Genetics

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Genetics

• What DNA is telling us!

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Learning Goals

• The student will investigate and understand
  common mechanisms of inheritance and protein
  synthesis. Key concepts include
• prediction of inheritance of traits based on the
  Mendelian laws of heredity
• genetic variation (mutation, recombination,
  deletions, additions to DNA)
• use of genetic information and
• exploration of the impact of DNA technologies.

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vocabulary terms

• INHERITANCE or HEREDITY-
• The genetic transmission of characteristics
  from parent to offspring

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vocabulary terms
GENETICS The study of the transmission of
heredity
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vocabulary terms

• HOMOLOGOUS CHROMOSOMESA pair of matching
  chromosomes in an organism- with one inherited
  from Mom one from Dad.

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vocabulary terms

• AUTOSOME-
• Any chromosome that is NOT a sex chromosome.
• In humans there are 22 pairs

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vocabulary terms

• GENOTYPE- the genes present in the DNA of an
  organism. 
• Genotypes are represented by
• 2 letters -because (as a result of sexual
  reproduction)
• 1 gene from MOM 1 gene from DAD 2 genes (2
  letters) for offspring

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vocabulary terms

• Now, it turns out there are usually 3 possible
  GENOTYPES
• 1. 2 capital letters (like "TT")
• 2. 1 of each ("Tt")
• 3. 2 lowercase letters ("tt").
• Since WE LOVE VOCABULARY, each possible combo
  has a term for it.

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vocabulary terms

• HOMOZYGOUS GENOTYPE has 2 capital or 2 lowercase
  letters (ex TT or tt)
• ("homo" means "the same")
• -A zygote is a fertilized egg-
• Sometimes the term "PUREBRED" is used instead of
  homozygous.

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vocabulary terms

• HETEROZYGOUS GENOTYPE has 1 capital letter 1
  lowercase letter (ex Tt)
• ("hetero" means "other")
•  
• A heterozygous genotype can also be referred to
  as HYBRID and sometimes the organism is called a
  CARRIER

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vocabulary terms

• Let's Summarize
• Genotype- genes present in an organism
• (usually abbreviated as 2 letters)
• TT homozygous purebred
• Tt heterozygous hybrid
• tt homozygous purebred

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vocabulary terms

• PHENOTYPE- how the trait physically shows-up in
  the organism it is the observable traits present
  in an organism
• What the organism LOOKS like
• Examples of phenotypes blue eyes, brown fur,
  striped fruit, yellow flowers

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vocabulary terms

• POLYGENIC INHERITANCE- a trait controlled by two
  or more genes that may be on the same or on
  different chromosomes
• Examples of polygenic inheritance eye color,
  skin color, and height

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vocabulary terms

• ALLELES- alternative forms of the same gene. 
  Alleles for a trait are located at corresponding
  positions on homologous chromosomes called loci.

ALLELES
Chromosome from MOM
A b C d e
Chromosome from DAD
A B c d E
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(P)
Chromosome from DAD P
Chromosome from MOM p
(p)
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vocabulary terms

• When 1 allele masks (hides) the effect of
  another, that allele is called DOMINANT
• and the hidden allele is called RECESSIVE.

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vocabulary terms

• Dominant alleles are represented by a CAPITAL
  letter
• Recessive alleles are represented by a LOWERCASE
  letter

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What are Dominant Genes?

• Dominant Genes gene overshadows the other
• Angus Cattle black is dominant, red is not

Dominant BB - homozygous dominant or Bb -
heterozygous
Recessive bb ONLY- Homozygous recessive
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What are Dominant Genes?

• Hereford white face is dominant

Dominant WW or Ww
Recessive ww ONLY
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What are Recessive Genes?

• The gene that is overshadowed by a dominant gene
• Recessive genes can only express themselves if
  BOTH genes are recessive
• So the genotype MUST be homozygous recessive

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What are Recessive Genes?

• Black wool is recessive to white wool.

Dominant WW or Ww
Recessive ww ONLY
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What are Recessive Genes?

• Some types of dwarfism are recessive to average
  size.

Dominant DD or Dd
Recessive dd ONLY
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What are Recessive Genes?

• Albinism (Albino) is recessive to pigmented.

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What makes an organism the way that it is?

• NATURE vs. NURTURE
• Traits that are expressed through genes can be
  inherited. Characteristics that are acquired
  through environmental influences, such as
  injuries or practiced skills, cannot be inherited.

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Gregor Mendel (1822-1884)

• Austrian monk
• Called the Father of Genetics" for his study of
  the inheritance of 7 traits in pea plants.

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Gregor Mendel (1822-1884)

• The traits that Mendel chose to study were easily
  observable in 2 distinct forms.

EX. Stem Height - tall vs. short Pod Shape -
round vs. wrinkled Flower Color white vs.
purple Seed Color green vs. yellow
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Gregor Mendel (1822-1884)

• The significance of Mendel's work was not
  recognized until the turn of the 20th century
• Its rediscovery prompted the foundation of
  genetics.

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Genotype Symbol Genotype Vocabulary Phenotype
TT homozygous DOMINANT or purebred tall tall
Tt heterozygous or hybrid tall
tt homozygous RECESSIVE  or purebred short short
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• Geneticists apply mathematical principles of
  probability to Mendels laws of heredity in order
  to predict the results of simple genetic crosses

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• Mendels laws of heredity are based on his
  mathematical analysis of observations of patterns
  of the inheritance of traits.
• The laws of probability govern simple genetic
  recombinations.
• To see this we use a Punnett Square

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Punnett Squares

• To complete a Punnett square, we use a letter to
  represent each allele.
• We represent the dominant allele with a capital
  letter, and the recessive allele is given the
  same letter but in lowercase.
• If there is only ONE TRAIT to look at the
  probability of occuring this is a MONOHYBRID
  CROSS

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Punnett Squares

• For the pea plant flowers
• dominant purple color P
• recessive white color p.
• If both parents( P generation) are purebred,
  then the purple colored parent must be PP and the
  white colored parent must be pp.

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How can we predict these results?
Homozygous-dominant
We complete the possible combinations.



P
P
P
P
p
p
p
p
P
P
p
p
Homozygous-recessive
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These results show that all the F1 (1st filial
generation) offspring are all purple colored
hybrids.
P P
p Pp Pp
p Pp Pp
100 purple offspring
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Heterozygous - hybrid
We can use another Punnett square to predict the
F2 (2nd filial generation) offspring.



P
p
Heterozygous - hybrid
P
P
P
P
p
p
P
p
p
p
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Heterozygous - hybrid
The results are always mathematically the same,
a 31 ratio with 75 purple 25 white offspring



P
p
Heterozygous - hybrid
P
P
P
P
p
p
P
p
p
p
Phenotypic ratio 31 Genotypic ratio 121
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Heterozygous - hybrid
A genotype ratio is possible gene combination
results you expect from a cross
Phenotypic ratio 31 Genotypic ratio 121



P
p
Heterozygous - hybrid
P
P
P
P
p
A phenotype ratio is possible appearance results
you expect from a cross.
p
P
p
p
p
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Dihybrid cross

• You now are determining the probability for TWO
  TRAITS.
• The Punnnett square NOW has 16 possible
  combinations so all the ratios are out of 16.
• To determine the possible gamete combinations you
  have to FOIL, but I have a short cut, too.

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Dihybrid cross
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Dihybrid cross
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Dihybrid cross
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Dihybrid cross
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Dihybrid cross
dihybrid cross practice
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Dihybrid cross
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Incomplete dominance

• When both alleles are present, they are both
  expressed in the phenotype.
• The hybrid is a blend of both alleles.
• When expressing incomplete dominant alleles, both
  alleles are may represented by different
  capitalized letters. YOU NOW HAVE 3 possible
  phenotypes!!!!

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Incomplete dominance F1 generation
Homozygous



R
R
R
W
R
W
W
W
R
R
W
W
Homozygous
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Incomplete dominance F1 generation
100 pink offspring



R
R
R
W
R
W
W
W
R
R
W
W
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Incomplete dominance F2 generation
Heterozygous



R
W
R
R
R
W
R
W
R
W
W
W
Heterozygous
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Incomplete dominance F2 generation
Heterozygous
A 121 ratio with 25 red, 50 pink 25
white offspring



R
W
R
R
R
W
R
W
R
W
W
W
Heterozygous
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codominance

• When both different alleles are present, they are
  both expressed in the phenotype.
• The hybrid EXPRESSES both alleles so both are
  clearly seen.
• When expressing codominant alleles, alleles are
  may represented by different capitalized letters.

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Codominance in humans
Blood Type phenotypic ratio 1111 1 type
A 1 type B 1 type AB 1 type O



IA
IO
IA
IB
IB
IO
IB
IO
IA
IO
IO
IO
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Codominance in humans
Blood Type A B are equally strong. O is
recessive IAIO or IAIA is Type A IBIO or IBIB
is Type B IAIB is Type AB IOIO is type O
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Codominance in humans
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Codominance in humans
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codominance

• EX.

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codominance

• EX.

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Sex-Linked Traits
Boy or Girl? The Y Chromosome Decides
Y chromosome
X chromosome
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What are Sex Linked Traits?

• In 1910, Thomas Morgan discovered traits linked
  to sex chromosomes in fruit flies.
• Some genes are attached to the X and Y
  chromosomes
• EXAMPLE In humans, colorblindness and hemophilia
  are found on the X chromosomes

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What are Sex Linked Traits?

• Since it is usually on the X chromosomes, in Men,
  traits expressed anytime present
• In Women, must have two genes to show trait
• Sons can ONLY inherit sex-linked traits from
  their mothers since dads can only give the Y
  chromosome to their sons

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Punnett Square What sex will the offspring be?
50 chance of a male or a female child.
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Colorblindness
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Colorblindness can be carried by the mother so
both parents can have normal color vision
butthey can still have a colorblind child
Phenotype 25 colorblind males 25 carrier
females 25 normal males 25 non-carrier females
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If Dad is colorblind, will you be colorblind?
Phenotype 0 colorblind males 100 carrier
females
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What if Mom is colorblind and dad has normal
vision?
Phenotype 100 carrier females 100 colorblind
males
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Genetic Diversity

• The sorting and recombination of genes in sexual
  reproduction results in a great variety of gene
  combinations in the offspring of any 2 parents.
• Do you look EXACTLY like your brothers sisters?

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Genetic Diversity

• Genetically diverse populations are more likely
  to survive changing environments.
• Greater variation within the species makes a
  population better suited to adaptation to changes
  in the environment.

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Genetic Diversity

• Leopard populations around the world are in
  danger because of inbreeding.

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Genetic Diversity

• There is very little genetic variation between
  any 2 individuals.

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Genetic Diversity

• This makes them VERY susceptible to disease
  will likely lead to their extinction.

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Genetic Diversity

• Recombination and mutation provide for genetic
  diversity.
• Inserting, deleting, or substituting DNA bases
  can alter genes.
• An altered gene in a sex cell may be passed on to
  every cell that develops from it, and MAY cause
  an altered phenotype.

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recombination

• Crossing-over
• the physical exchange of chromosomal material
  between chromatids of homologous chromosomes
  during MEIOSIS.
• Result Generation of new combinations of genes
  (alleles).

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recombination

• Occurs in prophase I of meiosis I
• Generates diversity

Creates chromosomes with new combinations of
alleles for genes A to F.
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recombination
A
a
a
A
Letters denote genes Case denotes alleles
B
b
b
B
c
C
C
c
D
D
d
d
E
E
e
e
F
F
f
f
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recombination
a
A
a
A
Alleles have crossed over to produce new gene
combinations
B
b
B
b
c
c
C
C
D
D
d
d
E
E
e
e
F
F
f
f
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Chromosomal Errors

• Sometimes entire chromosomes can be added or
  deleted by mistakes during anaphase, resulting in
  a genetic disorder such as Trisomy 21 (Down
  syndrome) or Monosomy X (Turners syndrome).

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Chromosomal Errors

• NONDISJUNCTION the failure of chromosomes to
  separate properly in meiosis. Gametes with extra
  or too few chromosomes result.
• Can cause diseases such as Downs Syndrome,
  Turners and Klinfelters.

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Chromosomal Errors

• POLYPLOIDY organisms with entire extra sets of
  chromosomes
• Results in the death of the fetus in animals
• Often occurs in plants and causes the fruits and
  flowers to be larger. EX. bananas, lilies

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A Karyotype is an Arranged Picture of Chromosomes
At Their Most Condensed State
Note that almost all chromosomes come in
homologous pairs.
Boy or girl?
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Karyotype
Boy or Girl?
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Normal or abnormal Karyotype?male or female?
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Pedigrees

• Pedigree charts show a record of the family of an
  individual.
• It can be used to study the transmission of a
  hereditary condition.
• It is particularly useful when there are large
  families and a good family record over several
  generations.

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Autosomal Dominant
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• Genetics Quiz 5 all responses in complete
  sentences
• Using the proper vocabulary, describe a single
  gene cross between a homozygous dominant and a
  homozygous recessive organism for one trait.
• Describe the survival benefits of an organism
  doing meiosis.
• What are the reasons to study genetics?
• What is a karyotype and what does it show?
• What exactly is a Punnett square used for?

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Ethical Moral Concerns

• The potential for identifying and altering
  genomes raises practical and ethical questions.

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Ethical Moral Concerns

• Cloning is another morally charged issue facing
  us today.
• Cloning is the production of genetically
  identical cells and/or organisms.

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Ethical Moral Concerns

• Dolly was famous all over the world because of
  the way she was born, in 1996. She was the
  world's first cloned mammal.

Dolly the sheep 1996 - 2003
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Ethical Moral Concerns

• Other cloned animals

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Ethical Moral Concerns

• Transgenic organisms also known as Genetically
  modified organisms
• These are organisms that have DNA from a
  different source or RECOMBINANT DNA
• Much of our food is transgenic or GMOs
  genetically modified organisms, like corn,
  soybeans, mangos and strawberries

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Ethical Moral Concerns
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Genetics in the News

• Human Genome Project a 1986 DOE and NIH project
  to identify and map the approximately
  20,00025,000 genes of the human genome completed
  in 2003

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Genetics in the News

• Medical or Criminal Forensics- because every
  organism has its own unique DNA
• DNA fingerprinting or profiling is done where the
  test sample is matched with actual DNA of humans
  and other organisms
• This has been used as evidence in criminal cases
  and to determine relatedness between individuals

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DNA Fingerprinting

• Restriction enzymes cut unknown DNA into small
  pieces at certain points
• The pieces are placed in wells at the top of a
  gel and electricity is run through it
• A standard with known DNA sizes is placed in at
  least one well to compare
• The different sized fragments (measured in number
  of base pairs) stop at certain points and the
  unknown is compared with the known samples

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Genetics in the News

• PCR- polymerase chain reaction
• A process that allows biotechnologists to make
  many copies of a small sample DNA in research or
  for identification in criminal cases when they
  use DNA fingerprinting.
• http//bldg6.arsusda.gov/pooley/soy/cregan/pcr_an
  ime.html

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