Sex determination

Sperm cells are involved in fertilisation.

The diagram shows a human sperm cell.

Label the nucleus of this sperm cell.

State the number of chromosomes in the nucleus of this sperm cell.

State what is meant by the term fertilisation.

Dairy farmers want their cows to produce more female offspring. Scientists have developed a method to increase the percentage of female offspring from cows.

Suggest why dairy farmers want their cows to produce more female offspring.

In the scientists’ method, sperm cells containing X chromosomes are separated from sperm cells containing Y chromosomes. This is their method.

• add sperm cells to a solution of dye that stains DNA, so that the DNA reflects light

• pass the sperm cells through a cell sorter

• shine light on the sperm cells as they pass through the sorter

• separate the sperm cells into different tubes depending on the amount of light they reflect

Suggest how the scientists’ method can separate sperm cells containing an X chromosome from those containing a Y chromosome.

Scientists carried out an investigation to find out how successful a cell sorter is in separating X and Y chromosomes.

Sperm cells from the cell sorter produced 43 females out of a total of 44 offspring. Calculate the success of producing females as a percentage of the total number of offspring.

Give the control experiment that should be used in this investigation.

Predict the results of the control experiment.

The passage describes reproduction in humans and in chickens. Complete the passage by writing a suitable answer in each blank space.

In humans, the hormone called_........ stimulates the repair of the

uterus lining. The ovum is then released from the_........ .

The ovum has a haploid number of 23 chromosomes.

Fertilisation occurs in the_........ tube. Fertilisation results

in a single cell called a_........ with a diploid number

of_........ chromosomes. This cell divides

by_........ to produce an embryo.

Sex inheritance in chickens is different from humans. In chickens the sex chromosomes are

called Z and W. In humans, the sex chromosomes are called_........ .

The sex chromosomes of a male chicken are ZZ and of a female chicken are ZW. This means that

the probability of parent chickens producing a male offspring is_........ .

In pigeons, the inheritance of bars at the end of the wings is controlled by a gene with two alleles. The allele for wing bars (B) is dominant to the allele for no wing bars (b). The diagram shows the phenotype of a pigeon with wing bars and the phenotype of a pigeon with no wing bars.

In a first cross, a heterozygous parent mates with a homozygous recessive parent. Complete the table by giving the genotype of each parent and the possible phenotypes of their offspring.

In a second cross, two heterozygous pigeons mate. Give the possible genotypes of their offspring.

This second cross only produces one offspring. Give the probability that this offspring will have wing bars.

Galactosaemia is an inherited condition. It is caused by a mutation to a gene on chromosome 9. This gene codes for an enzyme that removes the sugar galactose from the body. The normal allele, G, can produce the enzyme and is dominant to the recessive allele, g. The pedigree shows the inheritance of galactosaemia in a family.

How many individuals in the family pedigree have an X and a Y chromosome in each of their body cells?

How many individuals in the family pedigree are homozygous recessive?

Give the genotype of individual 1.

Individuals 8 and 9 are going to have another child. Give the probability of this child having galactosaemia.

What is meant by the term mutation ?

The mutation for galactosaemia is harmful but some mutations can be beneficial. Describe one example of a beneficial mutation.

Some inherited conditions can be fatal but medical treatment is often available. Explain what would happen to the frequency of alleles for these inherited conditions if medical treatment was not available.

4 (a) A student reads the following statement. “the father determines the sex of a baby” Explain why this statement is true.

The diagram shows sperm cells, viewed using a microscope, from two different men.

Use the information in the diagram to give two reasons why man A is more fertile than man B.

The graph shows how smoking may affect the movement of sperm.

The average (mean) sperm count in the semen from non-smokers is 55 million in 1 cm³. Calculate the number of moving sperm in 1 cm³ of semen from the non-smokers.

number of moving sperm =_........

Use the information from the graph to explain why smoking could affect male fertility.

In mammals, males have two different sex chromosomes (X and Y) and females have two similar sex chromosomes (X and X). However, in birds males have two similar sex chromosomes (Z and Z), while females have two different sex chromosomes (Z and W).

Complete the genetic diagram to show how sex is inherited in birds.

Genotype of male parent Genotype of female parent

Gametes from male parent Gametes from female parent

Genotypes of offspring

Sex of offspring

In birds, the egg is extremely large and contains food molecules that the growing embryo needs in order to develop.

Suggest one food molecule that is present in a bird’s egg and describe the role of this molecule in the growth of the bird embryo.

Suggest an advantage of the shell of the egg being made of a hard substance.

Chicken eggs are a rich source of vitamin A. Give another source of vitamin A and describe the function of vitamin A in humans.

The number of chromosomes in eggs and in sperm is less than the number of chromosomes in the body cells of animals. Explain how the number of chromosomes in animals is maintained in their offspring.