Download 6.3 Chromosomes structure — Further questions Q1. Bk Ch6 S6.3

6.3 Chromosomes structure — Further questions
Q1.
Bk Ch6 S6.3 FQ1
If a heterozygous blood group A person has children with a heterozygous blood group B, what
genotypes may be shown by the offspring? Use a diagram to illustrate your answer.
A1.
Bk Ch6 S6.3 FA1
Alleles A and B are codominant, with allele O being recessive. A Punnett square can be used to
illustrate the genotypes expected when parents with blood types A and B have children.
B
O
A
AB
AO
O
BO
OO
Children of these parents could have any of the following blood groups: AB, A, B or O.
Q2.
Bk Ch6 S6.3 FQ3
The pedigree below shows the inheritance of a type of rickets that is resistant to vitamin D therapy. The
disease is a sex-linked, recessive trait.
a
b
Assign genotypes to the original parents.
What is the genotype of the twin who married? Is it possible that she will have a son who is not
affected or a daughter who is affected? Explain.
A2.
Bk Ch6 S6.3 FA2
N: normal; n: therapy-resistant rickets.
a
Father: XnY; mother: XNXn.
b
XnXn. No. An unaffected son will have the genotype XNY—this mother does not have a dominant
allele to pass on to her sons. An affected daughter will have the genotype XnXn but in this case,
although she will pass on the recessive allele to all of her daughters, the father is normal and
therefore only has a dominant allele on his only X chromosome to pass on to his daughters.
Q3.
Bk Ch6 S6.3 FQ3
Find out what is meant by Y-linked inheritance. Describe the inheritance patterns for Y-linked
inheritance, using specific examples.
Copyright
© Pearson Australia (a division of Pearson Australia Group Pty Ltd)
A3.
Bk Ch6 S6.3 FA3
Y-linked inheritance refers to the inheritance of genes carried on the Y chromosome. The Y
chromosome carries fewer genes than the X chromosome and most of these genes are involved in the
determination of sex and fertility in males. However, there are some other characteristics determined
by genes carried on the Y chromosome. For example, the presence or absence of excessively hairy ears
is a characteristic only passed from father to son and is therefore Y-linked. If a man has the gene for
hairy ears then he will pass this characteristic on to all of his sons since all of his sons receive the Y
chromosome from their father.
Copyright
© Pearson Australia (a division of Pearson Australia Group Pty Ltd)