Genetic Inheritance

Question 1

Alleles

definition

Answer 1

Different forms of the same gene

Question 2

Amino acid

definition

Answer 2

The building blocks that make up a protein molecule

Question 3

Chromosome

definition

Answer 3

The structure made of DNA that codes for all the characteristics of an organism

Question 4

Dominant

definition

Answer 4

An allele that always expresses itself whether it is partnered by a recessive allele or by another like itself

Question 5

Evolution

definition

Answer 5

The change of inherited characteristics within a population over time through natural selection, which may result in the formation of a new species

Question 6

what is a gene?

Answer 6

The basic unit of genetic material inherited from our parents. A gene is a small section of DNA in a chromosome. Each gene has the code for creating a specific protein. The sequence of bases in the gene controls which amino acids are joined in order to make a specific new protein (or enzyme) molecule. The proteins are then folded into their correct shape to make them functional.

Question 7

Genome

definition

Answer 7

The complete set of DNA found in an organism

Question 8

Genotype

definition

Answer 8

The alleles that an organism has for a particular characteristic, usually written as letters

Question 9

Heredity

definition

Answer 9

Genetic information that determines an organism’s characteristics, passed on from one generation to another. To do with passing genes to an offspring from its parent or parents

Question 10

Heterozygous

definition

Answer 10

This describes a genotype in which the two alleles for a particular characteristic are different

Question 11

Homozygous

definition

Answer 11

This describes a genotype in which the two alleles for the characteristic are identical

Question 12

Ionising radiation

definition

Answer 12

Radiation that is able to remove electrons from atoms or molecules to produce positively charged particles called ions

Question 13

What is lichen?

Answer 13

A type of fungus that grows on rock

Question 14

What is a Mutagen?

Answer 14

A physical or chemical agent that can induce or increase the frequency of mutation in an organism

Question 15

Mutation

definition

Answer 15

A mutation is a change in a gene or chromosome. Mutations arise spontaneously and happen continually. It can be inherited.

Question 16

What is a pedigree chart

Answer 16

A family tree diagram which show the inheritance of a genetic condition in a family, eg cystic fibrosis

Question 17

Phenotype

definition

Answer 17

The visible characteristics of an organism which occur as a result of its genes

Question 18

Radiation

definition

Answer 18

Energy carried by particles from a radioactive substance, or spreading out from a source

Question 19

Recessive

definition

Answer 19

Describes the variant of a gene for a particular characteristic which is masked or suppressed in the presence of the dominant variant. A recessive gene will remain dormant unless it is paired with another recessive gene

Question 20

Mutation and variation

Answer 20

Extensive genetic variation is contained within any species.

Variation within genes leads to different genotypes, and this can be seen by a different phenotype. Genetic variation and environmental variation can both cause these different phenotypes. All variation arises from mutations and most have no effect on the phenotype.

Question 21

If mutations cause a change in phenotype

basis of natural selection

Answer 21

A mutation rarely creates a new phenotype, but if the phenotype is changed as a result of a mutation and the new phenotype is suited to a particular environment, it can lead to a change in a species over time.

For example, if a mutation leads to a change in phenotype, such as feather colouring in birds, this change may allow those individuals to reproduce more frequently, due to them being more attractive and seen as a more desirable mate. This would result in the mutated gene being passed on more frequently than the original gene and would result in an increase in the proportion of birds with the new feather colour compared to the original feather colour. This is the basis of natural selection.

Question 22

Natural selection and survival of the fittest definition.

Answer 22

Natural selection describes how organisms that are better adapted to an environment are more likely to survive long enough to reproduce and pass on their genes. This process is called ‘survival of the fittest’ and is fundamental to the process of evolution.

Question 23

Causes of mutation

Answer 23

Mutation occurs continuously and can be spontaneous. It can also happen because of:

• ionising radiation
• chemical mutagen, such as tar from cigarette smoke
• inherited

Question 24

Radiation and mutation

Answer 24

The greater the dose of radiation a cell gets, the greater the chance of a mutation.

Question 25

types of ionising radiation

Answer 25

Ionising radiation includes gamma rays, X-rays and ultraviolet rays.

Question 26

mutation

Answer 26

Mutations could cause different genes to be switched on or off, and this could create a different or faulty protein to be synthesised. For example, if the protein is an important enzyme, the specific substrate might not fit into the substrate binding site. If it is a structural protein such as collagen, it might lose its strength.

However, most DNA mutations do not significantly alter a protein, they only alter it slightly, or not at all, so its appearance or function is not changed.

Mutations can be positive and give an organism an advantage or negative and give a disadvantage but mutations that have a significant effect are rare. Some mutations may have a small effect but most mutations have no effect on the organism. They do not change to the organism’s phenotype.

Question 27

Inversion
Deletion
Insertion
Substitution

Answer 27

These mutations may change the activity of a protein if they occur within a gene. This might result in a change in phenotype or it might appear hidden, and be unnoticed. Alternatively, they might result in a serious consequence, such as genetic disease like cystic fibrosis.

Question 28

Gregor mendel
alleles
Basis of our understanding of inheritance

Answer 28

In the mid-19th century Gregor Mendel (1822-1884) studied the inheritance of different characteristics in pea plants. He found that when he bred red-flowered plants with white-flowered plants, all the offspring produced red flowers. This went against the prediction that the colours would blend to produce pink flowers. If he bred these plants with each other, most of the offspring had red flowers, but some had white. This was because the allele for red flowers is dominant and the allele for white flowers is recessive.

Question 29

Gregor mendel

discovery of genes

Answer 29

One of Mendel’s observations was that the inheritance of each characteristic is determined by ‘units’ that are passed on to descendants unchanged. We now know these as genes.

Question 30

Mendel’s work expanded the knowledge of genetic inheritance before what had even been discovered?

Answer 30

Mendel’s work expanded the knowledge of genetic inheritance before DNA had even been discovered.

Question 31

Mendel’s work was not accepted by most scientists when he was alive for three main reasons:

Answer 31

• when he presented his work to other scientists he did not communicate it well so they did not really understand it
• it was published in a scientific journal that was not well known so not many people read it
• he could not explain the science behind why characteristics were inherited

Question 32

Discovery of chromosomes

19th century

Answer 32

The idea that genes were located on chromosomes emerged in the late 19th century when better microscopes and staining techniques allowed the visualisation and behaviour of chromosomes during cell division.

Question 33

Discovery of genes

20th century

Answer 33

In the early 20th century, it was observed that chromosomes and Mendel’s ‘units’ behaved in similar ways. This led to the theory that the ‘units’, now called genes, were located on chromosomes.

Question 34

Discovery of DNA

20th century

Answer 34

In the mid-20th century two scientists, James Watson and Francis Crick worked out the structure of DNA. By using data from other scientists Rosalind Franklin and Maurice Wilkins, they were able to build a model of DNA. They showed that bases occurred in pairs, and X-ray data showed that there were two strands coiled into a double helix. This model was used to work out how genes code for proteins.

Question 35

Genetic key terms

Answer 35

• Chromosomes are contained inside the cell’s nucleus. These are long strands of DNA, which are made up of many genes.
• A gene is a small section of DNA on a chromosome, that codes for a particular sequence of amino acids, to make a specific protein. It is the unit of heredity, and may be copied and passed on to the next generation.
• DNA is a large and complex polymer, which is made up of two strands forming a double helix. DNA determines the characteristics of a living organism. With the exception of identical twins, each person’s DNA is unique.
• DNA is made from base pairs which always come in the following combinations A-T, T-A, C-G and G-C. The order of these letters makes up an organism’s genetic code.
• An organism’s genome is one copy of all of their DNA. With the exception of identical twins, no two people’s genomes are the same.

Question 36

alleles

Answer 36

Some characteristics are controlled by a single gene, such as fur in animals and red-green colour blindness in humans. Each gene might have different forms, and these are called alleles.

Question 37

Where are chromosomes found?

Answer 37

Chromosomes are found in the nucleus of a body cell in pairs.

Question 38

where do chromosomes come from?

Answer 38

chromosomes come in pairs.
one inherited from the mother.
one inherited from the father.

Question 39

genes in chromosomes

Answer 39

The chromosome in each pair carries the same gene in the same location. These genes could be the same, or different versions.

Question 40

Dominant alleles

Answer 40

A dominant allele is always expressed, even if one copy is present. Dominant alleles are represented by a capital letter, for example you could use a B. The allele for brown eyes, B, is dominant. You only need one copy of this allele to have brown eyes. Two copies will still give you brown eyes.

Question 41

Recessive alleles

Answer 41

A recessive allele is only expressed if the individual has two copies and does not have the dominant allele of that gene. Recessive alleles are represented by a lower case letter, for example, b. The allele for blue eyes, b, is recessive. You need two copies of this allele to have blue eyes.

Question 42

Monohybrid crosses

Answer 42

Genetic crosses of single gene combinations (monohybrid inheritance) can be shown and examined using Punnett squares. These show the possible offspring combinations that could be produced, and the probability of these combinations can be calculated.

Question 43

How to construct Punnett squares

Answer 43

1) Determine the parental genotypes. You can use any letter you like but select one that has a clearly different lower case, for example: Aa, Bb, Dd.
2) Split the alleles for each parent and add them into your Punnett square around the edges.
3) Work out the new possible genetic combinations inside the Punnett square.

You may be asked to comment on the proportion of different allele combinations in the offspring, calculate a probability, ratio or just determine the phenotypes of the offspring.

Question 44

Family trees
Pedigree analysis
definition and uses

Answer 44

Doctors can use a pedigree analysis chart to show how genetic disorders are inherited in a family. They can use this to work out the probability that someone in a family will inherit a condition. A pedigree analysis is usually undertaken if families are referred to a genetic counsellor following the birth of an affected child.

Question 45

Calculations - Using probability, direct proportion and simple ratios

Answer 45

You can express the outcome of a genetic cross using probability (percentages), direct proportion or ratios. It is important to remember during the process of fertilisation, the allele combinations created are a random process, and that is why probability is used, as nothing is guaranteed. Each of the four possible offspring combinations is as likely to happen during every fertilisation event.

Question 46

What percentage of offspring have blue eyes from a cross between two heterozygous parents?

Answer 46

25%

Question 47

What percentage of offspring have blue eyes from a cross between two homozygous dominant parents?

Answer 47

50%