Sex determination

Some people keep rabbits as pets.

Figure 1 shows two types of rabbit.

The fur colour pattern in the Himalayan rabbit is caused by a dominant allele.

What is a dominant allele?

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In Questions 01.2 and 01.3, use the following symbols: H = dominant allele for Himalayan fur pattern h = recessive allele for white fur.

What is the genotype of a white rabbit?

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A male Himalayan rabbit was crossed with a female Himalayan rabbit.

The male rabbit and the female rabbit each had the heterozygous genotype Hh.

Some of the offspring were Himalayan rabbits and some of the offspring were white rabbits.

Complete the Punnett square diagram in Figure 2.

You should show:

• the male gametes

• the offspring genotypes.

Some of the offspring in Figure 2 are homozygous and some are heterozygous.

Draw a ring around the genotype of one homozygous offspring in Figure 2.

Four offspring were born.

How many of the four offspring would you expect to be Himalayan rabbits?

Use Figure 2.

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Inheritance of sex in rabbits is the same as inheritance of sex in humans.

A female rabbit has two X chromosomes in each body cell.

How many X chromosomes does a male rabbit have in each body cell?

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Some of the offspring in Figure 2 would be male and some of the offspring would be female.

How many of the four offspring in Question 01.5 would you predict to be female?

Reproduction can produce offspring which are:

• genetically different or

• genetically identical.

Farmers grow tomato plants in greenhouses.

The tomatoes are sold in supermarkets.

Suggest one advantage of growing tomato plants that are genetically different.

Suggest one advantage of growing tomato plants that are genetically identical.

Scientists can grow genetically identical tomato plants using tissue culture.

What is tissue culture?

Genetically identical tomato plants growing in the same garden do not all grow to the same height.

Give one reason why.

The sex of dogs is determined by X and Y chromosomes in the same way as in humans.

Complete the Punnett square diagram in Figure 15 to show the inheritance of sex in dogs.

Use the symbols X and Y.

Figure 15

A female dog gave birth to six offspring.

Why would you expect there to be three male offspring and three female offspring?

Use your answer to Question 09.5.

Farmers keep chickens for:

• meat production

• egg production.

Some varieties of chicken grow more quickly and are more suitable for meat production.

Other varieties of chicken produce more eggs.

A farmer keeps two varieties of chicken, A and B.

The farmer investigated the growth rates and egg-production rates of both varieties.

Figure 16 shows the results.

Suggest two control variables the farmer should have used in this investigation.

Figure 16 shows mean values from 500 chickens of each variety.

Give the reason the farmer used a large number of chickens.

The farmer wants to produce a new variety of chicken that is good for both meat production and egg production.

Describe how selective breeding of chicken varieties A and B can produce the new variety of chicken.

Reproduction can produce offspring which are:

• genetically different or

• genetically identical.

Farmers grow tomato plants in greenhouses. The tomatoes are sold in supermarkets.

Suggest one advantage of growing tomato plants that are genetically different.

Suggest one advantage of growing tomato plants that are genetically identical.

Scientists can grow genetically identical tomato plants using tissue culture. What is tissue culture?

Genetically identical tomato plants growing in the same garden do not all grow to the same height. Give one reason why.

The sex of dogs is determined by X and Y chromosomes in the same way as in humans.

Complete the Punnett square diagram in Figure 4 to show the inheritance of sex in dogs. Use the symbols X and Y.

Figure 4

A female dog gave birth to six offspring. Why would you expect there to be three male offspring and three female offspring? Use your answer to Question 03.5.

Farmers keep chickens for:

• meat production

• egg production.

Some varieties of chicken grow more quickly and are more suitable for meat production. Other varieties of chicken produce more eggs. A farmer keeps two varieties of chicken, A and B. The farmer investigated the growth rates and egg-production rates of both varieties. Figure 5 shows the results.

Suggest two control variables the farmer should have used in this investigation.

Figure 5 shows mean values from 500 chickens of each variety. Give the reason the farmer used a large number of chickens.

The farmer wants to produce a new variety of chicken that is good for both meat production and egg production. Describe how selective breeding of chicken varieties A and B can produce the new variety of chicken.

Sperm cells and egg cells are formed by meiosis.

During meiosis a cell divides twice.

How many sperm cells are formed when a cell divides by meiosis?

Human body cells contain 46 chromosomes.

How many chromosomes are in each human egg cell?

Dupuytren’s is a disorder that affects the hands.

One form of Dupuytren’s is caused by a dominant allele (D).

The allele for not having Dupuytren’s is recessive (d).

What is an allele?

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A man with Dupuytren’s has the genotype Dd.

Which word describes the man’s genotype?

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The man with Dupuytren’s (Dd) and a woman who does not have Dupuytren’s (dd) plan to have a child.

Complete the genetic diagram in Figure 4 to show the possible genotypes of the child.

Draw a ring around the genotype of a child in Figure 4 who will have Dupuytren’s.

What is the chance of the child having Dupuytren’s?

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A genetic disorder develops as a result of a change in a gene.

What scientific term describes a change in a gene?

People with a family history of some genetic disorders are offered embryo screening.

Suggest one way embryo screening can help people with a family history of a genetic disorder.

There are two types of cell division: mitosis and meiosis.

Describe three differences between the processes of mitosis and meiosis.

Describe one similarity between the processes of mitosis and meiosis.

Dupuytren’s is a disorder that affects the hands.

Figure 6 shows the inheritance of Dupuytren’s in one family.

Dupuytren’s is caused by a dominant allele in this family. D = dominant allele d = recessive allele

Give the genotype of person 1. Explain your answer.

Person 7 and person 8 in Figure 6 are expecting a fourth child. What is the probability of the child having Dupuytren’s? You should:

• draw a Punnett square diagram

• identify which offspring have Dupuytren’s

Explain how Figure 6 shows the allele for Dupuytren’s is not on the Y chromosome.

The shape of a person’s earlobes is controlled by a gene.

Figure 3 shows two types of earlobe.

A dominant allele codes for free earlobes.

What is a dominant allele?

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A man with free earlobes and a woman with attached earlobes have children together.

Complete Figure 4 to show the possible genotypes of the children.

Use the symbols:

E = allele for free earlobes e = allele for attached earlobes

What is the probability that one of the children would have attached earlobes?

Use Figure 4.

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Figure 5 shows the inheritance of the sex chromosomes, X and Y.

Complete Figure 5 to show the sex chromosomes in the gametes of the man and the woman.

Calculate the probability that the man and the woman’s next child will be a girl with attached earlobes.

Use the equation:

probability of a girl with attached earlobes

= probability of attached earlobes probability of being a girl

Figure 6 shows the production of sperm cells in humans.

Cell A is a normal body cell.

How many chromosomes are there in cell A ?

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What is the mass of DNA in cell E ?

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What type of cell division produces sperm cells?

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Sometimes there are errors in copying the genetic material.

What term describes an error in the genetic material?

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A woman has three children, aged 4, 6 and 9 years.

Why are the children not genetically identical?

In sexual reproduction, a sperm cell fuses with an egg cell to form a new single cell.

An embryo develops from the single cell.

The cell divides three times to produce the embryo.

How many cells are there in the embryo after three cell divisions?

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Figure 7 shows a different human embryo.

Measure image length X on Figure 7.

Give your answer in millimetres (mm).

The image in Figure 7 has been magnified 500

Calculate the real length of the embryo.

Use the equation:

Give your answer in micrometres (m).

The embryo may not implant in the lining of the uterus.

The embryo will then be lost from the woman’s body several days later.

Explain why the woman may not notice this has happened.