B6

Question 1

1st stage: transcription

Answer 1

takes place in the nucleus
-the base sequence of a gene is copied into a complimentary template molecule
-the mRNA now passes out of the nucleus and into the cytoplasm

Question 2

2nd stage: translation

Answer 2

-the mRNA molecule attaches to a ribosome
-amino acids are now brought to the ribosomes on carrier molecules
-the ribosomes now reads the triplets of bases on the mRNA and uses this to join up the correct amino acid in the correct order

Question 3

what are template molecules

Answer 3

-mRNA
- single stranded molecules
- they are a copy of a nucleuotide

Question 4

what are the 2 types of cell division

Answer 4

meiosis: results in the formation of four genetically non identical daughter cells
-used in sexual reproduction

mitosis:
results in the formation of 2 genetically identical daughter cells

used in asexual reproduction

Question 5

what is sexual reproduction

Answer 5

process of reproduction where the nuclei of 2 gametes (sec cells) fuse to form a zygote (a process known as fertilisation) to create genetically different offspring

Question 6

what are the key features of sexual reproduction

Answer 6

-two parents
-male and female gametes fuse
- offspring are non identical
- cells divid by meiosis

Question 7

what is asexual reproduction

Answer 7

Asexual reproduction is the process of reproduction that forms genetically identical offspring from only one parent. Asexual reproduction is common in single-celled organisms and some plants.

Question 8

what are the key features of asexual reproduction

Answer 8

• no gamete fusion
• offspring are clones
• cells divide by mitosis
• only one parent

Question 9

meiosis

Answer 9

-each cell has a pair of each chromosome (diploid cell)
- during meiosis each pair of chromosomes replicate and split in 2

• there are now 2 identical cells and the diploid cell spilts again
• haploid cell is created where there are 4 genetically different gametes that each have half the number of chromosomes found in the larger cells
• during sexual reproduction the gametes fuse to make the normal amount of chromosomes (46)

-once the cells have combined they now divide asexually by mitosis
- as soon as the cell reaches a certain size it starts to differentiate (become specialised)

Question 10

advantages of sexual reproduction

Answer 10

artificial selection - Humans can speed up artificial selection through selective breeding of plants and animals.
This depends on genetic variation.
This process has many benefits, including boosting food production and breeding fast horses.

Variation in offspring- increases the chances of a population being able to survive environmental change by natural selection.
This is because some individuals are likely to be adapted to the new conditions.

means things can evolve

Question 11

what plants can reproduce sexually or asexually

Answer 11

strawberry plants
fungi
malaria parasites

Question 12

advantages of asexual reproduction

Answer 12

if an organism can reproduce either way they normally reproduce asexually if conditions are good
because:

-it’s quicker
-no mate - more efficient, less time + energy
- lots of identical offspring - if conditions are good, identical offspring is favourable

Question 13

what is a genome

Answer 13

the entire genetic material of an organism
in the genome there are lots of levels of organisation:

Question 14

whats is inside a genome

Answer 14

DNA- double helix polymer, which means it is a polymer (a large molecule made up of many different sub units) made up of two strands forming a twisted, ladder shape.

• a gene = a small section of DNA.
  Genes code for a sequence of amino acids, which combine to give a specific protein.

Chromosomes

Long strands of DNA are coiled up to form chromosomes.
Chromosomes contain many genes.
Human body cells contain 23 pairs of chromosomes, one of each pair coming from each parent.

Question 15

what is the organisation of genetic material

Answer 15

the nucleus of eukaryotic cells contain chromosomes made from DNA molecules

Each chromosome contains a large number of genes.

Each gene tells how a specific protein should be made.

Question 16

what can the understanding of genomes help us understand more of

Answer 16

Human evolutionary and migratory history
Investigating human evolutionary history, including how humans migrated in the past

Question 17

what is DNA

Answer 17

DNA is a polymer made up of two long strands of small units that repeat throughout the structure, called nucleotides. Each of these is made up of a sugar, a phosphate and a base attached to the sugar.

Question 18

DNA structure

Answer 18

The two long strands within each DNA molecule are held together by attractions between opposite bases.

Each base has one other specific base with which it pairs:

T pairs with A.
G pairs with C.

The sugar and phosphates of nucleotides form the long strands.

Question 19

nucleotides

Answer 19

A nucleotide is made up of a phosphate and a base attached to the sugar.

The sugar and phosphates of nucleotides form the long strands.

The attraction between opposite bases holds the two strands together.

each nucleotide has a different base and there are 4 different nucleotides

Question 20

what is a codon

Answer 20

Each amino acid is coded for by a specific sequence of three bases (called a codon)

Question 21

what does the order of based on the DNA tell us

Answer 21

the order for combining amino acids to create particular proteins.

Question 22

how can we change the protein made by a gene

Answer 22

by altering the sequence of bases in that gene.

Question 23

what is a mutation

Answer 23

A mutation is a permanent change in the nucleotide sequence of DNA

Occasionally, a mutation may change the structure or shape of a protein. All genetic variants arise from mutations.

Question 24

when do mutations occur

Answer 24

Mutations happen continuously and normally only slightly affect proteins or don’t affect them at all.

Question 25

what are undesirable changes caused by mutations

Answer 25

The outcome of a mutation is almost always detrimental to protein function.

For example, in enzymes, the substrate may no longer be able to bind to the active site. In structural proteins, their strength may be reduced.

Some regions of DNA do not encode protein sequences.
The term given to these sections is non-coding DNA.

Question 26

can mutations give a survival advantage

Answer 26

More rarely, a mutation may give a survival advantage, such as resistance to an antibiotic in bacteria.

These mutations can be beneficial and represent the foundation of evolution by natural selection.

Question 27

what are alleles

Answer 27

Alleles are different forms of the same gene.

Humans have pairs of every gene and in one gene, each half of the pair may have different alleles.

People’s characteristics are determined by the alleles that they have. Alleles can either be dominant or recessive:

Question 28

what is a dominant allele

Answer 28

A dominant allele is always expressed, regardless of the identity of the other allele

It only needs one copy present to be expressed (BB or Bb).

It is represented by a capital letter, e.g. B.
If B is the allele for brown eyes:
When a person has a copy of the B allele, they will have brown eyes, no matter what other allele is present.

Question 29

what is a recessive allele

Answer 29

A recessive allele is only expressed if the other allele is also recessive.

It is represented by a lowercase letter e.g. b
It needs two copies to be present to be expressed (bb).

If b is the allele for blue eyes:
A person can only have blue eyes if both of their alleles are b.

Question 30

what terms do we use when talking about the inheritance of characteristics

Answer 30

genotype and phenotype

Question 31

what are genotypes

Answer 31

Genotype refers to the combination of alleles an organism has.

If the two alleles are different, we say that the person is heterozygous (Bb).

If the two alleles are the same, we say that the person is homozygous (BB or bb).

Question 32

what is a phenotype

Answer 32

A phenotype is an observed characteristic of an individual.

The phenotype is determined by the interaction between the genotype and environment.

Earlobes being attached or free is an example of a phenotype, where the alleles present will determine a characteristic, unless the environment interferes.

Question 33

what is monohybrid inheritance

Answer 33

refers to the inheritance of traits determined by a single gene.

Question 34

what are punnet squares

Answer 34

Punnett squares are diagrams that help us to visualise the outcome of a monohybrid cross. In these diagrams, a capital letter shows a dominant allele.

The alleles of the parents are drawn along the top and side of a grid.
The pairs of alleles that the offspring could have are then filled in to the grid

Question 35

what is discontinuous variation

Answer 35

variation controlled by genes alone and is inherited

Question 36

what is continuous variation

Answer 36

characteristics you inherit but environment can influence

genes you can measure

Question 37

what are acquired characteristics

Answer 37

characteristics caused by environment

features acquired during life

not coded for in DNA

cant be passed on or inherited

Question 38

why do not identical twins look similar

Answer 38

comes form different genes inherited from parents

genes are mixed up so offspring looks similar but different from parents