Unit 4 – Lecture 7

Review Mendellian / Single-Gene Inheritance

two alleles per gene = 1 dominant, 1 recessive

ex: R = red, r = blueRR = redRr = redrr = blue

COLOR THE IMAGES ON YOUR LECTURE NOTES

Discuss

What does it mean to be “incomplete” ?[don’t say – to not be complete…think about

this]

Incomplete DominanceIncomplete Dominance

two dominant alleles present BLEND of alleles is expressed when

combineduses same letter with “prime” or

another letter as exponentcan have a recessive allele still – which is

hidden by BOTH of the dominant alleles if present.

A 1

Incomplete Dominance – cont’dIncomplete Dominance

ex: R = red, R1 = blueRR = redRR1 = PURPLER1R1 = blue

COLOR THE IMAGES ON YOUR LECTURE NOTES

CodominanceCodominance

two dominant alleles presentBOTH alleles are expressed when combinedoffspring show both phenotypes at same timeuses same letter with “prime” or

another letter as exponentcan have a recessive allele still – which is

hidden by BOTH of the dominant alleles if present.

Codominance – cont’d Codominance

ex: R = red, R1 = blueRR = redRR1 = red AND blue

[striped, spotted, checkered, etc]R1R1 = blue

COLOR THE IMAGES ON YOUR LECTURE NOTES

Multiple AllelesMultiple Alleles

trait is coded for by more than 2 alleles for the SAME gene [same letter!!]

more combinations for the same traitgene can have:

multiple dominant alleles – like codominant or incomplete dominance

multiple recessive alleles – all of which would be hidden by any dominant allele present

MA Example - DiscussExample: three alleles for the “R” geneR = red R1 = white r = orange

What color phenotypes would result from each of the following genotypes? [assume co-dominance]

RR RR1 R1R1 RrR1r rr

redwhitewhite

red AND whiteredorange

Multiple Alleles – cont’dMultiple Alleles

ex: Blood Type – codominant multiple allele traitalleles = IA, IB & io

A and B are dominant, O is recessive

caps letter “I” lower-case letter “i”

MA – Discuss So…if A [IA] and B [IB] are dominant,

and O [io]is recessive …which genotypes will give each blood-type

phenotype? [A, B, and O]

A blood: IA IA or IA io

B blood: IB IB or IB io

O blood: only io io

NOTE

You MAY NOT do blood type as your multiple allele trait.

Your traits must ALL be able to be seen just by looking at your creature.

Polygene InheritancePolygene Inheritance

“poly” = manytraits are influenced by many genes

will have combinations of different lettersex: traits with ranges or many types

hair/eye/skin color, height, build, etc.

Polygene InheritancePolygene Inheritance

ex: A / G / R = red a / g / r = no redmore dominant alleles, more colorAa Gg Rr is darker red than Aa gg rr

Naming InheritanceTypes of Chromosomes

Autosome = non-sex determining chromosome [1-22]“autosomal” trait =

trait on a non-sex chromosomeSex-Chromosome = X or Y,

chromosome pair #23“sex-linked” trait =

trait on the X or Y [sex] chromosome

Naming InheritanceAutosomal Dominant

dominant trait on a non-sex chromosomeheterozygotes [Aa] and

dominant homozygotes [AA] have the traitchildren with trait have at least

one parent with the traitaffects males and females equally

Naming InheritanceAutosomal Recessive

recessive trait on a non-sex chromosomemust be recessive homozygote [aa] to have the

traitchildren with trait have parents who either

show or carry the traitcarrier – heterozygote person for a recessive

trait – does not show it, but has the allele [Aa]if both parents have the trait,

ALL children will have the trait

Naming InheritanceAutosomal Recessive

affects males and females equallytraits often skip generations

Naming InheritanceSex-linked Dominant [XA]

dominant trait on a sex chromosome typically on the X-chromosome many are fatal [especially in males]if both parents have trait, most children will

have it¾ of children if heterozygous motherall children if homozygous mother

affects males and females equallyif both parents have it, all kids have it.

Naming InheritanceSex-linked Recessive [Xa]

recessive trait on a sex-chromosometypically on the X-chromosome females can be carriers; males cannotaffects more males than females

son with trait can have parents who don’t show trait

no father to son transmission of traittraits often skip generations