type
 What are the blood types?
 ABO
 Three alleles –IA, IB, i
 Blood Types – A, B, AB, O
 Antigens – proteins, carbs etc on outside of RBC
 Antibodies – immuno proteins that destroy unrecognized
antigens
 http://nobelprize.org/educational_games/
medicine/landsteiner/
 “Blood typing activity” google – first link
 Codominance –
 when both alleles are expressed in the
phenotype (IA, IB – neither is dominant over
the other – both carbs are produced on cell
surface)
 In codominance, you see both traits
Red cow x white cow = roan cow
Codominance
 Incomplete dominance –
 mix between two parents
 Example:
 Straight hair mom x curly hair dad = wavy
haired child
 Red flower x white flower = pink flower
 In incomplete dominance, you see a mix
or blend of both traits
Incomplete Dominance
5-19 ATB
 What is the difference between
codominance and incomplete
dominance?
 Objectives:
 Discuss gene therapy
 Test Friday / or Monday
X-Linked Traits
 Traits carried on the X chromosome
 Who will show more X-linked disorders,
males or females? Why?
 Males – b/c they only have one X (Xy) (doesn’t
matter if trait is dominant or recessive)
 Example:
 Colorblindness – carried on X-chromosome
 Hemophilia – impaired blood clotting
Hemophilia
 X-linked
Hemophilia Pedigree from Queen Victoria
X-linked Dominant
 If mother affected 
equal chance of sons
/ daughters affected
 If father affected 
All daughters will
have, sons ok
 No carriers possible
X-Linked Recessive
 If mother carrier  50%
chance son will be
affected, no daughters
will have (thou they may
be a carrier)
 If father affected  Sons
will be ok, daughters
have 50% chance of
being a carrier)
Autosomal Dominant
 50 / 50 chance of
producing affected
children
 No carriers possible
Autosomal Recessive
 Occurs if both
parents are carriers
(only 25% of the
time)
 Carriers possible
5-21 ATB
 What is an X-linked trait?
 Objectives:
 Discuss gene therapy
 Review for test
 Test / Review sheet – Monday!
 Single-Allele Traits –
 traits caused by one dominant allele
 Huntington’s Disease –
 caused by one dominant allele. Onset is 3040 so parents have children before they
realize the have it
 Forgetfulness, irritability, muscle spasms
and mental illness, then death
 Genetic testing now beginning to be used to
determine if either parent has disease
Detecting Genetic Disease
 Amniocentesis –
 Dr. removes some amniotic fluid from the sac that
surrounds the fetus – can detect over 200 genetic
disorders
 Chorionic Villi Sampling –
 sample cells that grow between the uterus and
placenta
 Genetic Counseling –
 process of informing person about their genetic
make-up, and problems that may occur
 Predict likelihood of producing an affected child
Treating Genetic Diseases
 Sometimes treatment only relieves
symptoms
 Phenylketonuria (PKU) –
 body can’t break down the amino acid
phenylalanine into tyrosine – leads to mental
retardation
 Treatment – eliminate the specific amino acid
from the diet
 Cystic Fibrosis –
 mucus gets lodged in chest –
 Treatment – 45 minute sessions of pounding on
the back to break up mucus
Gene Therapy
 Gene Therapy –
 technique that places a healthy copy of a gene into the
cells of a person with the faulty gene
 Place the correct gene into the DNA of a virus –
introduce modified virus into lungs of person with
cystic fibrosis – infects cells, but also brings functional
gene – this improves condition, but only as long as
those cells survive (not permanent)
 Somatic Cell Gene Therapy –
 gene therapy in which body cells are altered
 Germ Cell Gene Therapy –
 attempt to alter sperm or eggs – ethical issues – what
if it effects the offspring in un-intended ways?
The End
5-24 ATB
 Test Today!
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Turn in your review sheet
Use a pencil
You MAY write on the test
#13 – “A” should read …(red x white = a
flower that is red and white)
NOT red and pink
 #20 --- D. Predict the possible
phenotypes of a child born to the F2
son if the son marries a female
carrier. It is an X-linked trait
 http://images.google.com/imgres?imgurl=
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