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LAELEL
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OIATDMNN
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EEOYOSHTRZGU
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HNTPPEOYE
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1. Designate letters which will represent thegenes/traits
2. Write down the genotypes (genes) of each
parent3. List the genes that each parent can
contribute.
4. Draw a Punnett square - 4 small squares inthe shape of a window.
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5. Fill in each box of the Punnett square bytransferring the letter above and in front of
each box into each appropriate box. As a
general rule, the capital letter goes first and alowercase letter follows.
6. List the possible genotypes and phenotypes of
the offspring for this cross.
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Capital letters represent dominant
traits, and lowercase letters
represent recessive traits.
T= tall t = short
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Father - TT
Mother - tt
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Genetic Information
Gene basic unit of geneticinformation. Genes determine theinherited characters.
Genome the collection ofgenetic information.
Chromosomes storage units ofgenes.
DNADNA - is a nucleic acid thatcontains the genetic instructionsspecifying the biologicaldevelopment of all cellular formsof life
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Chromosome Logical Structure
Locus location of a gene/markeron the chromosome.
Allele one variant form of agene/marker at a particular locus.
Locus1
Possible Alleles: A1,A2
Locus2
Possible Alleles: B1,B2,B3
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Human Genome
Most human cellscontain 46 chromosomes:
2 sex chromosomes (X,Y):XYin males.XXin females.
22 pairs of chromosomesnamed autosomes.
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Genotypes Phenotypes
At each locus (except for sex chromosomes)
there are 2 genes. These constitute the
individuals genotype at the locus.
The expression of a genotype is termed a
phenotype. For example, hair color, weight,or the presence or absence of a disease.
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Genotypes Phenotypes (example)
Eb- dominant allele.
Ew- recessive allele.
genotypes
phenotypes
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Dominant vs. Recessive
A dominantallele is expressed even if it is
paired with a recessive allele.
A recessive allele is only visible whenpaired with another recessive allele.
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One Locus Inheritance
heterozygote homozygote
21A | A a | a
A | a 3 4 a | a
A | a5 6 a | a
Male
Female
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Two 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.
Mendels 2nd Law
Y / y y / y
y/y
Y/y
y
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.
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X-linked Inheritance
Different results obtained from
reciprocal crosses between red-
eyed and white-eyed
Drosophila.
: The geneExplanation
responsible for eye-color
is X-linked. Females have
2 X-chromosomes, whilemales have 1 X-chromosome
and 1 Y-chromosome.
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Mendels 3rd LawIndependent Assortment
Different gene pairs assort independentlyin gamete formation.
Gene pairs on SEPARATE CHROMOSOMESassort independently at meiosis.
This law is true only in some cases.
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Medical Genetics
When studying rare disorders, 6 generalpatterns of inheritance are observed:
Autosomal recessive
Autosomal dominant X-linked recessive X-linked dominant Codominant
Mitochondrial
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Medical Genetics (cont.)
Autosomal recessive
The disease appears
in male and femalechildren ofunaffected parents.
e.g., cystic fibrosis
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Medical Genetics (cont.)
Autosomal dominant
Affected males and
females 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 arecarriers.
None of the sons of anaffected male show the
disorder or are carriers. e.g., hemophilia
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Medical Genetics (cont.)
X-linkeddominant
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
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Medical Genetics (cont.)
Codominant inheritance
Two 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
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Medical Genetics (cont.)
Mitochondrial inheritance This type of inheritance
applies to genes in
mitochondrialD
NA
Mitochondrial disorderscan appear in everygeneration of a family andcan affect both males andfemales, but fathers do not
pass mitochondrial traitsto their children. E.g. Leber's hereditary
optic neuropathy (LHON)
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Example:
Four oclock plant
White , Red and Pink
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SpongeBob SquarePants recentlymet SpongeSusie Roundpants at adance. SpongeBob is heterozygousfor his square shape, butSpongeSusie is round. Square shape
is dominant to round. Create aPunnett square to show thepossibilities that would result if SpongeBob and SpongeSusie had
children. List the possible genotypesand phenotypes for their children.
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TT - square shape
Tt - square shape,
and tt - round
shape
Phenotypic Ratio:
Square shape-2Round shape -2 or
2:2
Genotypic Ratio:
Tt 2 and tt 2 or
2:2
T t
t Tt ttt Tt tt
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A horizontal line between two symbolsrepresents a mating .
The offspring are connected to each other bya horizontal line above the symbols and to theparents by vertical lines.
Roman numerals (I, II, III, etc.) symbolizegenerations. Arabic numerals (1,2,3, etc.)symbolize birth order within each generation.
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