Genetics Beyond Mendel. Incomplete Dominance Phenotype is a blend of the alleles An intermediate is seen Four o’clocks Homozygous Red Heterozygous Homozygous

Genetics Beyond MendelGenetics Beyond Mendel

Incomplete DominanceIncomplete DominancePhenotype is a blend of the alleles

An intermediate is seen

Four o’clocks

Homozygous Red Heterozygous Homozygous White

Sometimes written: C and C1

Incomplete Dominance - HumansIncomplete Dominance - Humans

Hair FolliclesHair Follicles– Curly hair is homozygous recessiveCurly hair is homozygous recessive– Straight hair is homozygous Straight hair is homozygous

dominantdominant– Heterozygous individuals have Heterozygous individuals have

wavy hairwavy hair

Incomplete Dominance - HumansIncomplete Dominance - Humans

Cholesterol GeneCholesterol Gene– Homozygous Homozygous

dominant – Very dominant – Very high cholesterolhigh cholesterol

– Heterozygous – Heterozygous – high cholesterolhigh cholesterol

– Homozygous Homozygous recessive – normal recessive – normal cholesterolcholesterol

Multiple Allele TraitsMultiple Allele Traits

More than two alleles for a traitMore than two alleles for a trait

Only two forms are inheritedOnly two forms are inherited

Can have co-dominance Can have co-dominance

Can have a hierarchy of dominanceCan have a hierarchy of dominance– hair color in mice determined by a single gene hair color in mice determined by a single gene

with alleles for black, brown, agouti, gray, with alleles for black, brown, agouti, gray, albinoalbino

agouti > black > brown > albino. agouti > black > brown > albino.

CodominanceCodominance

Both alleles are expressed Both alleles are expressed at the same timeat the same time

Roan horse appears grey but has a mixture of white and black hairs

Hybrid camellia

Blood TypesBlood Types

Multiple Alleles (3) and Co dominantMultiple Alleles (3) and Co dominantA, B, O alleles produce:A, B, O alleles produce:

AA = AAA = A BB = BBB = B

AO = AAO = A BO = BBO = B

AB = ABAB = AB OO = OOO = O

Four blood type phenotypesFour blood type phenotypes

Sometimes written ISometimes written IAA I IBB i i

Polygenic InheritancePolygenic Inheritance

More than one set of More than one set of alleles controls a traitalleles controls a trait

Skin color has three Skin color has three different setsdifferent sets

Effect is additiveEffect is additive

Environment and InheritanceEnvironment and Inheritance

Gene expression is influenced by the Gene expression is influenced by the environmentenvironment

Chemicals, temperature, pH levels, radiation, Chemicals, temperature, pH levels, radiation, nutrition can all be factorsnutrition can all be factors

Himalayan rabbits – fur changes color with exposure to cold

Turtles Turtles – Sex determined by temperature of eggs Sex determined by temperature of eggs – Males produced at lower incubation Males produced at lower incubation

temperatures than females temperatures than females – At temperatures around 30 degrees Celsius At temperatures around 30 degrees Celsius

only female turtles ariseonly female turtles arise

Lizards and crocodiliansLizards and crocodilians– Females produced at lower temperatures, Females produced at lower temperatures,

males at higher temperatures males at higher temperatures

Environment and InheritanceEnvironment and Inheritance

Gender InheritanceGender Inheritance

Due to one set of Due to one set of chromosomes in chromosomes in humanshumansXX = female XX = female XY = MaleXY = MaleOne X must come from One X must come from mothermotherSperm can donate an X Sperm can donate an X or Yor YSex is determined at Sex is determined at fertilization fertilization

Sex-linked InheritanceSex-linked InheritanceSex linked traits:– Genes that are carried by either sex chromosome– Y linked genes appear on Y chromosome– X linked genes appear on the X chromosome

Only men inherit Y chromosomes– Only ones to inherit Y-linked traits

Men and women both inherit X chromosomes– Both can get the X-linked traits

Males –

Genes on the X chromosome that do not code for gender are expressed

Even recessive genes

No corresponding gene on the Y chromosome.

Sex-linked InheritanceSex-linked Inheritance

Females –

Recessive allele on one X chromosome is masked by a dominant allele on the other

Women are frequently carriers of X-linked traits but rarely have them expressed in their own phenotypes.


Sex-linked InheritanceSex-linked InheritanceX chromosome carries coat pigment genes

One X chromosome randomly becomes deactivated.

The active X chromosome determines the color in that particular cell

A human female "carrier“ heterozygous for sex-linked trait causing red-green color blindness

(recessive) marries a normal male

What proportion of their male progeny will have red-green color blindness?


Genotype of parentsGenotype of parentsMother: heterozygous for red green color blindness

Father: homozygous dominant on X no allele on Y

½ of the daughters

are carriers

½ of the daughters

are normal

½ of the sons are

color blind

½ of the sons are normal

The two most noted X linked genetic disorders are hemophilia and color blindness

Pedigree DiagramPedigree Diagram

Visual chart of a family’s genetic historyVisual chart of a family’s genetic history




Documents

Genetics Beyond Mendel. Incomplete Dominance Phenotype is a blend of the alleles An intermediate is seen Four o’clocks Homozygous Red Heterozygous Homozygous