Genetics of Heredity

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Genetics of Heredity

• Biology 12

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The Dawn of Genetics

• Genetics the study of heredity
• which is the transmission of characteristics from
  parents to offspring

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Gregor Johann Mendel

• born on July 22, 1822
• to peasant parents in a small agrarian town in
  Czechoslovakia
• In 1843 he entered an Augustinian monastery in
  Czechoslovakia
• He was later sent to the University of Vienna to
  study

The above photo is from http//www.open.cz/project
/tourist/person/photo.htm.
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The garden of the Augustinian Convent in Brno.
part of the foundations of the greenhouse that
Mendel used
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Mendel studied Pea Plants - Why?

• The male part of the flower (stamen) was easily
  removed to prevent self-pollination.
• Pea flowers are easy to cross-pollinate
• They were easy to grow.

• The pea flower

Pistil
Stamen
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Mendel Isolated 7 pairs of contrasting traits.

• Dominant Recessive

Round wrinkled
Yellow seed Green seed
Purple flower White flower
Images from Purves et al., Life The Science of
Biology, 4th Edition, by Sinauer Associates
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In each case, one characteristic was dominant and
one was recessive
Inflated pod Constricted pod
Green pod Yellow pod
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And the last 2 traits he selected
Flower postion Axial is dominant over terminal
Tall is dominant over short.
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• Mendel tested all 34 varieties of peas available
  to him through seed dealers. The garden peas were
  planted and studied for eight years.
• Mendel's experiments used some 28,000 pea plants.
  
• So just imagine what life would have been like
  living in the same monastery as Brother Gregor??

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Mendel formulated 2 basic laws that are still
used today

• Law of Segregation - during gamete formation the
  pair of genes responsible for each trait
  separates so that each gamete receives only one
  gene for each trait
• Law of Independent Assortment - genes for
  different traits segregate independently during
  gamete formation.

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Genetic Terminology you will need to know

• A gene is a heritable factor that controls a
  specific characteristic a region of DNA that
  controls a hereditary characteristic.
• An allele is one specific form of a gene,
  differing from other alleles by one or a few
  bases only and occupying the same gene locus
  (location) as other alleles of the gene an
  alternate form of a gene.
• For example, some people have genes that give
  them brown eyes while others have genes which
  result in green or blue eyes.

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More Terminology

• Genotype  the alleles of an organism, typically
  represented by two letters.  (Bb, TT, Gg)
• Phenotype  the characteristics of an organism
  (ie what they look like)

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And More Terminology

• Dominant allele  an allele that has the same
  effect on the phenotype whether it is present in
  the homozygous or heterozygous condition. (the
  dominant allele will always be displayed in the
  phenotype)
• Recessive allele  an allele that only has an
  effect on the phenotype when present in the
  homozygous state.

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Yet More Terminology

• Homozygous having two identical alleles of a
  gene. (pure)
• Heterozygous  having two different alleles of a
  gene.  (hybrid)

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What are dominant genes?

• The gene that express itself, the powerful and
  dominant gene.
• It has the power to overshadow the recessive gene
  when there is complete dominance.
• You will always be given a clue about the
  dominant gene you dont need to memorize all of
  them!
• Some examples are
• White faced in cattle
• Droopy ears in swine
• Polled in cattle
• Black coat color in Angus cattle

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What are Recessive Genes?

• The gene that is overshadowed by a dominant gene
• Recessive genes can only express themselves in
  the absence of the dominant gene
• Black wool vs white (Ww) (ww)
• Green peas vs. yellow peas (Cc) (cc)

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What would these plants look like?

• Wrinkled or smooth?
• (remember S smooth, s wrinkled)
• SS ?????
• ss ?????
• Ss ?????
• NOTE a plant with different GENOTYPE (SS and
  Ss) will have the SAME PHENOTYPE (they will both
  appear wrinkled because the smooth allele is
  dominant over the wrinkled)

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Punnett Grid
Egg
Offspring Genotypes 50 XX 50 XY Offspring
Phenotypes 50 female 50 male
Female
Female
Sperm
Male
Male
Label the grid with Parental genotypes, gametes,
offspring genotype and phenotype
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Punnett Square example

• In Angus cows, 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 a homozygous
  recessive cow.
• How many calves are black?
• How many calves are red?
• What is the genotypic and phenotypic ratios?

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Punnett Square
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Results

• 2 heterozygous Bb
• 2 Homozygous Recessive bb
• Genotypic ratio 022 (BBBbbb)
• Phenotypic ratio
• 2 Black 2 Red

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F1 Generation

• Genetic Cross
• Mating
• F1
• Children
• 1st generation

Parents B b
B BB Bb
B BB Bb
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2nd Filial Generation- F2

• F1
• F2

B B
b Bb Bb
b Bb Bb

• Children of the cross between the children of an
  F1
• mating among F1
• Only after pure x pure

B b
B BB Bb
b Bb bb
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Monohybrid Crosses

• 1.In peas, green color is dominant to yellow.
  What will be the genotype and phenotypes of
  crossing a hybrid green plant with a pure yellow?
• 2.In cats, long tails are dominant to short
  tails.
• a) show the results of the F1 generation if a
  homozygous long tailed cat is mated with a short
  tailed cat.
• b) If two of the F1 cats are mated, give the
  results of the F2 generation that is produced.

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More Monohybrid Practice

• 3.If a heterozygous black guinea pig is mated
  with a homozygous recessive white guinea pig,
  what will be the genotypic and phenotypic results
  of the F1 generation?
• 4. In humans, the gene that causes freckles is
  dominant to the gene for no freckles. If a
  freckled man whose father had no freckles mates
  with a freckled woman whose mother had no
  freckles, then answer the following
• a) What genotypes and phenotypes are expected in
  their children?
• b) If this couple had 8 children, how many would
  you expect to have no freckles? Be pure for the
  freckles allele? To have freckles? To be hybrid
  for the freckles allele?

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Genes with Multiple Alleles

• Some genes have more than two alleles that
  control a certain trait and this is known as
  multiple alleles. 
•  In humans for example, the gene that controls
  the ABO
• blood types has
• three alleles.  The
• gene has an A
• allele, B allele,
• and an O allele.

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Blood types contd

• The A allele is dominant to the O allele
• The B allele is dominant to the O allele
• The A and B alleles are co-dominant to each other
  which means that they will both be expressed in
  the phenotype and people with AB blood will have
  both the A protein and the B proteins on the
  outside of their red blood cells.

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Blood Types contd

• The O allele is recessive to both the A and B
  allele so a person must be homozygous O
• in order for that allele to show in the
  phenotype. 

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• In terms of genotype and phenotype, human blood
  groups are expressed as follows

Phenotype Genotype
O ii
A IAIA  or   IAi
B IBIB  or   IBi
AB IAIB 
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Blood Type Practice

• What are the possible blood types to result from
  crossing
• A type O mother with a type AB father
• A pure type A mother with a pure type B father
• A hybrid type A mother with a hybrid B father
• If a child with blood type O has a mother with
  blood type A and a father with blood type B, what
  are the parents genotypes for blood type?

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More Blood Type Practice

• 3. Lord Hooke has type AB blood and his wife,
  Lady Hooke has type A blood. They have four
  children Ida who is type A, Ann who is type B,
  Tom who is type O and Helen who is type A. Lady
  Hooke has been unfaithful to her husband and one
  of the children is not really Lord Hookes child.
  Which child is it? Show a cross to prove your
  answer.
• 4. Reyhan has type A blood. Reyhans father has
  type O blood and her mother has type A blood.
  What is Reyhans genotype?

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Codominance

• There are other examples of codominance most
  commonly flowers

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Codominance Practice

• The alleles for red flower color CR and for white
  flower color CW are codominant. And a plant with
  the genotype CRCW will have pink flowers. Show a
  punnett square, genotypic and phenotypic ratios
  for a cross between a plant with red flowers and
  one with pink flowers.

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Sex Chromosomes

• The sex chromosomes determine the gender of the
  offspring.  Humans have two sex chromosomes, an X
  and a Y chromosome. 
• The X chromosome
• is much larger and
• carries many genes
• as compared to the
• smaller Y chromosome.

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Sex Chromosomes Contd

• If a human embryo contains two X chromosomes it
  will develop into a female, and if it contains
  one X and one Y chromosome it will develop into a
  male.
• Eggs produced by females contain only an X
  chromosomes while males produce both X and Y
  sperm so the gender of the offspring is always
  determined by the father.

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Genes on the X and Y

• Due to the fact that the Y chromosome is smaller
  than the X chromosome, some genes are absent from
  the Y chromosome that can be found on the X
  chromosome.

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Sex linkage

• A gene that is located on either the X or Y
  chromosome is known as a sex-linked gene. 
• Therefore, sex-linkage is the association of a
  particular characteristic with sex due to the
  fact that the gene controlling that
  characteristic is located on one of the sex
  chromosomes.

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Colour Blindness and Hemophilia

• Color blindness (red-green) and hemophilia are
  two examples of sex-linkages in humans.  Both are
  sex-linked recessive disorders that are produced
  by a recessive sex-linked allele on the X
  chromosome.
• Because the traits are sex-linked recessive, the
  recessive allele (lower case letter) is the one
  carrying the disorder.

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Notation

• According to conventional notation
• The color blindness allele is Xb
• The normal color vision allele is XB
• The hemophilia allele is Xh
• The non-hemophilia (normal) allele is XH

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So this should really be Xb and XB, right!
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So this should also be Xb and XB, right!
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Sex linked Genes

• Due to the fact that most sex-linked traits are
  located on the X chromosome, females can be
  either
• homozygous or
• heterozygous for
• the genes because
• they have two X
• chromosomes. 

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Recessive Disorders

• Recessive disorders can only be expressed in
  females if they carry the allele on both of the X
  chromosomes. 
• Due to this fact many females are carriers they
  have one dominant allele and one recessive allele
  and can pass either allele on to their
  offspring. 
• However in males,  if the recessive gene is
  present it will always be expressed.

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Sex-Linked Practice

• Predict the genotypes and phenotypes of the
  following crosses
• A man with hemophilia mates with a homozygous
  normal woman.
• A woman who is a carrier and a normal man.
• A woman who is a carrier and a hemophiliac man.
• A phenotypically normal man, who has a
  hemophiliac brother, and a homozygous normal
  woman.
• A normal sighted woman, whose father was
  color-blind, and a color-blind man
• A color-blind woman and a normal vision man.

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Two mice were mated. One had long ears and the
other had short ears. The cross produced F1
offspring in the following proportions 12
long-eared Bunnies, 10 short-eared bunnies. When
two of the long-eared F1 offspring were crossed,
F2 offspring were produced in the following
combinations 36 long-eared, 13 short-eared. a.
Explain which allele is dominant for ear
length b. Give the phenotypes of the parents c.
Give the genotypes of the F1 generation Explain
your answers and show your work.
Yay for more practice!!
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If Dad is bald, will you be bald?
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What if Baldness is carried by the mother?
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What if Mom is bald?
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Genotype or Gamete

• Genotype contains two copies of the gene.
• AaBB
• Gamete (sex cells) contains only one copy of the
  gene.
• AB
• Determine the possible gametes of AaBB
• AB aB

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Gamete or Genotype

• State if its a gamete or genotype.
• Aa
• D
• DdEeFFgg
• sRtxyq
• AaBBeeFF
• adgEFT

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List all the possible gametes.

• From the genotype AaBb
• AB
• Ab
• aB
• ab

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Two-Trait Crosses Dihybrid Crosses

• Mendel also studied the inheritance of two traits
  at once
• (ie round yellow plants (RRYY) X wrinkled green
  (wwyy)

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Two-trait continued

• Remember, the law of segregation stated that each
  gamete must contain ONE allele from each trait
• therefore, the gametes of a round, yellow parent
  are R, Y and the gametes of a wrinkled, green
  parent are r, y.

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Dihybrid crosses

• Dihybrid crosses are made when phenotypes and
  genotypes composed of 2 independent alleles are
  analyzed.
• Process is very similar to monohybrid crosses.
• Example
• 2 traits are being analyzed
• Plant height (Tt) with tall being dominant to
  short,
• Flower color (Ww) with Purple flowers being
  dominant to white.

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Dihybrid cross example continued

• Take the offspring and cross them since they are
  donating alleles for 2 traits, each parent in the
  f1 generation can give 4 possible combination of
  alleles. TW, Tw, tW, or tw. The cross should
  look like this. (The mathematical foil method
  can often be used here)

F2 Generation
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Dihybrid cross example continued

• Note that there is a 9331 phenotypic ratio.
  9/16 showing both dominant traits, 3/16 3/16
  showing one of the recessive traits, and 1/16
  showing both recessive traits.
• Also note that this also indicates that these
  alleles are separating independently of each
  other. This is evidence of Mendel's Law of
  independent assortment

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Two-trait Cross example
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Dihybrid Cross Practice

• In guinea pigs, black coat colour is dominant
  over white, and short hair length is domninant
  over long. Indicate the genotypes and phenotypes
  of the following crosses
• A. A guinea pig that is homozygous for black and
  heterozygous for short hair is crossed with a
  white, long-haired guinea pig
• B. A guinea pig that is homozygous for black and
  for long hair is crossed with a guinea pig that
  is heterozygous for black and for short hair.

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One more Dihybrid Cross Practice

• Black coat colour in cocker spaniels is dominant
  over white coat colour. Solid coat pattern is
  dominant over spotted pattern. A male that is
  black with a solid pattern mates with three
  females
• The mating with female A, which is white and
  solid, produces four pups two black, solid and
  two white, solid.
• The mating with female B, which is black and
  solid produces a single pup which is white,
  spotted.
• The mating with female C, which is white and
  spotted, produces four pups one white solid, one
  white spotted, one black solid, one black
  spotted.
• Indicate the genotypes of the parents.

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Pedigree Charts
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Practice Draw your own

• Please complete the worksheet called Pedigree
  Analysis.
• Youll draw a pedigree of your family and analyse
  new pedigrees!

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Pedigree Analysis

• Indicate the affected individuals
• Indicate the carriers
• Indicate the method of inheritance

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Mystery at the Termond Estate!!!

• Super-fun!
• Who was the thief???
• Who is not truly a blood relative???

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Case Study Marfan Syndrome

• Marfan Syndrome is inherited as an autosomal
  dominant trait. It is a defect of connective
  tissue formation.
• Some of its common features include Tall, long,
  thin limbs (relative to height), prominent
  shoulder blades, spinal curvature, protruding or
  caved-in breastbone, flat feet, dislocated eye
  lens and/or detached retina, long fingers and
  thumbs, heart valve abnormalities and weakening
  of the aortal wall.

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Marfan Syndrome

• Use the patient histories to create a pedigree
  for Annes family and answer the analysis
  questions that follow the histories.