Different Types of Inheritance

SEX LINKED TRAITS

First Type of Inheritance

Sex Determination

In humans and many other organisms, sex is determined by the X and Y chromosomes.

Females: XX

Males: XY

Sex Determination

Sons get their X chromosome from their mothers only.

Fathers must pass their X chromosomes to their daughters.

Sex Linked Traits

Genes that are found on the X chromosome follow a have a special pattern of inheritance:

X linked traits are only passed to sons from the mother

Males are much more likely to be affected than females. If trait is recessive, daughters have a second X

chromosome so they can be heterozygous. Sons only have one X chromosome

Sex Linked Traits

Daughters can be carriers and pass the trait onto their son.

Examples

Baldness

Example: Colorblindness

Sex Linked Problem

A woman is not colorblind but her husband is. Construct a punnett square to determine what is the chance that their children will be colorblind.

Xb

Y

XBXb XBXb

XBY XBY

XB XB0%- what about % of being carrier

50%

Sex Linked Example

A woman who is a carrier for hemophilia marries an unaffected male. What is the % chance that their children will be affected?

XH Xh

XH

Y

XH XH XH Xh

XH Y Xh Y

25% affected- how many carriers?

25%

INCOMPLETE DOMINANCE

Second Type of Inheritance:

Incomplete Dominance

Inheritance that occurs when one trait is not completely dominant over another

Results in the heterozygous form being blended together

Solving an Incomplete Dominance Problem

Perform a regular monohybrid punnett square

Only difference is the heterozygous offspring will be mixture of two traits (i.e. if black and white than gray)

Example

Red carnations are not completely dominant to white carnations- perform a punnett square mating a red and white carnation

r r

R

R

Rr

Rr

Rr

Rr

Results

Genotype: 4/4 RrPhenotype 4/4 Pink

Example: Black fur (B) is dominant over white fur (b) in guinea pigs. Cross a grey guinea pig with a white guinea. What do we get?

Answer: ½ Bb (grey) and ½ bb (white)

CODOMINANCE

Third Type of Inheritance

Codominance

When two different alleles are present and both are expressed

Codominance Example

Red flowers and white flowers are codominant.

What color will the heterozygote be?

Cross a red flower with a white flower and report the phenotype and genotype.

Example: Blood Types

Red blood cells are coated with different markers.

Each person contains either A, B, A and B

or neither protein.

Blood Types are: A, B, AB, O

Blood Type Key

Genotype Phenotype

IAIA, IAIO A Blood

IBIB, IBIO B Blood

IAIB AB Blood

IOIO O Blood

Example: Blood Type

Susan (blood type AB) and Bryan (blood type O) have a son that has blood type B? Since neither Susan nor Bryan have this blood type, was their a mistake in the hospital?

Construct punnett square on next slide

Example: Blood Types

IA IB

IO

IO

IA IO IBIO

IAIO IBIO

Results: ½ A blood type or ½ blood type B

Yes he is their son!

DIHYBRID CROSSES

Fourth Type of Inheritance:

Dihybrid Crosses

Cross that involves two traits

Concludes with 16 offspring

Steps for Solve for Dihybrid Cross

Make a key for the two traits that you are crossing Black Hair (B) vs Brown Hair (b) Curly Hair (S) vs Straight Hair (s)

Write out the different genotypes of the parents Mother is heterozygous for both traits BbSs Father is heterozygous for hair color but has straight hair

BbssFigure out the possible gametes (similar to FOIL)

there are four for each parent and each gamete must have one allele from each trait Mother: BbSs BS; Bs; bS; bs Father: Bbss Bs; Bs; bs;bs

Steps for Solve for Dihybrid Cross

Set up your punnett squareBS Bs bS bs

bs

bs

Bs

Bs

BbSs

BbSs

BBSs

BBSs

Bbss

Bbss

BBss

BBss

bbSs

bbSs

BbSs

BbSs

bbss

bbss

Bbss

Bbss

Steps for Solve for Dihybrid Cross

Count up the possible genotypes and phenotypes that you have from your punnett square Genotypes: Phenotypes:

BbSs:4/16 Black/Curly: 6/16 BBSs:2/16 Black/Straight: 6/16 Bbss:4/16 Brown/ Straight:2/16 BBss: 2/16 Brown/Curly: 2/16 bbSs: 2/16 bbss:2/16