Blood Group Notes

IB Assessment Statement

• Describe ABO blood groups as an example of codominance and multiple alleles. Phenotype Genotype O ii A IAIA or IAi B IBIB or IBi AB IAIB

Codominance

• In the cases of some genes, two alleles may be expressed in the phenotype at the same time.

• That is, NO allele is truly dominant or recessive.

Codominance

• When no alleles are dominant in a gene, we say these alleles are codominant.

• Example: If a homozygous white rose (WW) is crossed with a homozygous red rose (RR) all their offspring are pink (WR). That ism they show a blending of physical traits.

Blood Type.

There are three alleles for blood type:• Blood Group B represented by IB

– co-dominant with blood group A– Dominant over blood group O

• Blood Group A represent by IA – co-dominant with blood group B– Dominant over blood group O

• Blood Group O represented by i – Recessive to both group A and B

Practice Cross 1 :

• A person with homozygous Group A blood crosses with a homozygous Group B Blood:

– The Symbols (letters you will use) ______________________

– The Cross (the parent’s genotypes)_________________________

– The Punnett square:

Practice Cross 2:

• A person with heterozygous Group AB blood crosses with another heterozygous Group AB Blood:

• The Symbols (letters you will use) ______________________

• The Cross (the parent’s genotypes)_________________________

• The Punnett square:

Practice Cross 3:

• A person with heterozygous Group AB blood crosses with a person who has O type Blood:

• The Symbols (letters you will use) ______________________

• The Cross (the parent’s genotypes)_________________________

• The Punnett square:

Practice Cross 4:

• A person with heterozygous Group A blood crosses with a person who is heterozygous with B type Blood:

• The Symbols (letters you will use) ______________________

• The Cross (the parent’s genotypes)_________________________

• The Punnett square:

IB Assessment Statement

• Define sex linkage.

IB Assessment Statement

• Describe the inheritance of colour blindness and hemophilia as examples of sex linkage.

– Both colour blindness and hemophilia are produced by a recessive sex-linked allele on the X chromosome.

Sex-Linked Traits Notes

__XX__= FEMALE

___XY__= MALE– There are some traits and genetic disorders

that are carried on the Sex Chromosomes (usually the X)___.

– There are many diseases are on the X chromosome

• Examples:– Hemophilia – Color blindness

• Genetic Disease are usually recessive.

Genotype example

– Examples:

• __XN ___= normal gene

• _ Xn _ = gene with trait or disorder

IB Assessment Statement

– State that a human female can be homozygous or heterozygous with respect to sex-linked genes.

– Explain that female carriers are heterozygous for X-linked recessive alleles.

MALES• Because males only have 1 X chromosome if

they inherit the X chromosome with the disease on it they have the disease because they only have one X chromosomes to hide the trait.

• Thus males inherit sex-linked genetic diseases more frequently than females.

• ___XnY_____= male with trait

• ___XNY__= male without trait

FEMALES

• Inherit 2 X chromosomes_

• Thus, females can also be a Carrier of the trait. This means even if a female does not have a disease, she can pass it to her offspring, if she is a carrier.

–Xn Xn _= female with trait

–XN Xn = female who is a carrier

–XN XN= female without trait

Example problem:

• Colorblindness is a sex-linked trait.

• Cross a carrier female with a normal male.

– Select Symbols:

– Write the cross:

– Make a Punnet Square:

IB Assessment Statement

• Predict the genotypic and phenotypic ratios of offspring of monohybrid crosses involving any of the above patterns of inheritance

• PRACTICE PROBLEMS