Inheritance and variation-mocks

Question 1

Why are some disorders inherited?

Answer 1

-They can be caused by the inheritance of certain alleles

Question 2

Examples of inherited genetic disorders:

Answer 2

• PolyDactyly (dominant allele)
• Cystic fibrosis
• huNtington’s disease (domiNant allele)
• down syndrome
• sickle cell anemia

Question 3

Cystic fibrosis

Answer 3

-Cystic fibrosis is a genetic disorder of cell membranes
-It results in the body producing large amounts of thick, sticky mucus in the air passages
-Over time, this may damage the lungs and stop them from working properly
-Cystic fibrosis is caused by a recessive allele (f)
This means:
-People who are heterozygous (only carry one copy of the recessive allele) won’t be affected by the disorder but are ‘carriers’
-People must be homozygous recessive (carry two copies of the recessive allele) in order to have the disorder
-If both parents are carriers, the chance of them producing a child with cystic fibrosis is 1 in 4, or 25%
-If only one of the parents is a carrier (with the other parent being homozygous dominant), there is no chance of producing a child with cystic fibrosis

Question 4

Polydactly

Answer 4

-Polydactyly is a genetic disorder that causes someone to be born with extra fingers or toes
-Polydactyly is caused by a dominant allele (D)
This means:
-Even if only one parent is a carrier, the disorder can be inherited by offspring

Question 5

nucleotides have exactly the same

Answer 5

phosphate sugar backbone

Question 6

4 nucleotides

Answer 6

adenine
cytosine
guanine
thymine

Question 7

Protein synthesis

Answer 7

1, The DNA molecule unzips/unwinds by the enzyme RNA polymerase breaking the hydrogen bonds into the single strand.
2, Transcription is when the gene is copied onto the RNA strand.
3, mRNA leves the nucleus, enters the cytoplasm and attatches itself to the ribosome.
4, The ribosomes will ‘read’ the codon for a specific amino acid which is translation. Amino acid chains will join to form a polypeptide, which is created by tRNA.
5, Polypeptide will form the appropriate protein (growth and repair).

Question 8

gene

Answer 8

a section of DNA that codes for a specific sequence of amino acids

Question 9

allele

Answer 9

a version/form of a particular gene or a mutation

Question 10

genotype

Answer 10

the inherited alleles that will determine the phenotype

Question 11

phenotype

Answer 11

the physical expression of the genotype

Question 12

homozygous

Answer 12

a pair of identical alleles

Question 13

dOmiNant

Answer 13

only one allele needs to be present for the phenotype/genetic disorder to be expressed

Question 14

Gametes

Answer 14

They are sex cells (in animals:sperm and ovum, in plants:pollen nucleus and ovum).

Question 15

Chromosomes

Answer 15

• thread-like structures of DNA, carrying genetic information in the form of genes. They are located in the nucleus of cells

Question 16

recessive

Answer 16

both alleles need to be present for the phenotype/genetic disorder to be expressed

Question 17

homozygous

Answer 17

a pair of identical alleles

Question 18

heterozygous

Answer 18

a pair of non-identical alleles

Question 19

Monohybrid inheritance

Answer 19

Some characteristics are controlled by a single gene, such as fur colour in mice; and red-green colour blindness in humans
The inheritance of these single genes is called monohybrid inheritance (mono = one)
As we have two copies of each chromosome, we have two copies of each gene and therefore two alleles for each gene
One of the alleles is inherited from the mother and the other from the father
This means that the alleles do not have to ‘say’ the same thing
For example, an individual has two copies of the gene for eye colour but one allele could code for brown eyes and one allele could code for blue eyes
The observable characteristics of an organism (seen just by looking – like eye colour; or found – like blood type) is called the phenotype
The combination of alleles that control each characteristic is called the genotype
Alleles can be dominant or recessive
A dominant allele only needs to be inherited from one parent in order for the characteristic to show up in the phenotype
A recessive allele needs to be inherited from both parents in order for the characteristic to show up in the phenotype.
If there is only one recessive allele, it will remain hidden and the dominant characteristic will show
If the two alleles of a gene are the same, we describe the individual as being homozygous (homo = same)
An individual could be homozygous dominant (having two copies of the dominant allele), or homozygous recessive (having two copies of the recessive allele)
If the two alleles of a gene are different, we describe the individual as being heterozygous (hetero = different)
When completing genetic diagrams, alleles are abbreviated to single letters
The dominant allele is given a capital letter and the recessive allele is given the same letter, but lower case

Question 20

Polygenic inheritance

Answer 20

Most characteristics are a result of multiple genes interacting, rather than a single gene
Characteristics that are controlled by more than one gene are described as being polygenic
Polygenic characteristics have phenotypes that can show a wide range of combinations in features
The inheritance of these polygenic characteristics is called polygenic inheritance (poly = many/more than one)
Polygenic inheritance is difficult to show using genetic diagrams because of the wide range of combinations
An example of polygenic inheritance is eye colour – while it is true that brown eyes are dominant to blue eyes, it is not as simple as this as eye colour is controlled by several genes
This means that there are several different phenotypes beyond brown and blue; green and hazel being two examples
-many characteristics are controlled by a group of genes and this is known as polygenic inheritance

Question 21

Punnett square diagram

Answer 21

• A Punnett square diagram shows the possible combinations of alleles that could be produced in the offspring
• From this, the ratio of these combinations can be worked out
• However, you can also make predictions of the offsprings’ characteristics by calculating the probabilities of the different phenotypes that could occur

Question 22

genome

Answer 22

The entire set of the genetic material of an organism

Question 23

Differences between RNA and DNA

Answer 23

• Instead of having the bases thymine, RNA is replaced by uracil
• RNA is only one strand

Question 24

DNA

Answer 24

• It is genetic material in the nucleus of a cell
• It is a polymer made up of two strands forming a double helix
• it is found in chromosomes

Question 25

Gene

Answer 25

It is a small section of a chromosome. Each gene codes for a specific sequence of amino acids. (these sequences of amino acids form different types of protein)

Question 26

Genome

Answer 26

Entire genetic material in an Organism

Question 27

codon

Answer 27

base triplets

Question 28

Proteins

Answer 28

- structural proteins such as collagen found in skin cells - enzymes - hormones

Question 29

genes control our

Answer 29

characteristics

Question 30

Human Genome Project

Answer 30

- The Human Genome Project (completed in 2003) was the name of the international, collaborative research effort to determine the DNA sequence of the entire human genome and record every gene in human beings - This was a very important breakthrough for several reasons: - From a medical perspective, as it has already and will continue to improve our understanding of the genes linked with different types of disease and inherited genetic disorders, as well as the help us in finding treatments - The human genome has also made it possible to study human migration patterns from the past, as different populations of humans living in different parts of the world have developed very small differences in their genomes!

Question 31

Nucleotides

Answer 31

-They consist of a common sugar and phosphate group with one of four different bases attatched to the sugar -These four nucleotides contain the same phosphate and deoxyribose sugar, but differ from each other in the base attached There are four different bases: Adenine (A), Cytosine (C), Thymine (T) and Guanine (G)

Question 32

What is the code for a particular amino acid?

Answer 32

- A sequence of three bases - The order of bases controls the order and different types of amino acids that are joined together - In this way, it is the order of bases in the DNA which eventually determines which proteins are produced

Question 33

The phosphate and sugar section of the nucleotides form the

Answer 33

backbone of the DNA strand

Question 34

Changes to proteins

Answer 34

- A change in DNA structure may result in a change in the protein synthesised by a gene - If there is a change in the order of the bases in a section of DNA (eg. in a gene), then a different protein may be produced - This protein may not function in the same way as the original protein would have (before the change occurred in the DNA)

Question 35

Protein structure

Answer 35

- When the protein chain is complete it folds up to form a unique shape - This unique shape enables the proteins to fulfil a specific function. For example, proteins can be: - Enzymes – proteins that act as biological catalysts to speed up chemical reactions occurring in the body (eg. maltase is an enzyme that breaks down maltose into glucose) - Hormones – proteins that carry messages around the body (eg. testosterone is a hormone that plays an important role in the development of the male reproductive system and development of male secondary sexual characteristics, such as increased muscle mass and growth of body hair) - Structural proteins – proteins that provide structure and are physically strong (eg. collagen is a structural protein that strengthens connective tissues such as ligaments and cartilage)

Question 36

Mutation

Answer 36

- Mutations are random changes that occur in the sequence of DNA bases in a gene or a chromosome - Mutations occur continuously - As the DNA base sequence determines the sequence of amino acids that make up a protein, mutations in a gene can sometimes lead to a change in the protein that the gene codes for - Most mutations do not alter the protein or only alter it slightly so that its appearance or function is not changed - There are different ways that a mutation in the DNA base sequence can occur.

Question 37

Insertion

Answer 37

- A new base is randomly inserted into the DNA sequence - An insertion mutation changes the amino acid that would have been coded for by the group of three bases in which the mutation occurs - Remember – every group of three bases in a DNA sequence codes for an amino acid - An insertion mutation also has a knock-on effect by changing the groups of three bases further on in the DNA sequence

Question 38

Deletion

Answer 38

-A base is randomly deleted from the DNA sequence Like an insertion mutation, a deletion mutation changes the amino acid that would have been coded for by the group of three bases in which the mutation occurs -Like an insertion mutation, a deletion mutation also has a knock-on effect by changing the groups of three bases further on in the DNA sequence

Question 39

Substitutions

Answer 39

- A base in the DNA sequence is randomly swapped for a different base - Unlike an insertion or deletion mutation, a substitution mutation will only change the amino acid for the group of three bases in which the mutation occurs; it will not have a knock-on effect

Question 40

Effects of mutations

Answer 40

- Most mutations do not alter the protein or only alter it slightly so that its appearance or function is not changed - However, a small number of mutations code for a significantly altered protein with a different shape - This may affect the ability of the protein to perform its function. For example: - If the shape of the active site on an enzyme changes, the substrate may no longer be able to bind to the active site - A structural protein (like collagen) may lose its strength if its shape changes

Question 41

Gene switching

Answer 41

- Not all parts of DNA code for proteins - Some non-coding parts of DNA can switch genes on and off - This means they can control whether or not a gene is expressed - Variations in these areas of DNA may affect how genes are expressed - If a mutation occurs in a section of non-coding DNA that controls gene expression, the expression of these genes may be altered or in some cases, the mutation may cause them not to be expressed at all

Question 42

Mutations

Answer 42

- exposure to carcinogens (harmful chemicals) and some types of radiation (increase risk of a mutation occurring) - spontaneous

Question 43

Most mutations

Answer 43

- do not have a significant effect as they will only affect the protein very slightly - most mutations occur in non-coding DNA (does not code a protein) - most non-coding DNA does not do anything but some determine whether the genes are turned on or off (off-won't be expressed)

Question 44

subsitution

Answer 44

one of the bases is substituted for another random base. Changes the codon so could change amino acid that it codes for.

Question 45

Insertion mutation

Answer 45

-extra base is inserted. A lot worse than subsitution mutation- knock-on effect. Amino acid chain after point will be completely different.

Question 46

Deletion mutation

Answer 46

-one of the bases is deleted from the sequence. Knock-on effect. Worse than subsitution mutations.