Non-Mendelian Genetics

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Non-Mendelian Genetics
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What color offspring would you get when you cross
a pure (homozygous) red snapdragon with a pure
white snapdragon?
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Oddly Enough, Neither Red Nor White

• Snapdragon Flower Color is controlled by
  Incomplete Dominance and a new 3rd phenotype is
  seen.

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How does Incomplete Dominance work?
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Incomplete Dominance is a Blending

• Like Paint, the RED Pigment MIXES with the
  WHITE to create PINK-FLOWERED offspring

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Incomplete Dominance can be seen in

• Horses
• ( Chestnut x Cremello ? Palomino)
• Snapdragons
• Japanese Four O Clocks
• Many flowers exhibit incomplete dominance.

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Allele Notation

• HOW DO YOU WRITE OUT THE GENOTYPE WHEN BOTH
  ALLELES ARE DOMINANT?

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You Must Use Different Letters

1. Choose different letters to represent each form
   (In this case well use W for the white allele
   and R for the Red allele).
2. Remember to always use CAPITAL letters. This is
   incomplete DOMINANCE.

RR
WW
RW
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SoThe Cross Between Pure Snapdragons Looks Like
This
R
R
RW
RW
W
RW
RW
W
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Youve Seen A Cross between Pure Snapdragons, now
do the Punnet Square for a cross between two
hybrids (heterozygotes).

• What are the alleles of a heterozygous
  snapdragon?
• RW
• What is the genotypic ratio?
• 1 RR 2 RW 1 WW
• What is the phenotypic ratio?
• 1 Red 2 Pink 1 White

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What kind of genetics do these organisms exhibit?
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Codominance
A cross between 2 tabbies (the heterozygotes)
results in 1 black 2
tabbies 1 tan cat

• The same ratios as Incomplete Dominance occur
• A ratio of 121 for both genotype and phenotypes
  of a monohybrid cross
• ?
• Different Phenotype
• The two original phenotypes are combined to give
  a SPOTTED or MULTICOLORED phenotype.

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Notation for Codominance

1. Choose a letter to represent the gene.
2. Choose different letters to represent each of the
   alleles.
3. Take the letters representing the alleles and
   turn them into superscripts.
4. Combine the two. Remember to use capital
   letters.

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Writing out the Genotype

1. Were going to use C to represent Coat Color of a
   shorthorn cow.
2. Roan coat color is a combination of Red and White
   hair so well use R to represent Red and W to
   represent white.
3. R ? R and W ? W
4. C R ? CR and C W ? CW
5. So a Red Cow would be CRCR , a white cow would be
   CWCW, and a roan cow would be CRCW

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Codominance occurs in

• Shorthorn Cow (White Red)
• Blue Roosters (White Black)
• Human Blood Typing (AB)
• Tabby Cats (Black and Tan Fur)

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Lets Practice

• Tabby cats exhibit codominance between tan and
  black fur.
• Can Tan Cat be heterozygous? Why or Why not?
• If you mate a tabby with a black cat, what is the
  phenotypic ratio of their offspring?
• If the offspring of two cats are composed of 36
  tabbies and 40 black cats, what are the parental
  phenotypes and genotypes?

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Blood Typing

• Human blood typing is an example of both
  Codominance and Multiple Alleles
• What does Multiple Alleles Mean?

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The Alleles

• A and B blood types are coded for by the
  allelesIA and IB respectively. These two
  alleles are CODOMINANT.
• Blood type O is coded for by the allele i and is
  recessive to both IA and IB (notice the lower
  case letter).

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Alleles and Their Blood Types
i i O
IA IA IA i A
IB IB IB i B
IA IB AB
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Lets Practice

• Could a man with AB blood have an AB child with a
  woman with type O blood?
• If a child has type B blood, what are all the
  possible blood types for his/her parents?
• A paternity test is being performed. The child
  has type A blood. The mother is type A.
  Potential Dad 1 has type B blood. Potential Dad
  2 has type O blood. Who is the father?
• Challenge What two parents could produce the
  most diverse children as far as blood type is
  concerned?

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Codominance

• Sickle-cell Disease
• -common in people of African descent
• -sickled allele causes hemoglobin to change and
  red blood cell forms a crescent shape cant
  carry oxygen well

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Codominance

• Genotypes
• BN BN normal blood cells
• BNBS normal blood cells and sickled cells
• BSBS sickled blood cells

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HOMEWORK

• Finish Bikini Bottom Genetics Packet

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Sex-linked Traits

• Traits (genes) located on the sex chromosomes
• Sex chromosomes are X and Y
• XX genotype for females
• XY genotype for males
• Many sex-linked traits carried on X chromosome

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Sex-linked Traits
Example Eye color in fruit flies
Sex Chromosomes
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Sex-linked Trait Problem

• Example Eye color in fruit flies
• (red-eyed male) x (white-eyed female) XRY
  x XrXr
• Remember the Y chromosome in males does not
  carry traits.
• RR red eyed
• Rr red eyed
• rr white eyed
• XY male
• XX female

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Sex-linked Trait Problem

• Example Eye color in fruit flies
• (red-eyed male) x (white-eyed female) XRY
  x XrXr
• Remember the Y chromosome in males does not
  carry traits.
• RR red eyed
• Rr red eyed
• rr white eyed
• XY male
• XX female

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Sex-linked Trait Solution
50 red eyed female 50 white eyed male
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Female Carriers
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Question Is it possible for a female carrier of
hemophilia to have a daughter with hemophilia?
XH Xh
Xh
XH Xh
XhXh
Y
XH Y
Xh Y
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Epistasis
When one gene hides the effects of another
gene 2 genes determine coat color E gene
can mask B gene
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Epistasis
Ee or EE Can have dark pigment ee cant have
dark pigment B darker Dark pigment b
lighter Dark pigment
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Dosage Compensation
Females have 2 doses of X Males only have 1
dose of X To balance this difference one of
the X chromosomes is inactivated or turned off
X chromosome Genes necessary For male/female Y
chromosome Genes necessary For male only
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Dosage Compensation

• Chromosome inactivation One X in each cell is
  randomly inactivated.
• Orange cells where X chrom. with black allele
  is inactivated
• Black cells where X chrom. With orange allele
  is inactivated

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• Barr bodies
• Inactivated X
• chromosome forms
• a condensed dark spot
• in nucleus

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Polygenic TraitsA trait that is controlled by
more than one gene.
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Polygenic Traits

• So, instead of only 2 alleles contributing to a
  trait, there can be 4 or 6 or 8, etc. alleles
  contributing to a trait.
• Skin color the more dominant alleles for each
  gene, the darker the skin

AABbCc darker skin aaBbCc lighter skin
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Gene Linkage

• Mendel studied genes on different chromosomes, so
  they assorted independently many combinations
• Genes located close together on the same
  chromosome are said to be linked they get
  passed down to gametes together dont assort
  independently

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