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What is the genotype?. Hairless. Lecture 4. Continued. Example of Probabilities Using Sex Linkage:. X H Y × X H X h. X H X H X H X h X H Y1/4 normal male X h Y1/4 male with hemophilia. 1/2 normal females. Sex malefemale normal hemophilia. Sex malefemale

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What is the genotype?

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What is the genotype?

Hairless


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Lecture 4

Continued


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Example of Probabilities Using Sex Linkage:

XHY× XHXh

XHXH

XHXh

XHY1/4 normal male

XhY1/4 male with hemophilia

1/2 normal females


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Sex

malefemale

normal

hemophilia


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Sex

malefemale

normal 1/41/23/4

hemophilia 1/401/4

1/21/2


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Conditional Probabilities

  • P(affected child) = 1/4


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Conditional Probabilities

  • P(affected child) = 1/4

  • P(hemophilia / male)?


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Sex

malefemale

normal 1/41/23/4

hemophilia 1/401/4

1/21/2


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Conditional Probabilities

  • P(affected child) = 1/4

  • P(hemophilia / male) = 1/4 = 1/21/2


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Conditional Probabilities

  • P(affected child) = 1/4

  • P(hemophilia / male) = 1/4 = 1/21/2

  • P(hemophilia / female) = 0 = 0 1/2


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Lecture 5

Exceptions to Mendel’s Ratios


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Sex Influenced


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Sex Influenced

  • Traits for which the expression of the phenotype depends on the sex of the individuals. Can occur with both autosomal or sex-linked loci.


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Example of Sex Influence:

Presence of horns in sheep:

Polled -- without horns

Horned -- with horns


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Sheep Example:

P = polled

p = horned


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Horned malePolled female

pp × PP


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Horned male Polled female

pp × PP

All progeny Pp


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Horned male Polled female

pp × PP

  • All progeny Pp but,

  • female -- polled P > p

  • male -- horned p > P


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malefemale


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malefemale

PPPolledPolled


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malefemale

PPPolledPolled

ppHornedHorned


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malefemale

PPPolledPolled

PpHorned

ppHornedHorned


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malefemale

PPPolledPolled

PpHornedPolled

ppHornedHorned


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malefemale

PPPolledPolled

PpHornedPolled

ppHornedHorned

p > P


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Sex Limited


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Sex Limited

  • A phenotype that is expressed in only one sex.


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Sex Limited

  • A phenotype that is expressed in only one sex.

  • Examples:

  • Antlers -- deer

  • Color -- pheasants and cardinals

  • Milk production -- dairy


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X Inactivation

In a sex-linked locus:


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X Inactivation

In a sex-linked locus:

T = black hairT = t

t = orange hair


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Cat Fanciers’ Association


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Cat Fanciers’ Association


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PhenotypeGenotype

malefemale

blackXTYXTXT

orange XtYXtXt


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PhenotypeGenotype

malefemale

blackXTYXTXT

orange XtYXtXt

tortoiseshellXTXt (unique)

-- calico = tortoiseshell with S_ --


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ss XTXt

Cat Fanciers’ Association


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S_ XTXt

Cat Fanciers’ Association


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  • Occasionally a tortoiseshell male happens:


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  • Occasionally a tortoiseshell male happens:

  • Nondisjuncture -- failure of chromosomes to separate properly during meiosis


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ParentsXTXt × XTY


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ParentsXTXt × XTY

GametesXTXt×XT Y


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ParentsXTXt × XTY

GametesXTXt×XT Y

Zygotes

  • XTXtXTtortoiseshell female

  • XTblack female

  • Ydies

  • XTXtYtortoiseshell male


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Non-disjuncture can occur in any chromosome.


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Non-disjuncture can occur in any chromosome.

  • trisomic 21 -- Down’s Syndrome -- incidence by age

Maternal ageIncidence/1000

 250.5

301.0

356.0

40 12.0

45 21.0

Not near as dramatic in males!

(?)


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Non-disjuncture can occur in any chromosome.

  • trisomic 21 -- Down’s Syndrome

  • trisomic 13 -- Patau -- 1/5000

  • trisomic 18 -- Edwards -- 1/14000


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Lethal Conditions


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Lethal Conditions

  • Gene or genotype that leads to the death of the individual.


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Postnatal Lethal Condition (Abnormalities)


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Postnatal Lethal Condition (Abnormalities)

Parrot jaw in cattle:

P = normalP > p

p = parrot jaw


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Pp × Pp


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Pp × Pp

3 P_ + 1 pp

normal parrot jaw (dies at young age)


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Embryonic Lethal

L = normalL > l

l = lethal


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Embryonic Lethal

Ll × Ll


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Embryonic Lethal

Ll × Ll

3 live + 1 dies

(not observed)


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Embryonic Lethal

Ll × Ll

3 live + 1 dies

(not observed)

  • Fertility studies needed to determine the presence of a recessive embryonic lethal.


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Recessive Sex Linked

XLXl × XLY


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Recessive Sex Linked

XLXl × XLY

2 XLX-normal female

1 XLYnormal male

1 XlYdies (not observed)


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Recessive Sex Linked

XLXl × XLY

2 XLX-normal female

1 XLYnormal male

1 XlYdies (not observed)

-- 2:1 sex ratio at birth --


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Embryonic lethals that are associated with other observable phenotypes.


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Embryonic lethals that are associated with other observable phenotypes.

H = hairless dogH > h

h = hair


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Hh × Hh

1 HH + 2Hh + 1hh


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Hh × Hh

1 HH + 2Hh + 1hh

dies

Embryonic lethal, not observed at birth!


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Hh × Hh

1 HH + 2Hh + 1hh

dies

hairless

(all heterozygotes)


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Hh × Hh

1 HH + 2Hh + 1hh

dies

hairless

hair

(all heterozygotes)


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Embryonic lethals that are associated with other observable phenotypes.

2:1 Ratio


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Other Examples

  • White in HORSES

  • Manx tails in CATS

  • Bluefrost coat color in MINK

  • Leg length and size in Dexter CATTLE

  • Creeper (leg length) in CHICKENS

  • Yellow color in MICE


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Multiple Alleles


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Multiple Alleles

  • There are > 2 allelic forms possible at a particular locus segregating in the population.


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Dog Example:

C series in dogs -- C is required for color and cc is albino.


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C Series

C -- color series expressed

c -- albino (pink nose and eyes)

C > c


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Dog Example:

C series in dogs -- C is required for color and cc is albino.

However, other alleles exist that don’t produce the albino phenotype.


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C Series

C -- color series expressed

cch -- chinchilla pattern

cd -- white coat (black nose, dark eyes)

cb-- Cornaz coat (blue eyes), pale gray

c -- albino (pink nose and eyes)

C > cch > cd > cb > c


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cdcd


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cchc × cdcb


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cchc × cdcb

2 cch_ chinchilla

1 cdcwhite

1 cbcCornaz


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Anomalies

  • Incomplete penetrance

  • Phenocopy

  • Variable expressivity


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Incomplete Penetrance


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Incomplete Penetrance

  • Failure of a genotype to be expressed with the phenotype normally associated with it.


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Incomplete Penetrance

  • Stripe marking on forehead of fox.


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Half Stripe

Full Stripe


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SS = full stripe

Ss = half stripe

ss = no stripe

SS × ss


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SS = full stripe

Ss = half stripe

ss = no stripe

SS × ss

Ss (18% no stripe)


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Phenocopy


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Phenocopy

  • An environmental influence causing an effect similar to a phenotype under genetic control.


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Phenocopy

  • An environmental influence causing an effect similar to a phenotype under genetic control.

  • Example -- plant toxins Thalidomide babies


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Variable Expressivity


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Variable Expressivity

  • Variation in phenotypic expression


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Variable Expressivity

  • Variation in phenotypic expression

  • Example -- Mice

  • Dwarfism: Still variations in weights of dwarf mice and may overlap with normal weights


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Anomalies: Callipyge


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GMBT16

BMS2382

OY3, 5, 15

Somewhere in this region

Callipyge

IDVGA30

CSSM18

Ovine Chromosome 18


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Alleles:

C= Callipyge

N = Normal

C

C

N

C

Genotypes:

M

F

M

F

C

N

N

N

M

F

M

F


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CN

NN

X

Callipyge males

Normal females

½CN : ½ N N

M

F

M

F

Expected: 1 callipyge to 1 normal

Actual: 203 callipyge and 209 normal


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NN

CN

X

Normal males

Callipyge females

½NC: ½ N N

M

F

M

F

Expected 1 callipyge : 1 normal

Actual 33 normal


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Polar overdominance

at the callipyge locus

Female callipyge chromosome

(C) “turns off” allele expression

F


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Maternal imprinting:

Maternally-derived allele is silent,

paternally-derived allele is

expressed

Silent allele is reactivated in

paternal germ line


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