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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

Lecture 4

Continued

Example of Probabilities Using Sex Linkage:

XHY× XHXh

XHXH

XHXh

XHY1/4 normal male

XhY1/4 male with hemophilia

1/2 normal females

Sex

malefemale

normal

hemophilia

Sex

malefemale

normal 1/41/23/4

hemophilia 1/401/4

1/21/2

Conditional Probabilities

• P(affected child) = 1/4

Conditional Probabilities

• P(affected child) = 1/4

• P(hemophilia / male)?

Sex

malefemale

normal 1/41/23/4

hemophilia 1/401/4

1/21/2

Conditional Probabilities

• P(affected child) = 1/4

• P(hemophilia / male) = 1/4 = 1/21/2

Conditional Probabilities

• P(affected child) = 1/4

• P(hemophilia / male) = 1/4 = 1/21/2

• P(hemophilia / female) = 0 = 0 1/2

Lecture 5

Exceptions to Mendel’s Ratios

Sex Influenced

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.

Example of Sex Influence:

Presence of horns in sheep:

Polled -- without horns

Horned -- with horns

Sheep Example:

P = polled

p = horned

Horned malePolled female

pp × PP

Horned male Polled female

pp × PP

All progeny Pp

Horned male Polled female

pp × PP

• All progeny Pp but,

• female -- polled P > p

• male -- horned p > P

malefemale

malefemale

PPPolledPolled

malefemale

PPPolledPolled

ppHornedHorned

malefemale

PPPolledPolled

PpHorned

ppHornedHorned

malefemale

PPPolledPolled

PpHornedPolled

ppHornedHorned

malefemale

PPPolledPolled

PpHornedPolled

ppHornedHorned

p > P

Sex Limited

Sex Limited

• A phenotype that is expressed in only one sex.

Sex Limited

• A phenotype that is expressed in only one sex.

• Examples:

• Antlers -- deer

• Color -- pheasants and cardinals

• Milk production -- dairy

X Inactivation

X Inactivation

T = black hairT = t

t = orange hair

Cat Fanciers’ Association

Cat Fanciers’ Association

PhenotypeGenotype

malefemale

blackXTYXTXT

orange XtYXtXt

PhenotypeGenotype

malefemale

blackXTYXTXT

orange XtYXtXt

tortoiseshellXTXt (unique)

-- calico = tortoiseshell with S_ --

ss XTXt

Cat Fanciers’ Association

S_ XTXt

Cat Fanciers’ Association

• Occasionally a tortoiseshell male happens:

• Occasionally a tortoiseshell male happens:

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

ParentsXTXt × XTY

ParentsXTXt × XTY

GametesXTXt×XT Y

ParentsXTXt × XTY

GametesXTXt×XT Y

Zygotes

• XTXtXTtortoiseshell female

• XTblack female

• Ydies

• XTXtYtortoiseshell male

Non-disjuncture can occur in any chromosome.

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!

(?)

Non-disjuncture can occur in any chromosome.

• trisomic 21 -- Down’s Syndrome

• trisomic 13 -- Patau -- 1/5000

• trisomic 18 -- Edwards -- 1/14000

Lethal Conditions

Lethal Conditions

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

Postnatal Lethal Condition (Abnormalities)

Postnatal Lethal Condition (Abnormalities)

Parrot jaw in cattle:

P = normalP > p

p = parrot jaw

Pp × Pp

Pp × Pp

3 P_ + 1 pp

normal parrot jaw (dies at young age)

Embryonic Lethal

L = normalL > l

l = lethal

Embryonic Lethal

Ll × Ll

Embryonic Lethal

Ll × Ll

3 live + 1 dies

(not observed)

Embryonic Lethal

Ll × Ll

3 live + 1 dies

(not observed)

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

XLXl × XLY

XLXl × XLY

2 XLX-normal female

1 XLYnormal male

1 XlYdies (not observed)

XLXl × XLY

2 XLX-normal female

1 XLYnormal male

1 XlYdies (not observed)

-- 2:1 sex ratio at birth --

Embryonic lethals that are associated with other observable phenotypes.

Embryonic lethals that are associated with other observable phenotypes.

H = hairless dogH > h

h = hair

Hh × Hh

1 HH + 2Hh + 1hh

Hh × Hh

1 HH + 2Hh + 1hh

dies

Embryonic lethal, not observed at birth!

Hh × Hh

1 HH + 2Hh + 1hh

dies

hairless

(all heterozygotes)

Hh × Hh

1 HH + 2Hh + 1hh

dies

hairless

hair

(all heterozygotes)

Embryonic lethals that are associated with other observable phenotypes.

2:1 Ratio

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

Multiple Alleles

Multiple Alleles

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

Dog Example:

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

C Series

C -- color series expressed

c -- albino (pink nose and eyes)

C > c

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.

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

cdcd

cchc × cdcb

cchc × cdcb

2 cch_ chinchilla

1 cdcwhite

1 cbcCornaz

Anomalies

• Incomplete penetrance

• Phenocopy

• Variable expressivity

Incomplete Penetrance

Incomplete Penetrance

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

Incomplete Penetrance

• Stripe marking on forehead of fox.

Half Stripe

Full Stripe

SS = full stripe

Ss = half stripe

ss = no stripe

SS × ss

SS = full stripe

Ss = half stripe

ss = no stripe

SS × ss

Ss (18% no stripe)

Phenocopy

Phenocopy

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

Phenocopy

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

• Example -- plant toxins Thalidomide babies

Variable Expressivity

Variable Expressivity

• Variation in phenotypic expression

Variable Expressivity

• Variation in phenotypic expression

• Example -- Mice

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

Anomalies: Callipyge

GMBT16

BMS2382

OY3, 5, 15

Somewhere in this region

Callipyge

IDVGA30

CSSM18

Ovine Chromosome 18

Alleles:

C= Callipyge

N = Normal

C

C

N

C

Genotypes:

M

F

M

F

C

N

N

N

M

F

M

F

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

NN

CN

X

Normal males

Callipyge females

½NC: ½ N N

M

F

M

F

Expected 1 callipyge : 1 normal

Actual 33 normal

Polar overdominance

at the callipyge locus

Female callipyge chromosome

(C) “turns off” allele expression

F

Maternal imprinting:

Maternally-derived allele is silent,

paternally-derived allele is

expressed

Silent allele is reactivated in

paternal germ line