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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 Y 1/4 normal male X h Y 1/4 male with hemophilia. 1/2 normal females. Sex male female normal hemophilia . Sex male female

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slide2

Lecture 4

Continued

slide3

Example of Probabilities Using Sex Linkage:

XHY × XHXh

XHXH

XHXh

XHY 1/4 normal male

XhY 1/4 male with hemophilia

1/2 normal females

slide4

Sex

male female

normal

hemophilia

slide5

Sex

male female

normal 1/4 1/2 3/4

hemophilia 1/4 0 1/4

1/2 1/2

slide6

Conditional Probabilities

  • P(affected child) = 1/4
slide7

Conditional Probabilities

  • P(affected child) = 1/4
  • P(hemophilia / male)?
slide8

Sex

male female

normal 1/4 1/2 3/4

hemophilia 1/4 0 1/4

1/2 1/2

slide9

Conditional Probabilities

  • P(affected child) = 1/4
  • P(hemophilia / male) = 1/4 = 1/2 1/2
slide10

Conditional Probabilities

  • P(affected child) = 1/4
  • P(hemophilia / male) = 1/4 = 1/2 1/2
  • P(hemophilia / female) = 0 = 0 1/2
slide11

Lecture 5

Exceptions to Mendel’s Ratios

slide13

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.
slide14

Example of Sex Influence:

Presence of horns in sheep:

Polled -- without horns

Horned -- with horns

slide15

Sheep Example:

P = polled

p = horned

slide17

Horned male Polled female

pp × PP

All progeny Pp

slide18

Horned male Polled female

pp × PP

  • All progeny Pp but,
  • female -- polled P > p
  • male -- horned p > P
slide20

male female

PP Polled Polled

slide21

male female

PP Polled Polled

pp Horned Horned

slide22

male female

PP Polled Polled

PpHorned

pp Horned Horned

slide23

male female

PP Polled Polled

Pp Horned Polled

pp Horned Horned

slide24

male female

PP Polled Polled

Pp Horned Polled

pp Horned Horned

p > P

slide26

Sex Limited

  • A phenotype that is expressed in only one sex.
slide27

Sex Limited

  • A phenotype that is expressed in only one sex.
  • Examples:
  • Antlers -- deer
  • Color -- pheasants and cardinals
  • Milk production -- dairy
slide29

X Inactivation

In a sex-linked locus:

slide30

X Inactivation

In a sex-linked locus:

T = black hair T = t

t = orange hair

slide33

PhenotypeGenotype

male female

black XTY XTXT

orange XtY XtXt

slide34

PhenotypeGenotype

male female

black XTY XTXT

orange XtY XtXt

tortoiseshell XTXt (unique)

-- calico = tortoiseshell with S_ --

slide35

ss XTXt

Cat Fanciers’ Association

slide36

S_ XTXt

Cat Fanciers’ Association

slide38

Occasionally a tortoiseshell male happens:

  • Nondisjuncture -- failure of chromosomes to separate properly during meiosis
slide40

Parents XTXt × XTY

Gametes XTXt× XT Y

slide41

Parents XTXt × XTY

Gametes XTXt× XT Y

Zygotes

  • XTXtXT tortoiseshell female
  • XT black female
  • Y dies
  • XTXtY tortoiseshell male
slide43

Non-disjuncture can occur in any chromosome.

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

Maternal age Incidence/1000

 25 0.5

30 1.0

35 6.0

40 12.0

 45 21.0

Not near as dramatic in males!

(?)

slide44

Non-disjuncture can occur in any chromosome.

  • trisomic 21 -- Down’s Syndrome
  • trisomic 13 -- Patau -- 1/5000
  • trisomic 18 -- Edwards -- 1/14000
slide46

Lethal Conditions

  • Gene or genotype that leads to the death of the individual.
slide48

Postnatal Lethal Condition (Abnormalities)

Parrot jaw in cattle:

P = normal P > p

p = parrot jaw

slide50

Pp × Pp

3 P_ + 1 pp

normal parrot jaw (dies at young age)

slide51

Embryonic Lethal

L = normal L > l

l = lethal

slide53

Embryonic Lethal

Ll × Ll

3 live + 1 dies

(not observed)

slide54

Embryonic Lethal

Ll × Ll

3 live + 1 dies

(not observed)

  • Fertility studies needed to determine the presence of a recessive embryonic lethal.
slide56

Recessive Sex Linked

XLXl × XLY

2 XLX- normal female

1 XLY normal male

1 XlY dies (not observed)

slide57

Recessive Sex Linked

XLXl × XLY

2 XLX- normal female

1 XLY normal male

1 XlY dies (not observed)

-- 2:1 sex ratio at birth --

slide59

Embryonic lethals that are associated with other observable phenotypes.

H = hairless dog H > h

h = hair

slide61

Hh × Hh

1 HH + 2Hh + 1hh

slide62

Hh × Hh

1 HH + 2Hh + 1hh

dies

Embryonic lethal, not observed at birth!

slide63

Hh × Hh

1 HH + 2Hh + 1hh

dies

hairless

(all heterozygotes)

slide64

Hh × Hh

1 HH + 2Hh + 1hh

dies

hairless

hair

(all heterozygotes)

slide66

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
slide68

Multiple Alleles

  • There are > 2 allelic forms possible at a particular locus segregating in the population.
slide69

Dog Example:

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

slide70

C Series

C -- color series expressed

c -- albino (pink nose and eyes)

C > c

slide71

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.

slide72

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

slide75

cchc × cdcb

2 cch_ chinchilla

1 cdc white

1 cbc Cornaz

slide76

Anomalies

  • Incomplete penetrance
  • Phenocopy
  • Variable expressivity
slide78

Incomplete Penetrance

  • Failure of a genotype to be expressed with the phenotype normally associated with it.
slide79

Incomplete Penetrance

  • Stripe marking on forehead of fox.
slide80

Half Stripe

Full Stripe

slide81

SS = full stripe

Ss = half stripe

ss = no stripe

SS × ss

slide82

SS = full stripe

Ss = half stripe

ss = no stripe

SS × ss

Ss (18% no stripe)

slide84

Phenocopy

  • An environmental influence causing an effect similar to a phenotype under genetic control.
slide85

Phenocopy

  • An environmental influence causing an effect similar to a phenotype under genetic control.
  • Example -- plant toxins Thalidomide babies
slide87

Variable Expressivity

  • Variation in phenotypic expression
slide88

Variable Expressivity

  • Variation in phenotypic expression
  • Example -- Mice
  • Dwarfism: Still variations in weights of dwarf mice and may overlap with normal weights
slide91

GMBT16

BMS2382

OY3, 5, 15

Somewhere in this region

Callipyge

IDVGA30

CSSM18

Ovine Chromosome 18

slide92

Alleles:

C= Callipyge

N = Normal

C

C

N

C

Genotypes:

M

F

M

F

C

N

N

N

M

F

M

F

slide93

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

slide94

NN

CN

X

Normal males

Callipyge females

½NC: ½ N N

M

F

M

F

Expected 1 callipyge : 1 normal

Actual 33 normal

slide95

Polar overdominance

at the callipyge locus

Female callipyge chromosome

(C) “turns off” allele expression

F

slide96

Maternal imprinting:

Maternally-derived allele is silent,

paternally-derived allele is

expressed

Silent allele is reactivated in

paternal germ line

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