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Transcript of Final Genetics
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GENETICSis the science of heredity.
Heredity is the transmission of genetic orphysical traits from parent to offspring.
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CHARACTERISTICS
T hese are features youexhibit physically
( your looks)
Example: Eye color - green
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TRAITS
The different versions of a
characteristic
Example: blue, green, and
brown eyes
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INHERITANCE
´ Occurs when traits are
passed down from
parent to child.
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GREGOR MENDEL
* Austrian Monk* Considered the ´Father of Heredityµ* He conducted plant breeding
experiments in their monasterygarden.
* In 1865 he made his work public,units of inheritance.
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WHAT MAKES US UNIQUE ?
* Each of the 100 T rillion cells in our bodyexcept the red blood cells contains theentire human genome, in the nucleus ofevery cell is the genetic information
´blueprintµ to construct the individual.
* It is the Deoxyribonucleic acid (DNA)
Function of DNA* Genetic code for almost every organism.
* Provide template for protein synthesis.
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GENETIC INFORMATION
´ Gene ² basic unit of geneticinformation. Genes determine theinherited characters.
´
Genome ² the collection ofgenetic information.
´ Chromosomes ² storage units ofgenes.
´́ DNADNA - is a nucleic acid thatcontains the genetic instructionsspecifying the biologicaldevelopment of all cellular formsof life
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BASES OF DNAAdenine= A
Thymine= T
Guanine= GCytosine= C
A always pairs with T
C always pairs with G
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BASES OF RNAAdenine= A
Uracil= U
Guanine= GCytosine= C
G always pairs with C
T from the DNA = A in the RNAA from the DNA = U in the RNA
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DNA MODEL
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�DNA is information
�
DNA replicates in s-phase
� Daughter cells carry
�identical information
� Represented as astring
�over ={A,C,G,T}
� Main agent ofinformation
�transfer acrossgenerations
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�12
�DNA replication
�One ´parentalµ double
stranded DNA molecule totwo identical ´daughterµ
molecules (semiconservative)
� How?
�DNA unwinds and strandsare separated (replication
fork)
� Free nucleotides are
matched to exposed bases� DNA polymerase joins
nucleotides
�New and original strands
rewind
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�13
�Addition of nucleotides
� DNA polymerase
only adds nucleotides to
the 3· end ofDNA
� Synthesis
requires energy(gained from
hydrolysis of
phosphatebonds)
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�Central Dogma of Molecular Biology
DNA
í Double-stranded
í Long, immobileí Stable, inert
í Information across
generations
RNA:í Single-stranded
í Short, mobile
í Short-lived, reactive
í Information around
the cell Protein:
í Functional gene product
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�15
�Transcription
1-1 copying of the gene
sequence: ={A,C,G,U} Performed by enzymes
As needed, regulated by
nearby DNA sequences
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TRANSCRIPTION
DNA is copied into a complementarystrand of mRNA.
WHY?´ DNA cannot leave the nucleus. Proteins
are made in the cytoplasm. mRNA
serves as a ´messengerµ and carries theprotein building instructions to theribosomes in the cytoplasm.
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HOW TRANSCRIPTION OCCURS
1. RNA polymerase untwists and unzips asection of DNA (usually a single gene)from a chromosome.
2. RNA polymerase pairs free RNA nucleotidesto the exposed bases of one of the DNAstrands following base pair rules.
´ Uracil replaces thymine
´ Only 1 strand of DNA serves as a template,the other ´hangs outµ
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3. Newly synthesized mRNA separates fromtemplate DNA and DNA zips back up.
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TRANSCRIPTION EXAMPLE
´ T ranscribe the following DNA Sequence inmRNA
T AC CGG AT C CT A GGA T CA
AUG GCC UAG GAU CCU AGU
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PROTEINS
Structural and functional components of organisms.
´ Composed of amino acids
´ order of nucleotides in DNA determinesorder of amino acids in a protein
´ One gene codes for one protein
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DNA: TAC CTT GTG CAT GGG ATC
mRNA
AU
G GAA
CA
C GUA
CCCUA
GA.A MET G.A HIS VAL PRO STOP
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�22
Eukaryotic mRNA
exits the nucleus
Messenger RNA istranscribed inside
the nucleus but
translated outside Requires processing
into mature mRNA
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�23
mRNA Processing
Capping head,
Poly-A tail added
Most of the
pre-mRNA is
spliced out
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�24
Translation
Machinery:í Ribosome
í tRNA ´adaptorsµ
From mRNA
nucleotide triplets toamino acids
Uses the geneticcode: 4320+µstopµ
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25
A U G G G C U U A A A G C A G U G C A C G U U
T his is a molecule of messengerRNA.
It was made in the nucleus by
transcription from a DNA molecule.
mRNA
molecule
codon
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�26
A U G G G C U U A A A G C A G U G C A C G U U
A ribosome on the roughendoplasmic reticulum attaches
to the mRNA molecule.
ribosome
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�27
A U G G G C U U A A A G C A G U G C A C G U U
It brings an amino acid to the first
three bases (codon) on the mRNA.
Amino acid
tRNA molecule
anticodon
U A C
A transfer RNA molecule arrives.
T he three unpaired bases (anticodon)on the tRNA link up with the codon.
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�28
A U G G G C U U A A A G C A G U G C A C G U U
A peptide bond formsbetween the two aminoacids.
Peptidebond
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�29
A U G G G C U U A A A G C A G U G C A C G U U
T he first tRNA moleculereleases its amino acid and
moves off into the cytoplasm.
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�30
A U G G G C U U A A A G C A G U G C A C G U U
T he ribosome moves along themRNA to the next codon.
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�31
A U G G G C U U A A A G C A G U G C A C G U U
Another tRNA
molecule brings thenext amino acid intoplace.
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�32
A U G G G C U U A A A G C A G U G C A C G U U
A peptide bond joins thesecond and third amino
acids to form apolypeptide chain.
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�33
A U G G G C U U A A A G C A G U G C A C G U U
T he polypeptide chain gets longer.
T he process continues.
T his continues until a termination(stop) codon is reached.
T he polypeptide is thencomplete.
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�34
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�35
U C A G
U Phenylalanine Serine Tyrosine Cysteine U
U Phenylalanine Serine Tyrosine Cysteine C
U Leucine Serine Termination Termination A
U Leucine Serine Termination Tryptophan G
C Leucine Proline istidine Arginine U
C Leucine Proline Histidine Arginine C
C Leucine Proline Glutamine Arginine A
C Leucine Proline Glutamine Arginine G
A Isoleucine Threonine Asparagine Serine U
A Isoleucine Threonine Asparagine Serine C
A Isoleucine Threonine Lysine Arginine AA Methionine Threonine Lysine Arginine G
G Valine Alanine Aspartic acid Glycine U
G Valine Alanine Aspartic acid Glycine C
G Valine Alanine Glutamic acid Glycine A
G Valine Alanine Glutamic acid Glycine G
�1
st
b
a
s
e
3rd
b
a
s
e
THE GENETIC CODE
2n base
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´ DNA replication ² starts with the separation of DNAstrands. T hen enzymes use each strand as a template to
assemble new nucleotides into a complementary strand.Using the enzyme DNA polymerase, the cell synthesizesone daughter strand as a continuous piece, the other as aseries of shirt pieces which are then connected by theenzyme DNA ligase
´ Codons- triplets of bases
´ T ranscription ² in the nucleus, the DNA helix
unzips, and RNA nucleotides line up and hydrogen-bondalong one strand of the DNA, following the base-pairingrules.
�36
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´ As the single-stranded messenger RNA (mRNA)peels
away from the gene, the DNA strands rejoin. EukaryoticRNA is processed before leaving the nucleus as mRNA.Noncoding segments called introns are spliced out, and acap and tail are added to the ends.
´ Translation ²takes place in the cytoplasm. A ribosomeattaches to the mRNA and translates its message into a
specific polypeptide, aided by transfer RNAs (tRNAs)that act as interpreters. Each tRNAis a folded moleculebearing a base triplet called as anticodon on one end; a
specific amino acid is added to the other end.
�37
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CHROMOSOMES
The DNA in every cell is located in rod like
segments called chromosomes
Chromosomes occurs in pairs in every cell of our
body except in the sperm and ovum.
Chromosomes numbers are the same for each
specie.
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CHROMOSOME NUMBERS
Species Diploid # Haploid #
Cattle 60 30
Swine 38 19Sheep 54 27
Horse 64 32
Human 46 23
Chicken 78 39
Goat 60 30
Donkey 62 31
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CHROMOSOMES
´ There are 2 sex chromosomes included inthe diploid number of the chromosomes.
´ All of the other chromosomes are referredto as autosomes.
´ In mammals if the sex chromosomes arealike, XX it results in a female.
´ If the sex chromosomes are different, XY it results in a male.
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CHROMOSOME LOGICALSTRUCTURE
´ Locus ² location of a gene/markeron the chromosome.
´
Allele ² one variant form of agene/marker at a particular locus .
�41
Locus1
Possible Alleles: A1,A2
Locus2Possible Alleles: B1,B2,B3
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SEX DETERMINATION´ Females contribute an X chromosome towards the sex
of their offspring.
´ Males can contribute an X or a Y chromosome toward
the sex of their offspring.´ Absence of an Y chromosome results in a the embryo
developing into a female.
´ Presence of an Y chromosome results in the embryo
developing into a male.
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SEX DETERMINATION
´ Gametogenesis =
Formation of gametes
through meiosis.´ Male = 4 viable
spermatids
´ Female = 1 viable
ovum, 3 polar bodies.
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HUMAN GENOME
Most human cellscontain 46 chromosomes:
´ 2 sex chromosomes (X,Y):XY ² in males.XX ² in females.
´ 22 pairs of chromosomesnamed autosomes.
�44
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GENOTYPES PHENOTYPES
´At each locus (except for sex chromosomes)there are 2 genes. T hese constitute theindividual·s geno type at the locus.
´T he expression of a genotype is termed a
p heno typ e . For example, hair color, weight,or the presence or absence of a disease.
�45
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GENOTYPES PHENOTYPES (EXAMPLE)
´ Eb- d om inan t allele.
´ Ew- r ecess iv e allele.
�46
genotypes
phenotypes
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DOMINANT VS. RECESSIVE
�47
� A d om inan t allele isexpressed even if it is
paired with a recessiveallele.
�A r ecess iv e allele is
only visible when pairedwith another recessiveallele.
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ONE LOCUS INHERITANCE
�48
heterozygote homozygote
21A | A a | a
A | a 3 4 a | a
A | a 5 6 a | a
Male
Female
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MENDEL·S 1ST LAW
�49
T wo members of a gene pair segregate from each other into
the gametes, so half the gametes carry one member of the
pair and the other half carry the other member of the pair.
Y / y y / y
½ y/y
½ Y/y
½ y
½ Y
all yGamete
production
Gamete
production
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CALCULATING PROBABILITIES
´ We want to predictpatterns of inheritanceof traits and diseases in
pedigrees.
´ E.g., we want to knowthe likelihood that a
dog chosen at randomfrom the studypopulation will have blueeyes.
�50
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PUNNET SQUARE
´ Angus- Black coat color is dominant.
´ BB = Homozygous Dominant and Black
´ Bb = Heterozygous and is black
´ bb = Homozygous recessive and red
´ A heterozygous bull is mated to 50 homozygous
recessive cows.
´ How many calves are black?
´ How many calves are red?
´ What is the genotypic and phenotypic ratios?
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PUNNET SQUARE
B b
b
b
Bb bb
Bb bb
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RESULTS
´ 2 heterozygous = Bb
´ 2 HomozygousRecessive bb
´ 25 Black, 25 Red
´ Genotypic ratio = 0:2:2
´ Phenotypic ratio =
2 Black: 2 Red
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WHAT ARE SEX LINKED GENES?
´ Some recessive genes are attached to the X
and Y chromosomes
´ Humans: Colorblindness and Baldness are onthe X chromosomes
´ In Men, traits expressed anytime present
´ In Women, must have two recessives to show
trait
´ Children get baldness from mothers
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IF DAD IS BALD,WILL YOU BE
BALD?
X Y
X XX X Y
XX XYX
B
B
B
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BALDNESS IS CARRIED BY THE
MOTHER
X Y
X XX X Y
XX XYX
BB B
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WHAT IF MOM IS BALD?
X Y
X XX X Y
XX XYX
BB B
B B B
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WHAT IS INCOMPLETE
DOMINANCE
?´ If both genes express themselves
´ Shorthorn Cattle: Red male mated to a White
female = Roan calf
´ RR crossed rr = Rr
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PUNNET SQUARE
´ Shorthorn Cattle
´ RR = Red
´
rr = white´ Rr = roan
´ If a red bull (RR) is mated to a white cow (rr),
what color will the calves be?
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SHORTHORN: RED XWHITE
R R
r
r
Rr Rr
Rr Rr
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PUNNET SQUARE
´ If a red bull (RR) is mated to a roan (Rr) cow,
what color will the calves be?
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SHORTHORN: RED X ROAN
R R
R
r
RR RR
Rr Rr
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WHAT IF BOTH PARENTS ARE ROAN?
R r
R
r
RR Rr
Rr rr
X li k d I h i
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�64
X-linked Inheritance
Different results obtainedfrom reciprocal crossesbetween red-eyed andwhite-eyed Drosophila.
: T he geneExplanationresponsible for eye-coloris X-linked. Females have
2 X-chromosomes, whilemales have 1 X-chromosomeand 1 Y-chromosome.
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MENDEL·S 2ND LAW
´ Different gene pairs assort independentlyin gamete formation.
�65
Gene pairs on SEPARATE CHROMOSOMESassort independently at meiosis.
T is ´la µ is tr e only in some ases.
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MEDICAL GENETICS
When studying rare disorders, 6 general patternsof inheritance are observed:
´ Autosomal recessive´
Autosomal dominant´ X-linked recessive´ X-linked dominant´ Codominant
´
Mitochondrial
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MEDICAL GENETICS (CONT.)
Autosomal recessive
´ T he disease appears
in male and femalechildren ofunaffected parents.
´ e.g., cystic fibrosis
�67
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MEDICAL GENETICS (CONT.)
Autosomal dominant
´ Affected males andfemales appear in eachgeneration of thepedigree.
´ Affected mothers andfathers transmit the
phenotype to both sonsand daughters.
´ e.g., Huntington disease.
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MEDICAL GENETICS (CONT.)
X-linked recessive
´ Many more males thanfemales show the disorder.
´ All the daughters of anaffected male are´carriersµ.
´ None of the sons of anaffected male show the
disorder or are carriers.´ e.g., hemophilia
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MEDICAL GENETICS (CONT.)
X-linked dominant
´ Affected males pass thedisorder to all daughters
but to none of their sons.´ Affected heterozygous
females married tounaffected males pass thecondition to half their sons
and daughters´ e.g. fragile X syndrome
�70
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MEDICAL GENETICS (CONT.)
Codominant inheritance
´ T wo different versions(alleles) of a gene can beexpressed, and eachversion makes a slightlydifferent protein
´ Both alleles influence thegenetic trait or determinethe characteristics of the
genetic condition.´ E.g. ABO locus
�71
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MEDICAL GENETICS (CONT.)
Mitochondrial inheritance´ T his type of inheritance
applies to genes inmitochondrial DNA
´ Mitochondrial disorderscan appear in everygeneration of a family andcan affect both males andfemales, but fathers do notpass mitochondrial traitsto their children.
´ E.g. Leber's hereditaryoptic neuropathy (LHON)
�72
QUESTION #1
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QUESTION #1
�73
1 2
� Write the genotypes in every possible place.� If individuals 1 and 2 marry, what is the probability thattheir first child will be sick?
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QUESTION #2
´
PKU is a human hereditary disease resulting frominability of the body to process the chemicalphenylalanine (contained in protein that we eat).
´ It is caused by a recessive allele with simple Mendelian
inheritance.
´ Some couple wants to have children. T he man has asister with PKU and the woman has a brother with PKU.T here are no other known cases in their families.
´ What is the probability that their first child willhave PKU ?
�74
QUESTION #2 SOLUTION
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QUESTION #2-SOLUTIONHIGHLIGHTS
�75
P/p P/p P/p P/p
p/p p/pP/- P/-
P ² the normal allelep ² the mutant allele
QUESTION #3
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QUESTION #3
�76
1 2 3 4 5 6 7 8 9 10
a. What is the most likely mode of inheritance ?
b. What would be the outcomes of the cousin marriages1 x 9, 1 x 4, 2 x 3, and 2 x 8 ?
� T
he disease israre
.
QUESTION #3 SOLUTION
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QUESTION #3-SOLUTIONHIGHLIGHTS
a. Observations:« After the disease is introduced into the family in generation
#2, it appears in every generation dominant!« Fathers do not transmit the phenotype to their sons
X-linked!
b. T he outcomes:« 1 x 9: 1 must be A/a
9 must be A/Y« 1 x 4: 1 must be A/a
4 must be a/Y« 2 x 3: 2 must be a/Y
3 must be A/a« 2 x 8: 2 must be a/Y
8 must be a/a
�77
Same
All normal
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NOTES
´ Cystic fibrosis ² disease affecting the mucus lining of the
lungs, leading to breathing problems and other difficulties
´ Huntington disease - or Huntington's chorea is an inherited
disorder characterized by abnormal body movements called
chorea, and loss of memory. There also is evidence thatdoctors as far back as the Middle Ages knew of this devastating disease. The incidence is 5 to 8 per 100,000. It takes its namefrom the New York physician George Huntington who firstdescribed it precisely in 1872.
�78
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NOTES
´ Hemophilia-illness that impair the body's ability tocontrol bleeding.
´ Fragile X syndrome - is a genetic condition thatcauses a range of developmental problems including
learning disabilities and mental retardation. Usuallymales are more severely affected by this disorder thanfemales. In addition to learning difficulties, affectedmales tend to be restless, fidgety, and inattentive.Affected males also have characteristic physical
features that become more apparent with age.
�79
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NOTES -CONT
´ DNA - a pair of molecules joined by hydrogen bonds: it is organizedas two complementary strands, head-to-toe, with the hydrogenbonds between them. Each strand of DNA is a chain of chemical"building blocks", called nucleotides, of which there are fourtypes:adenide (abbreviated A), cytozyne (C), guanine (G) andthymine (T ).
´ Mitochondria, which are structures in each cell that convertmolecules into energy, each contain a small amount of DNA.
´ A chromatid forms one part of a chromosome after it has coalescedfor the process of mitosis or meiosis. During either process, the
word "chromosome" indicates a pair of two exactly identical("sister") chromatids joined at the central point of each chromatid,called the centromere.
�80
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NOTES -CONT
´ Mitosis is the process by which a cell separates itsduplicated genome into two identical halves
´ Meiosis is the process that transforms one diploidinto four haploid cells.
´ Reciprocal cross a cross, with the phenotype of each sex reversed as compared with the originalcross, to test the role of parental sex on inheritancepattern. A pair of crosses of the type genotypeA(female) X genotype B(male) and genotype B(female)
X genotype A(male).