B1.13/14/15/16 - Variation and Inheritance

Question 1

What characteristics are determined by the environment?

Answer 1

• Scars (You may get injured and become scarred, your children will not have these same scars when they are born)
• Learning to speak a language (You have to learn to speak by copying your parents and other people, without hearing other people speak you will never master a language.)

Question 2

What characteristics are determined by genes?

Answer 2

These characteristics may be inherited:

• Eye colour
• Earlobe shape
• Nose shape

Question 3

Give two examples of a characteristic that may be both determined by genes and the environment

Answer 3

• For example, you may inherit genes that control brain development in a way that will make you able to have a very high intelligence. However, if you are not fed properly whilst growing up, or if no-one talks to reads to you, or you are not given lessons you will not develop your full intelligence.
• You may have the genetic potential to be very tall, but will not be if you are undernourished.

Question 4

What are chromosomes?

Answer 4

Chromosomes are the thread like structure inside the nucleus of each cell which carries genetic information in the form of genes.

Question 5

What is a gene?

Answer 5

Genes are particular regions of a chromosome.

Question 6

What are chromosomes made up of?

Answer 6

Chromosomes are made of a chemical called DNA. Each gene is a length of DNA. Each gene controls the development of a particular characteristic.

Question 7

How many chromosomes does every nucleus of every cell in your body contain (expect red blood cells as they do not have a nucleus)?

Answer 7

Each cell contains 23 matching pairs of chromosomes. 46 altogether.

Question 8

How many chromosomes do gametes, eggs and sperms have?

Answer 8

They have half the number in body cells. So 23 chromosomes (not 23 pairs, 23 single chromosomes)

Question 9

What is the Nature -Nurture debate?

Answer 9

The Nature-Nurture debate is the argument whether nature (genes) or nurture (environment) effects the outcome of certain characteristics more than the other. Recently scientists believe that it is a mixture of both that determine the outcomes of certain characteristics.

Question 10

What is genetic variation?

Answer 10

Genetic variation refers to diversity in genetic characteristics. Genetic variation can refer to differences between individuals or to differences between populations.

Question 11

What causes genetic variation?

Answer 11

Mutations, formation of gametes, and fertilisation can all produce variation.

Question 12

Sometimes mutations change the structure of a gene. Some mutations just happen spontaneously (no external cause). A mistake happens when DNA is being copied before cells divide. What factor in the environment, may cause mutations?

Answer 12

• Chemicals (tar) in tobacco smoke
• Chemicals used for dying materials
• Ultraviolet radiation in sunlight
• Ionising radiation like X-rays and gamma rays.

Question 13

What is a mutation?

Answer 13

The changing of the structure of a gene, resulting in a variant form which may be transmitted to subsequent generations, caused by the alteration of genes in DNA, or the deletion, insertion, or rearrangement of larger sections of genes or chromosomes.

Question 14

What is an allele?

Answer 14

A mutation may change a gene to a different version, called an ALLELE. It still codes for the same characteristic but will produce a slightly different version of the characteristic. E.g the gene for earlobes has two alleles, one codes for free lobes, the other codes for attached lobes.

Question 15

What are gametes?

Answer 15

Gametes are special sex cells. They only contain 23 chromosomes, instead of 46.

Question 16

What are the female gametes and what are the male gametes?

Answer 16

• Female: Eggs

- Male: Sperm

Question 17

Why do gametes only have 23 chromosomes, instead of 46?

Answer 17

Gametes are made from body cells by a special type of cell division. The body cell has 23 pairs of chromosomes. The pairs separate during cell division.

Question 18

Why does gamete formation produce genetic variation?

Answer 18

• During the cell division, the chromosomes in each pair may swap pieces with each other, giving them different combinations of alleles, but still retaining the same genes.
• The way the two copies (chromatids) separate from each other during the second division is random.

This means that every egg a woman produces and every sperm a man produces is genetically different. Each gamete is genetically unique.

Question 19

How does fertilisation cause genetic variation?

Answer 19

Fertilisation is random and produces genetic variation. This is because each egg and each sperm produced by the mother/father is genetically different. The father makes many sperms and any one of them can join with the egg. As a result every individual will be genetically unique.

Question 20

In a fertilised egg, how many chromosomes come from the mother and how many come from the father?

Answer 20

23 chromosomes come from the father and 23 come from the mother. 50/50. The mixture of genetic information from the two parents leads to genetic variation in the individual.

Question 21

Why does the radiographer go out of the room while the patient is being scanned?

Answer 21

This is so that the radiographer is not exposed to X-rays while carrying out their work.

Question 22

What is a dominant characteristic/allele?

Answer 22

A dominant allele always shows, even if the individual only has one copy of the allele. For example, the allele for brown eyes is dominant. You only need one copy of the allele to have brown eyes (and two copies will still give you brown eyes).

Question 23

What is a recessive characteristic/allele?

Answer 23

A recessive allele only shows if the individual has two copies of the recessive allele. For example, the allele for blue eyes is recessive. You need two copies of the allele to have blue eyes.

Question 24

The offspring of mice all have an allele for brown coat and an allele for white coat, but the brown coat is expressed (seen). We can say the allele for the brown coat is dominant and the allele for the white coat is recessive. no question

Answer 24

………..

Question 25

What makes us male or female?

Answer 25

We have 23 pairs of chromosomes in the nucleus of our body cells. One of these pairs of chromosomes determines sex (gender). If in that pair you have two large X chromosomes, you are female. If you have one large X chromosome and a smaller Y chromosome you are male.

Question 26

At pregnancy what is the chance of conceiving a boy or girl?

Answer 26

There is a a 50:50 chance. You can see this in a larger population, there will be equal numbers of males and females.

Question 27

What is your phenotype?

Answer 27

The physical appearance of the gene you carry for a particular characteristic (e.g earlobe shape).

Question 28

What is genotype?

Answer 28

The genetic composition of an individual organism.

Question 29

How can one be heterozygous?

Answer 29

One is heterozygous if they have two different versions of a gene for the same characteristic.
E.g you may receive the gene coding for a free earlobe from your father, but the gene coding for an attached earlobe from your mother. The gene/allele for a free earlobe will be expressed since it is dominant. This individual is heterozygous

Question 30

How can one be homozygous?

Answer 30

One is homozygous only if they have two versions of the same gene coding for a particular characteristic.
E.g If you receive a gene coding for attached earlobes from your mother and father, an attached earlobe will be expressed since it is recessive. This individual is homozygous.

Question 31

What is a monohybrid cross?

Answer 31

A monohybrid cross is a mating between individuals who have different alleles for one particular genetic characteristic.

Question 32

How is a dominant allele presented differently to a recessive allele in a genetic diagram?

Answer 32

A dominant allele is written with a capital letter whereas a recessive allele is written in lower case.

Question 33

If a mother passes on an allele for attached earlobes to their offspring and the father passes on an allele for free earlobes, what characteristic will be expressed in the offspring? Why? When would the other be expressed?

Answer 33

The free earlobe will be expressed as it is the dominant allele. The attached earlobe allele will only be expressed if two attached earlobe alleles are passed onto the offspring.

Question 34

What causes inherited disorders?

Answer 34

Faulty genes causes inherited disorders.

Question 35

Name three inherited disorders

Answer 35

• Cystic Fibrosis
• Red-green colour blindness
• Sickle cell anaemia

Question 36

Most (but not all) of the faulty alleles that cause genetic disorders are recessive, so a person only has the disorder if they inherit two faulty alleles. It may be that neither parent had the disease, but both had a faulty allele and were carriers.

Answer 36

…………………..

Question 37

Give two examples of useful mutations

Answer 37

• Humans who lived in Africa had dark skin which prevented sun burn from the intense sunlight. However, paler skin is more useful in areas with less sunlight as it allows the sun’s less intense rays to penetrate the skin and produce vitamin D.
• The mutation of the gene FOXP2 allowed humans to develop speech and enable them to talk.