Inheritance PPQs #1

State what is meant by the term gene

Sequence of bases in DNA coding for a sequence of amino acids

Two parents who are both heterozygous for the mutated allele are expecting a child. Use a generic diagram to determine the probability of this child being homozygous for the mutated allele.

25%

Explain how a change of one amino acid could lead to a change in the structure of the haemoglobin protein.

Different primary structure

So different R group

Secondary structure will change

Due to change in hydrogen bonding

Haemoglobin may not bond to oxygen

Even though both offspring are from the same father and mother they may be genetically different. Explain why.

Zygote is from different gametes

Each gamete contains different combination of alleles

Due to independent assortment during meiosis

During fertilisation, only one sperm can fertilise the egg cell. Explain why a second sperm cannot fertilise the egg cell.

Fusion of cortical granules with egg cell membrane

Results in hardening of zona pellucida

Therefore sperm cells cannot reach egg cell membrane

Explain what is meant by the term sex-linked disorder

A disorder caused by a mutated gene

Located on the X chromosome

Therefore the disorder is more likely in female than male

Explain why the genotype frequency for males with DMD (a sex-linked disorder) cannot be calculated using Hardy- Weinberg equation.

Males only have one allele for this gene

Males cannot be heterozygous

The Hardy Weinberg equation assumes all individuals have two alleles for the gene

Dystrophin is a protein needed to maintain the structure of muscle cells.

In DMD the affected allele prevents the production of this protein, leading to symptoms that include a progressive effect on muscle tissue.

 Stem cells are a potential treatment for DMD.

Explain why stem cells from a healthy donor may provide a treatment for this disorder.

Stem cells can differentiate into muscle cells

These cells will not have the affected allele

Dystrophin will be produced

Name the type of inheritance shown in this example

Incomplete dominance

What is the probability of the offspring from the same parents being roan?

(Offspring in the image from the same parents)

50%

Genes A, B and C are located on two different pairs of chromosomes. What combination of alleles could only be present if crossing over has occurred?

• ABC

• aBC

• ABc

• Abc

ABc

Sperm cells have adaptations for their functions as make gametes. Describe how the acrosome is involved in the digestion of the zona pellucida.

The membrane of the acrosome fuses with the membrane of the sperm cell

Releasing enzymes

By exocytosis

The phenotype of organisms is affected by genotype.

Achondroplasia is a genetic condition that causes dwarfism in humans.

Genetic screening can be used to identify achondroplasia in embryos.

Individuals that are heterozygous for achondroplasia have shortened limbs.

Individuals homozygous for achondroplasia will not usually survive for more than one year.

Deduce if achondroplasia is caused by a dominant or recessive allele.

Dominant

An embryo created by IVF can be screen before being placed in the mother’s uterus. Name this type of genetic screening.

Pre-implantation genetic diagnosis

Explain one ethical issue relating to the use of prenatal genetic screening

Healthy foetus could be aborted

Unethical to cause the death of a foetus