Inheritance (SL IB Biology)

Identical twins have the same DNA (genotype) but often display many observable physical differences (phenotype). Studies on twins have shown that one twin can be more susceptible to diseases like cancer or diabetes.

Which of the following statements best explains these differences between identical twins?

Which of the following statements about genes is not correct?

Which of the following statements about alleles are correct?

1. New alleles can arise through mutation.
2. There are two different versions, or alleles, of every gene.
3. Every eukaryotic cell contains two alleles of every gene.

Which of the following explains why the father determines the sex of offspring and not the mother?

In humans, there are three alleles that determine blood groups, namely I^O, I^A and I^B. The frequency of the I^O allele in a particular population was found to be 0.72. There was an equal abundance of the remaining two alleles.

What would the frequency of the I^B allele be in this population?

Which row(s) below give(s) correct statements about continuous variation?

Long hair in a species of rabbit is caused by the presence of the allele H^L. These rabbits have either very long hair or moderately long hair. The 'wild-type' short-haired rabbit possesses the allele H^S. The diagram below shows the results of two crosses involving one female and two male rabbits.

Which row of the table below shows the phenotypes of the rabbits with the genotypes H^LH^L and H^LH^S?

A species of plant can have either blue or white flowers. The colour of the flower is controlled by a single gene where the dominant allele codes for blue flowers. 

Two heterozygous plants are crossed; which of the observed outcomes matches up most accurately to the expected ratio of blue to white flowers. 

Two parents have an equal chance of having a child with blood groups A, B, AB, or O.

What are the genotypes of the parents?

A woman is a carrier of haemophilia; her husband does not have haemophilia. 

What are the possible genotypes of their children?

The pedigree diagram shows the inheritance of cystic fibrosis across 3 generations.

Identify the genotype of the individuals labelled 1, 2 and 3 in the pedigree diagram.

A couple are trying to decide whether their children may be at risk of inheriting Huntington's disease. One parent is heterozygous for Huntingtons and the other is a healthy individual. 

Calculate the % chance that their offspring are likely to suffer from the disease.

The pedigree diagram below shows the inheritance of haemophilia across three generations.

Identify the genotype of person Y.

Which of the following statements are true for the determination of sex?

1. The chromosomes inherited through the maternal gametes determine the sex of the offspring
2. Females have a larger quantity of DNA than males
3. Sex is determined by the 23rd pair of chromosomes in humans
4. Sex of an individual can be identified using an image taken of chromosomes during interphase

The pedigree chart below shows the inheritance of Tay-Sachs disease which is an autosomal recessive trait, characterised by neurological problems caused by the death of nerve cells. 

In the pedigree chart, a filled in circle or square means the individual is affected and shows the genetic condition.

What is the probability that individuals 3 and 4 will have another child with Tay-Sachs disease?

Which statements best explain why the ABO blood system in humans is an example of co-dominance?

1. Allele I^A and the allele I^B are both expressed in the heterozygote/AB type blood.
2. Neither allele I^A or the allele I^B can mask the expression of the other allele.
3. There are three alleles of the gene that controls the blood group.
4. There are more than two blood groups.

Two parents with normal factor VIII have a child with haemophilia.

Which is the correct statement?