“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