Transcript 3.4 Blood Group and sex linked Notes

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