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. X b Y XBXbXBXb XBXbXBXb XBYXBYXBYXBY X B 0%- 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? X H X h X H Y X H X H X H X h X H Y X h 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 carnationr R R Rr Rr

Results Genotype: 4/4 Rr Phenotype 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 GenotypePhenotype IAIA, IAIOIAIA, IAIO A Blood I B I B, IBI O B Blood IAIBIAIB AB Blood IOIOIOIO 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 IAIBIAIB IOIOIOIO I A I O I B I O IAIOIBIOIAIOIBIO 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  Bbss Figure 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 square BSBsbSbs bs Bs 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:4/16Black/Curly: 6/16  BBSs:2/16Black/Straight: 6/16  Bbss:4/16Brown/ Straight:2/16  BBss: 2/16Brown/Curly: 2/16  bbSs: 2/16  bbss:2/16