Dihybrid Crosses and Different Patterns of Inheritance

Dominant/Recessive Pattern• when two different alleles are present, one

is expressed (dominant) while the other is hidden (recessive)

Dihybrid CrossTwo Trait Punnett Squares

Dihybrid CrossTwo Trait Punnett Squares

• breeding that involves two unique traits– Seed Shape: R = round, r = wrinkled– Seed Color: Y = yellow, y = green

Dihybrid CrossTwo Trait Punnett Squares

Dihybrid CrossTwo Trait Punnett Squares

Dihybrid CrossTwo Trait Punnett Squares

Dihybrid Example• A plant that is heterozygous for seed shape

(Rr) and heterozygous for seed color (Yy) is self-pollinated. What will the genotypic and phenotypic ratios be of the offspring?

Dihybrid Example

Dihybrid Example

RY Ry rY ry

RY

Ry

rY

ry

Dihybrid Example

RY Ry rY ry

RY RRYY RRYy RrYY RrYy

Ry RRYy RRyy RrYy Rryy

rY RrYY RrYy rrYY rrYy

ry RrYy Rryy rrYy rryy

Dihybrid Example

• Genotypic Ratio:– 1 RRYY : 2 RRYy : 1 RRyy : 2 RrYY : 4 RrYy :

2 Rryy : 1 rrYY : 2 rrYy : 1 rryy• Phenotypic Ratio:

– 9 Round & Yellow : 3 Round & Green : 3 Wrinkled & Yellow : 1 Wrinkled & Green

Incomplete dominance• a condition in which a heterozygous

individual appears in-between two different phenotypes– neither allele is completely dominant

• two alleles resulting in three phenotypes

Incomplete dominance• heterozygous individuals have a phenotype

somewhere in the middle of the two alleles• Example in humans

– a straight-haired parent and a curly-haired parent will produce a wavy-haired child

• use an apostrophe (’) or superscript letters to indicate different alleles– S = straight, S’ = curly

• SS = straight, SS’ = wavy, S’S’ = curly

Incomplete dominance

Codominance• two alleles are expressed at the same time• Example in humans

– ABO blood type in humans

Codominance in Shorthorn Cattle

CWCW

CWCR

CRCR

Codominance in Camellia Flowers

CWCW

CWCP

CPCP

Codominance• use superscript letters to show

different alleles–CW = white, CR = red

• CWCW = white, CRCR = red, CWCR = roan

Multiple alleles• genes with 3 or more alleles possible for the

same character• Example in humans

– ABO blood type in humans

Multiple Alleles & Codominance

Multiple alleles• use capital and lowercase letters

and/or superscript letters to show different alleles–TA = __________, TB = __________,

t = __________• TATA = __________, TAt = __________,

TBTB = __________, TBt = __________,

TATB = __________, tt = __________

Multiple alleles• use capital and lowercase letters

and/or superscript letters to show different alleles–TA = type A blood, TB = __________,

t = __________• TATA = __________, TAt = __________,

TBTB = __________, TBt = __________,

TATB = __________, tt = __________

Multiple alleles• use capital and lowercase letters

and/or superscript letters to show different alleles–TA = type A blood, TB = type B blood, t

= __________• TATA = __________, TAt = __________,

TBTB = __________, TBt = __________,

TATB = __________, tt = __________

Multiple alleles• use capital and lowercase letters

and/or superscript letters to show different alleles–TA = type A blood, TB = type B blood, t

= type O blood• TATA = __________, TAt = __________,

TBTB = __________, TBt = __________,

TATB = __________, tt = __________

Multiple alleles• use capital and lowercase letters

and/or superscript letters to show different alleles–TA = type A blood, TB = type B blood, t

= type O blood• TATA = type A blood, TAt = __________,

TBTB = __________, TBt = __________,

TATB = __________, tt = __________

Multiple alleles• use capital and lowercase letters

and/or superscript letters to show different alleles–TA = type A blood, TB = type B blood, t

= type O blood• TATA = type A blood, TAt = type A blood,

TBTB = __________, TBt = __________,

TATB = __________, tt = __________

Multiple alleles• use capital and lowercase letters

and/or superscript letters to show different alleles–TA = type A blood, TB = type B blood, t

= type O blood• TATA = type A blood, TAt = type A blood,

TBTB = type B blood, TBt = __________,

TATB = __________, tt = __________

Multiple alleles• use capital and lowercase letters

and/or superscript letters to show different alleles–TA = type A blood, TB = type B blood, t

= type O blood• TATA = type A blood, TAt = type A blood,

TBTB = type B blood, TBt = type B blood,

TATB = __________, tt = __________

Multiple alleles• use capital and lowercase letters

and/or superscript letters to show different alleles–TA = type A blood, TB = type B blood, t

= type O blood• TATA = type A blood, TAt = type A blood,

TBTB = type B blood, TBt = type B blood,

TATB = type AB blood, tt = __________

Multiple alleles• use capital and lowercase letters

and/or superscript letters to show different alleles–TA = type A blood, TB = type B blood, t

= type O blood• TATA = type A blood, TAt = type A blood,

TBTB = type B blood, TBt = type B blood,

TATB = type AB blood, tt = type O blood

Sex-linked• a trait that is determined by a gene found

on one of the sex chromosomes– many traits are located only on the X

chromosome

Sex-linked• leads to many recessive characteristics

being common in males– males only have one copy of the X chromosome

• Examples in humans– colorblindness, hemophilia (bleeder’s disease)

Sex-linked• must use sex chromosomes as part of

Punnett Square allele identification– Ex: XN = X chromosome with a normal gene,

Xn = X chromosome with a colorblind gene, Y = no gene

Polygenic Inheritance• several genes

influencing one character

• Example in humans:– height, weight, hair

color, and skin color• won’t use a Punnett

Square with this type of inheritance

Environmental influences• conditions around organisms also influence

their phenotype

Environmental influences

Environmental influences

Environmental influences• Examples in humans:

– height and weight are influenced by nutrition