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Complex Patterns of Inheritance

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Page 1: Complex Patterns of Inheritance. Mendel’s Laws Law of Segregation: Organisms inherit two copies of each gene, one from each parent Organisms donate only

Complex Patterns of Inheritance

Page 2: Complex Patterns of Inheritance. Mendel’s Laws Law of Segregation: Organisms inherit two copies of each gene, one from each parent Organisms donate only

Mendel’s Laws

Law of Segregation:

• Organisms inherit two copies of each gene, one from each parent

• Organisms donate only one copy of each gene in their gametes. Thus, the two copies of each gene segregate, or separate, during gamete formation.

Page 3: Complex Patterns of Inheritance. Mendel’s Laws Law of Segregation: Organisms inherit two copies of each gene, one from each parent Organisms donate only
Page 4: Complex Patterns of Inheritance. Mendel’s Laws Law of Segregation: Organisms inherit two copies of each gene, one from each parent Organisms donate only

Law of Independent Assortment: the alleles of different genes separate independently of

one another during gamete formation

Page 5: Complex Patterns of Inheritance. Mendel’s Laws Law of Segregation: Organisms inherit two copies of each gene, one from each parent Organisms donate only

I. Sex-linked traits

• A sex-linked trait is a trait whose allele is located on either the X or Y chromosome.

Page 6: Complex Patterns of Inheritance. Mendel’s Laws Law of Segregation: Organisms inherit two copies of each gene, one from each parent Organisms donate only

A) Hairy Ears: Gene on the Y Chromosome

Page 7: Complex Patterns of Inheritance. Mendel’s Laws Law of Segregation: Organisms inherit two copies of each gene, one from each parent Organisms donate only

B) Most sex-linked traits on X chromosome are recessive

• Examples include: hemophilia, red-green colorblindness, and a form of muscular dystrophy

Page 8: Complex Patterns of Inheritance. Mendel’s Laws Law of Segregation: Organisms inherit two copies of each gene, one from each parent Organisms donate only

A person with red-green color blindness sees a number 2

Page 9: Complex Patterns of Inheritance. Mendel’s Laws Law of Segregation: Organisms inherit two copies of each gene, one from each parent Organisms donate only
Page 10: Complex Patterns of Inheritance. Mendel’s Laws Law of Segregation: Organisms inherit two copies of each gene, one from each parent Organisms donate only

Hemophilia• In this pedigree, only males are affected, and sons

do not share the phenotypes of their fathers.– Thus, hemophilia is linked to a sex chromosome–the X.

• Expression of hemophilia often skips generations.– Thus, it is recessive.

Extensive bruising of

the left forearm

and hand in a patient

with hemophilia.

Page 11: Complex Patterns of Inheritance. Mendel’s Laws Law of Segregation: Organisms inherit two copies of each gene, one from each parent Organisms donate only

Genotypes for females

XHXH = normal blood clotting, non-carrier

XHXh = normal blood clotting, carrier of gene

XhXh = female with hemophilia

Queen Victoria of the

United Kingdom was a

carrier of hemophilia

Page 12: Complex Patterns of Inheritance. Mendel’s Laws Law of Segregation: Organisms inherit two copies of each gene, one from each parent Organisms donate only
Page 13: Complex Patterns of Inheritance. Mendel’s Laws Law of Segregation: Organisms inherit two copies of each gene, one from each parent Organisms donate only

Genotypes for Males

• XHY = normal blood clotting

• XhY = male with hemophilia

• Tsarevich Alexei of Russia

had hemophilia

Page 14: Complex Patterns of Inheritance. Mendel’s Laws Law of Segregation: Organisms inherit two copies of each gene, one from each parent Organisms donate only

Cross a carrier mother with a normal father.

Page 15: Complex Patterns of Inheritance. Mendel’s Laws Law of Segregation: Organisms inherit two copies of each gene, one from each parent Organisms donate only

No daughters with hemophilia, ½ of sons with hemophilia

XH Xh

XH XHXH XHXh

Y XHY XhY

Page 16: Complex Patterns of Inheritance. Mendel’s Laws Law of Segregation: Organisms inherit two copies of each gene, one from each parent Organisms donate only

Cross a hemophiliac father with a normal (non-carrier) mother.

Page 17: Complex Patterns of Inheritance. Mendel’s Laws Law of Segregation: Organisms inherit two copies of each gene, one from each parent Organisms donate only

All daughers are carriers, no sons have hemophilia.

XH XH

Xh XHXh XHXh

Y XHY XHY

Page 18: Complex Patterns of Inheritance. Mendel’s Laws Law of Segregation: Organisms inherit two copies of each gene, one from each parent Organisms donate only
Page 19: Complex Patterns of Inheritance. Mendel’s Laws Law of Segregation: Organisms inherit two copies of each gene, one from each parent Organisms donate only
Page 20: Complex Patterns of Inheritance. Mendel’s Laws Law of Segregation: Organisms inherit two copies of each gene, one from each parent Organisms donate only

II. Incomplete Dominance• An individual displays a trait that is

intermediate between the two parents

• Example: a red snapdragon

crossed with a white

snapdragon produces

pink offspring

Page 21: Complex Patterns of Inheritance. Mendel’s Laws Law of Segregation: Organisms inherit two copies of each gene, one from each parent Organisms donate only

Red = RR, White = WW, Pink = RW

Page 22: Complex Patterns of Inheritance. Mendel’s Laws Law of Segregation: Organisms inherit two copies of each gene, one from each parent Organisms donate only

Make a Punnett square for a red plant crossed with a white plant

Page 23: Complex Patterns of Inheritance. Mendel’s Laws Law of Segregation: Organisms inherit two copies of each gene, one from each parent Organisms donate only

All offspring are pink, with RW genotype

RW RW

RW

RW

R R

W

W

Page 24: Complex Patterns of Inheritance. Mendel’s Laws Law of Segregation: Organisms inherit two copies of each gene, one from each parent Organisms donate only

What happens if you cross two pink snapdragons?

Page 25: Complex Patterns of Inheritance. Mendel’s Laws Law of Segregation: Organisms inherit two copies of each gene, one from each parent Organisms donate only

Offspring are 1 red, 2 pink, and 1 white

RR RW

RW WW

R W

R

W

Page 26: Complex Patterns of Inheritance. Mendel’s Laws Law of Segregation: Organisms inherit two copies of each gene, one from each parent Organisms donate only

1 red (RR), 2 pink (RW), 1 white (WW)

Page 27: Complex Patterns of Inheritance. Mendel’s Laws Law of Segregation: Organisms inherit two copies of each gene, one from each parent Organisms donate only

Incomplete

dominance

in horse

coat color

Page 28: Complex Patterns of Inheritance. Mendel’s Laws Law of Segregation: Organisms inherit two copies of each gene, one from each parent Organisms donate only

III. Codominance

• Two dominant alleles are expressed at the same time

• Roan coat color in horses or cows is an example

• A roan horse has both red and white hairs

Page 31: Complex Patterns of Inheritance. Mendel’s Laws Law of Segregation: Organisms inherit two copies of each gene, one from each parent Organisms donate only

IV. Multiple Alleles• Genes with three or more alleles for a

particular trait.

• Examples are the ABO blood types, fur color in many animals.

Page 32: Complex Patterns of Inheritance. Mendel’s Laws Law of Segregation: Organisms inherit two copies of each gene, one from each parent Organisms donate only

Coat color in rabbitsPhenotype Allele Pattern of

Inheritance

Dark gray coat C Dominant to all other alleles

Chinchilla (silver-gray)

cch Dominant to Himalayan and white

Himalayan

(white with dark ears)

ch

Dominant to white

White c recessive

Page 33: Complex Patterns of Inheritance. Mendel’s Laws Law of Segregation: Organisms inherit two copies of each gene, one from each parent Organisms donate only

1. List all possible genotypes for a: a) dark gray-coated rabbit CC, Ccch, Cch, Cc b) chinchilla rabbit cchcch, cchch, cchc c) Himalayan rabbit chch, chc d) white rabbit cc

Page 34: Complex Patterns of Inheritance. Mendel’s Laws Law of Segregation: Organisms inherit two copies of each gene, one from each parent Organisms donate only

2. Predict the phenotype for a rabbit with a chcch genotype

chinchilla

Predict the phenotype for a rabbit with a Cch genotype

dark gray

3. Would it be possible to obtain white rabbits if one parent is white and the other is chinchilla?

Yes, if the chinchilla parent has a white allele

Page 35: Complex Patterns of Inheritance. Mendel’s Laws Law of Segregation: Organisms inherit two copies of each gene, one from each parent Organisms donate only

4. Would it be possible to obtain chinchilla rabbits if one parent is Himalayan and the other is white?

No, because chinchilla is dominant to both Himalayan and white, so the allele couldn’t be “hiding”.

5. A chinchilla rabbit is mated with a Himalayan. Some offspring are white. What are the parents’ genotypes?

Himalayan is chc and chinchilla parent is cchc

Page 36: Complex Patterns of Inheritance. Mendel’s Laws Law of Segregation: Organisms inherit two copies of each gene, one from each parent Organisms donate only

V. Polygenic traits• Traits that are influenced by 2 or more

genes

• Examples include human height, weight, hair color, eye color, and skin color

Page 37: Complex Patterns of Inheritance. Mendel’s Laws Law of Segregation: Organisms inherit two copies of each gene, one from each parent Organisms donate only
Page 38: Complex Patterns of Inheritance. Mendel’s Laws Law of Segregation: Organisms inherit two copies of each gene, one from each parent Organisms donate only
Page 39: Complex Patterns of Inheritance. Mendel’s Laws Law of Segregation: Organisms inherit two copies of each gene, one from each parent Organisms donate only

Coat color in Labrador retrievers

Page 40: Complex Patterns of Inheritance. Mendel’s Laws Law of Segregation: Organisms inherit two copies of each gene, one from each parent Organisms donate only

Coat color in Labrador retrievers

Page 41: Complex Patterns of Inheritance. Mendel’s Laws Law of Segregation: Organisms inherit two copies of each gene, one from each parent Organisms donate only

VI. Epistasis

• One gene that interferes with the expression of other genes.

• Example is with albinism.

• One gene interferes with all other genes for pigment production.

Page 42: Complex Patterns of Inheritance. Mendel’s Laws Law of Segregation: Organisms inherit two copies of each gene, one from each parent Organisms donate only

VII. Traits influenced by the environment.

• Color of hydrangea flowers (blue in acidic soil, pink in basic soil)

Page 43: Complex Patterns of Inheritance. Mendel’s Laws Law of Segregation: Organisms inherit two copies of each gene, one from each parent Organisms donate only

• Color of arctic fox

• Human height, skin color, behavior