Complex Patterns of Inheritance
description
Transcript of Complex Patterns of Inheritance
Complex Patterns of Inheritance
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.
Law of Independent Assortment: the alleles of different genes separate independently of
one another during gamete formation
I. Sex-linked traits
• A sex-linked trait is a trait whose allele is located on either the X or Y chromosome.
A) Hairy Ears: Gene on the Y Chromosome
B) Most sex-linked traits on X chromosome are recessive
• Examples include: hemophilia, red-green colorblindness, and a form of muscular dystrophy
A person with red-green color blindness sees a number 2
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.
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
Genotypes for Males
• XHY = normal blood clotting
• XhY = male with hemophilia
• Tsarevich Alexei of Russia
had hemophilia
Cross a carrier mother with a normal father.
No daughters with hemophilia, ½ of sons with hemophilia
XH Xh
XH XHXH XHXh
Y XHY XhY
Cross a hemophiliac father with a normal (non-carrier) mother.
All daughers are carriers, no sons have hemophilia.
XH XH
Xh XHXh XHXh
Y XHY XHY
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
Red = RR, White = WW, Pink = RW
Make a Punnett square for a red plant crossed with a white plant
All offspring are pink, with RW genotype
RW RW
RW
RW
R R
W
W
What happens if you cross two pink snapdragons?
Offspring are 1 red, 2 pink, and 1 white
RR RW
RW WW
R W
R
W
1 red (RR), 2 pink (RW), 1 white (WW)
Incomplete
dominance
in horse
coat color
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
• Roan has red and white hairs
Parents
Codominancein chicken feather color.
Black and White feathers
IV. Multiple Alleles• Genes with three or more alleles for a
particular trait.
• Examples are the ABO blood types, fur color in many animals.
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
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
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
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
V. Polygenic traits• Traits that are influenced by 2 or more
genes
• Examples include human height, weight, hair color, eye color, and skin color
Coat color in Labrador retrievers
Coat color in Labrador retrievers
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.
VII. Traits influenced by the environment.
• Color of hydrangea flowers (blue in acidic soil, pink in basic soil)
• Color of arctic fox
• Human height, skin color, behavior