Mendelian Genetics1

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Mendelian Genetics

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• Cells come from pre-existing cells

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Cell Division
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Cell Differentiation

• Why is it then your cells have the same DNA, but
  they all have different structure and function?

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• Levels of organization
• Specialized cells perform specific functions.

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Notes

• Although almost every cell in your body has the
  same DNA, they all look and function differently.
  They are all specialized cells.
• Cells develop into their mature forms through the
  process of cell differentiation.
• Cells differ because different combinations of
  genes turn on or off (gene expression).

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• Red gene turned on
• Black gene turned off
• UGACGGGUAGGACUGAGGAUUUAAAGGCC

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• Red gene turned on
• Black gene turned off
• UGACGGGUAGGACUGAGGAUUUAAAGGCC

Outer skin cells
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• Red gene turned on
• Black gene turned off
• UGACGGGUAGGACUGAGGAUUUAAAGGCC

Middle bone cells
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• Red gene turned on
• Black gene turned off
• UGACGGGUAGGACUGAGGAUUUAAAGGCC

Inner intestines
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Stem Cells

• Stem cells have the ability to
• divide and renew themselves
• remain undifferentiated in form
• develop into a variety of specialized cell types

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Kinds of Stem Cells
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• A cells location in an embryo helps determine
  how it will differentiate.

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Chromosomes

• DNA is coiled into structures called chromosomes
• Almost all the cells in your body have the same
  number of chromosomes

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Gene Map
Exact location on chromosomes
Chromosome 2
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• DNA plus proteins is called chromatin.

• One half of a duplicated chromosome is a
  chromatid.
• Sister chromatids are held together at the
  centromere.

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Notes

• Karyotype display of all chromosomes of an
  individual
• A human has 23 pairs of chromosomes, for a total
  of 46
• One pair are sex chromosomes
• The other 22 pairs are autosomes

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Notes

• Homologous chromosomes are sisters in that they
  contain the genes for a particular trait
• One comes from the mother
• One comes from the father

homologous chromosomes
sister chromatids
sister chromatids
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How Many Chromosomes?

• A human cell originally has 46 chromosomes.
• How can this human cell divide into two cells
  with the same kinds and number of chromosomes as
  the parent (original) cell?

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Notes

• Mitosis - process where body makes more cells
  used in growth and repair
• Produces genetically identical cells (same number
  and kinds of chromosomes)
• Results in two diploid (2n) daughter cells
• Diploid means pairs of homologous chromosomes
• Occurs in somatic (body) cells
• Involved in asexual reproduction

46 x 2 92
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46
Somatic (body) cells
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Notes

• Asexual Reproduction reproduction where the
  offspring has only one parent.
• Offspring is genetically identical to parent

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How Many Chromosomes?

• A human cell originally has 46 chromosomes.
• How can a cell have 46 chromosomes if it has to
  have chromosomes from both a male and a female,
  whose original cells contain 46 chromosomes?

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Notes

• Meiosis process where body makes cells involved
  in sexual reproduction
• Produces genetically unique cells
• Results in four haploid (n) cells (one half of
  the homologous pairs of chromosomes)
• Occurs in the gametes (sperm and egg)

46 x 2 92
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46
23
23
23
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Notes

• Sexual reproduction process where gametes unite
  to produce a new organism

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Notes
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Diploid vs. Haploid

• Are the following cells diploid or haploid?
• In humans . . .
• Parent cell 46 chromosomes
• Daughter cell 46 chromosomes
• Daughter cell 23 chromosomes
• In dogs . . .
• Daughter cell 78 chromosomes
• Daughter cell 39 chromosomes
• Parent cell 78 chromosomes
• The cell is a result of fertilization
• The cells are gametes

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Notes

• Gametes develop from germ cells
• located in the ovaries and testes.
• are sex cells egg and sperm.
• have DNA that can be passed to offspring.

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Notes

• Fertilization results when egg and sperm unite

Fetus
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Notes

• Zygote fertilized egg cell
• Embryo called an embryo from implantation up
  until week 8
• Fetus called a fetus after week 8 until birth

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Heredity
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In Vitro Fertilization
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Fraternal Twins
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Identical Twins
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How Twins are Formed
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Why are humans such unique individuals?
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Notes

• Genetic variation genetic differences between
  organisms within the same population
• Sources of genetic variation
• Mutations
• Sexual Reproduction
• Segregation Independent assortment
• Crossing over

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Notes

• Segregation when homologous chromosomes
  separate during meiosis
• Independent assortment process by which genes
  segregate into different combinations

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Notes

• Crossing over when non-sister chromatids
  exchange genetic segments during meiosis

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During meiosis in humans

• chromosomes can line up 223 or 10 million (107)
  different ways in meiosis
• so each person can produce 10 million (or 107)
  different types of gametes

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• What happens when chromosomes fail to separate
  correctly?

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Notes

• Nondisjuction when chromosomes fail to separate
  correctly during meiosis

Homologous chromosomes fail to separate
Meiosis I Nondisjunction
Meiosis II
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Downs Syndrome
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Characteristics of a child with Down
Syndrome -wide, rounded face -equal length
fingers -mentally challenged -webbed
neck -enlarged tongue
Normal female karyotype with 46 chromosomes
Down syndrome karyotype with an extra chromosome
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Meiosis vs. Mitosis

• Did the following cell undergo mitosis or
  meiosis?
• The daughter cells are genetically identical to
  the parent cell
• The daughter cells are haploid
• The daughter cells are not genetically identical
  to the parent cell
• The result is 4 daughter cells
• The result is 2 daughter cells
• The daughter cells are involved in asexual
  reproduction
• The cells form gametes
• The daughter cells are diploid
• The cells form somatic cells
• The daughter cells are involved in sexual
  reproduction
• Crossing over occurs here
• Law of segregation occurs here
• Law of independent assortment occurs here

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Notes

• Genes come in pairs that code for a trait.
• Eye color, Hair color, Height, etc.
• Alleles different forms of the same gene for a
  particular trait
• Alleles for eye color would be green, brown,
  blue, etc.
• Genes and alleles are represented as letters
• A pair of genes have alleles H and h. These may
  represent a trait like hair color. For example,
  H black hair, h brown hair

H allele for black hair
Pair of genes
Homologous chromosomes
h allele for brown hair
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Practice

• Are the following gene pairs or an allele?
• J
• PP
• Ll
• g
• Bb

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Notes

• Genotype genetic make up of an organism
• Hh
• Phenotype physical characteristics of an
  organism
• black hair

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Practice

• Are the following genotypes or phenotypes?
• Yy
• SS
• Round eyes
• Rr
• Webbed fingers

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Notes

• Dominant a type of allele that covers or
  dominates over the effects of another
  represented by a capital letter

• Recessive a type of allele that is covered by
  the effects of the dominant allele represented
  by a lower case letter

H
h
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Practice

• Are the following alleles dominant or recessive?
• H
• R
• i
• g
• M
• a

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Practice

• H is the dominant allele for blonde hair. h
  is the recessive allele for black hair. What are
  the phenotypes for the following individuals?
• HH blonde hair
• hh black hair
• Hh blonde hair

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Notes

• Homozygous 2 identical alleles
• Also known as Purebred
• BB or bb
• Heterozygous 2 different alleles
• Also known as hybrid
• Bb

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Notes

• Homozygous dominant 2 dominant identical alleles
• AA or BB
• Homozygous recessive 2 recessive identical
  alleles
• aa or bb

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Practice

• Are the following genotypes homozygous dominant,
  homozygous recessive, or heterozygous?
• Hh
• RR
• Ii
• gg
• Mm
• aa

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Notes

• P Parent generation
• F1 offspring of parent generation
• F2 offspring of F1 generation

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Notes

• Punnett Square tool to predict genotypes
  (genes) and phenotypes (physical traits) of
  offspring

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Probability
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Notes

• Monohybrid cross involves one trait
• For example, eye color
• A Brown eyes
• a blue eyes

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How to do a Cross using Punnett Squares

1. Determine the traits and alleles
2. Determine the parents genotype
3. Set-up the Punnett Square
4. Fill-in Punnett Square
5. Determine probabilities of possible types of
   offspring (genotypes and phenotypes)

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Practice

• Dimples is dominant over no dimples. A woman who
  is homozygous for dimples has children with a man
  who has no dimples.
• What is the probability of having a child with no
  dimples?

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Alleles D Dimples d no dimples
Genotypes-Phenotypes DD - Dimples Dd - Dimples dd
no dimples
Female DD
eggs
D
D
Offspring
sperm
d
Dd
Dd
100 Dd dimples 0 dd no dimples
Male dd
Dd
Dd
d
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Notes

• Carrier an organism who carries the allele for a
  specific trait, but the allele is not expressed
  in the organisms phenotype
• Usually are heterozygous (Aa or Gg)

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Practice

• Cystic Fibrosis is caused by a recessive allele.
• A woman (Nn) and a man (Nn) are normal but they
  are also carriers for Cystic Fibrosis.
• What is the chance that their child will have
  Cystic Fibrosis?
• What are the chances of having a child that is a
  carrier for the disease?

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Alleles N Normal n Cystic Fibrosis
Genotypes-Phenotypes NN - Normal Nn - Normal nn -
Cystic Fibrosis
Female Nn
n
N
Offspring
N
Nn
NN
Each child would have a 25 chance of having
Cystic Fibrosis
Male Nn
Nn
nn
n
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Notes

• Dihybrid cross involves 2 traits
• For example, seed color and seed shape
• Seed color
• Y yellow
• y green
• Seed shape
• R round
• r wrinkled

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Practice

• In pea plants, green seeds are dominant over
  yellow seeds, and smooth seeds are dominant over
  wrinkled seeds. One parent is heterozygous for
  seed color and homozygous dominant for seed
  shape. The other parent is homozygous recessive
  for seed color and heterozygous for seed shape.
  Predict the genotypes and phenotypes of the
  offspring using proportions (fractions).

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Genotypes/Phenotypes AA green BB smooth Aa
green Bb smooth Aa yellow bb wrinkled
Alleles A green a yellow B smooth b
wrinkled
Genotypes of Parents AaBB x aaBb
Offspring 4/16 AaBB, green smooth 4/16 aaBB,
yellow smooth 4/16 aaBb, yellow smooth 4/16 AaBb,
green smooth
AB
aB
aB
AB




aB
AaBB
AaBB
aaBB
aaBB
AaBb
AaBb
aaBb
aaBb
ab
aB
AaBB
AaBB
aaBB
aaBB
AaBb
aaBb
aaBb
ab
AaBb
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Notes

• Sex chromosomes are X and Y
• In humans
• XX is female
• XY is male

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Sex Determination

• Are there more males than females in the world?

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Calico Cats

• Codominant and X-linked trait

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Sex-linkage

• Sex-linked traits are carried on the sex
  chromosomes (X or Y). Women have two X
  chromosomes, while men have an X and a Y.
• Most sex-linked traits that have been studied
  well are X-linked. Women need two copies of a
  recessive X-linked trait to show the trait. Men
  only need one.

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Notes

• X-linked inheritance when genes are expressed on
  the X chromosome.
• For example, colorblindness, hemophilia, muscular
  dystrophy

Father (normal vision)
Normal vision
Colorblind
Male Female
Daughter (normal vision)
Son (normal vision)
Mother (carrier)
Daughter (carrier)
Son (colorblind)
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How X-linkage works

• Only women can be carriers of X-linked traits,
  since they have two X chromosomes.
• Men can pass an X or a Y to their children. Women
  only have an X.

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Romanovs and Revolution

• A Genetic History Mystery

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The Romanovs
Tsar Nicholas II
Alexandra
Olga
Tatiana
Alexei
Marie
Anastasia
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Grigory Rasputin
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Hemophilia

• Caused by a single, recessive allele.
• This allele codes for a blood-clotting protein.
  If the protein is defective, then the blood does
  not clot properly.
• Untreated, victims often die in childhood or teen
  years, rarely live to adulthood.

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The Windsor Pedigree
This pedigree shows who had hemophilia in the
Windsor family line. Why only males? And who are
the carriers?
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The Completed Pedigree
Notice only women can be carriers. Why? And
heres the real mystery Why are there no
carriers before Victoria?
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Color Blindness (X-linked)
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Things to Remember

• When doing Punnett squares for X-linked traits,
  we track not just the alleles, but the
  chromosomes they are carried on.
• This is only for traits on the sex chromosomes,
  not for traits on the other(somatic) chromosomes.

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Practice

• Are there more colorblind males than females?
• Predict the genotypes and the phenotypes of the
  offspring if the female is normal but a carrier
  for colorblindness, and the male is normal.
  Colorblindness is an X-linked and recessive.

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Alleles B Normal b Colorblind
Genotypes-Phenotypes XBXB Normal female XBXb
Normal carrier female XbXb colorblind
female XBY normal male XbY colorblind male
Female XBXb
Xb
XB
Offspring
25 XBXB normal female 25 XBXb carrier
female 25 XBY normal male 25 XbY colorblind
male
XB
XBXb
XBXB
Male XBY
XBY
XbY
Y
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Notes

• Multiple alleles 3 or more alleles that code
  for a single trait.
• For example, blood type, sickle cell anemia, and
  Huntingtons Disease

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Blood Type
Safe Transfusions
Antigen on Red Blood Cell
Phenotype (Blood Type
Genotype
From
To
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Whos the Daddy?

• If the child is blood type A (IAi) and the mother
  has AB blood (IAIB), who could potentially be the
  father? The man with type B blood (IBi) or the
  man with type O blood (ii)?

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Alleles IA A antigen IB B antigen i no
antigen
Genotypes-Phenotypes IAIA or IAi blood type
A IBIB or IBi blood type B IAIB blood type
AB ii blood type O
Female IAi
i
IA
Offspring
25 IAIB type AB 25 IBi type B 25 IAi type
A 25 ii type O
IB
IBi
IAIB
Male IBi
IAi
ii
i
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Alleles IA A antigen IB B antigen i no
antigen
Genotypes-Phenotypes IAIA or IAi blood type
A IBIB or IBi blood type B IAIB blood type
AB ii blood type O
Female IAi
i
IA
Offspring
50 IAi type A 50 ii type O
i
ii
IAi
Male ii
IAi
ii
i
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Notes

• Polygenic traits are produced by two or more
  genes.

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Notes

• Phenotype is a combination of genotype and
  environment.
• sex of sea turtles
• height

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Albino Porcupine

• An epistatic gene can interfere with other genes.

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Notes

• Codominance both alleles expressed.
• For example, in chickens, red feathers are
  codominant with white feathers.
• B red
• Y white
• BB
• YY
• BY

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Notes

• Codominance both alleles expressed.
• For example, in chickens, red feathers are
  codominant with white feathers.
• B red
• Y white
• BB red
• YY white
• BY red and white

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Codominance
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Practice

• In carnations, if red flowers are codominant with
  white flowers, what is the phenotype of a
  heterozygous individual?
• RR
• WW
• RW

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Practice

• In carnations, red flowers are codominant with
  white flowers. Predict the proportion of
  genotypes and the phenotypes of the offspring if
  one plant has red flowers and the other has white
  flowers?

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Alleles R red W white
Genotypes-Phenotypes RR - red WW - white RW red
and white
RR x WW
R
R
Offspring
100 RW red and white flowers
W
RW
RW
RW
RW
W
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Notes

• Incomplete dominance allele that does not
  completely dominate or cover the effects of
  another.
• For example, in beta fish, blue scales are
  incompletely dominant over green scales.
• B blue
• b green
• BB blue
• bb green
• Bb turquoise

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Incomplete Dominance
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Incomplete Dominance
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Practice

• In mice, if black fur is incompletely dominant
  over white fur, what are the possible different
  phenotypes?
• BB
• bb
• Bb

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Practice

1. In mice, black fur is incompletely dominant over
   white fur. Predict the proportion of genotypes
   and the phenotypes of the offspring if one mouse
   has black fur and the other has gray fur.

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Alleles B black b white
Genotypes-Phenotypes BB - black bb - white Bb
gray
BB x Bb
B
B
Offspring
50 BB black fur 50 Bb gray fur
B
BB
BB
Bb
Bb
b
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Pedigree
A circle represents a female.
A square represents a male.
A horizontal line connecting a male and female
represents a marriage.
A vertical line and a bracket connect the parents
to their children.
A half-shaded circle or square indicates that a
person is a carrier of the trait.
A circle or square that is not shaded indicates
that a person neither expresses the trait nor is
a carrier of the trait.
A completely shaded circle or square indicates
that a person expresses the trait.