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“Nature vs. Nurture”Environment and Gene Expression
Gene expression can be affected by many factors, including:
the activity of other genes climate conditions – Ex.: Siamese cat &
Himalayan rabbit fur, flower color in hydrangeas, etc.
“Nature vs. Nurture”Environment and Gene Expression
Gene expression can be affected by many factors, including:
social environment of organism – Ex.: Japanese goby fish changes sex depending on the gender of other fish present
“Nature vs. Nurture”Environment and Gene Expression
Gene expression can be affected by many factors, including:
internal environment of organism – diet (presence of nutrients) affects height; shyness in children is affected by socialization;
External environment of organism – Ex.: Mutagens/carcinogens – cancer development
Refining Mendel’s LawsLinked Genes•Genes located on the same chromosome travel together into the same gamete; •the two traits are inherited together, instead of sorting independently•this is an exception to Mendel’s law of independent assortment.
Intermediate Inheritance:Polygenic TraitsMost traits are polygenic – affected by more than one gene.
Intermediate Inheritance: Incomplete Dominance – “no win”
Result of incomplete dominance: blending of traits in heterozygote
Intermediate Inheritance:Codominance – “win-win”Codominance - both alleles in heterozygote express themselves fully
Ex.: blood types are determined by carbohydrates (sugars) on red blood cells; two alleles two types of carbohydrate molecules on RBCs.
Human blood types also havemultiple alleles (more than two):IA, IB and i (neither)
Rh factor (a different gene) (+, dominant or -, recessive) also determines blood type; ex.: A+, B-, etc.
Blood transfusions - People reject any blood factor they do NOT have.
BB
B A
AA
Phenotype(blood type) Possible
genotype(s)Antigen on
RBCAntibody in
PlasmaCan Donate
to Blood Types
A
B
AB
O
AA or AO
BB or BO
Anti-B
Anti-A
Anti-A Anti-B
A and AB
B and AB
AB
OO
None AB
All Blood Types
A
A
A
B
BB
ABABA
B
Sex-Linked Traits
&
Sex-Influenced Traits
* Add the missing examples
to your notes. *
Which sex has more chromosomes?
Which sex has more genes?
It starts at a young age and men just get worseBut wait! Things are not as bad as they seem…
X Inactivation( A.K.A. Revenge for
Boys! ) Early in embryonic development in females, one of the two X
chromosomes is randomly and permanently inactivated in cells other than egg cells.
This ensures that females, like males, have one functional copy of the X chromosome in each body cell.
Some genes on the X chromosome escape X-inactivation. Many of these genes are located at the ends of each arm of the X chromosome in areas known as the pseudoautosomal regions.
Although many genes are unique to the X chromosome, genes in the pseudoautosomal regions are present on both sex chromosomes, and many are essential for normal development.
Tortoiseshell / Calico CatPrimary gene for coat color on the X chromosome has two co-dominant alleles,Orange (XO) & Black (XB)
X inactivation (random) in different embryonic cells (melanocytes) produces the pattern
Delayed melanocyte migration during development (another gene does this) creates white in the three-color cats (cells w/o pigment)
Male or female?Females, except for rare XXY males
Early embryo
X chromosomes
Allele fororange fur
Allele forblack fur
Cell divisionand random
X chromosomeinactivation
Two cell populationsin adult
Active X
Inactive X
Inactive X
Active X
Orangefur
Black fur
Figure 11.5
Sex-Linked Traits
Colorblindness
Hemophilia
Linked to X chromosome, are recessive
Sex-Linked TraitsSex-linked traits are encoded by genes on the X or Y chromosomes.
Ex.: Hemophilia, a defect in blood clotting, is a recessive, X-linked trait (Xh) found mostly in boys.
Mom(carrier)
Dad
XH Y
XHXHXH
girlXHYboy
XhXHXh
girlXhYBoy*
* Since the Y chromosome does not have the gene for the blood clotting factor, this boy has no good copy of the gene and has the recessive phenotype.
Hairy PinnaLinked to
Y chromosome
Sex Influenced Trait
Gene is on an Autosome (#1 - #22), but the Phenotype is INFLUENCED by the SEX HORMONES which are controlled by the SEX CHROMOSOMES
Sex Influenced Traits
Male Patterned Baldness
Sex Influenced Trait
Male Female
Phenotype Phenotype
BB
B’B
B’B’
Hair Hair
HairPatterned Baldness
Patterned Baldness
Patterned Baldness