B13 Reproduction

Question 1

Difference between what is formed during miosis and mitosis

Answer 1

Meiosis leads to non-identical cells being formed and mitosis leads to identical cells being formed

Question 2

What is sexual reproduction,
What causes variety
give examples…

Answer 2

Sexual reproduction involves the fusing of male and female gametes. Gammetes are formed by miosis.
In sexual reproduction there is mixing of genetic information which leads to variety in the offspring.
Sperm and eggs in animals
Pollen and eggs cells in flowering plants

Question 3

What is asexual reproduction?

Answer 3

Involves the only one parents and no fusion of gametes. This leads to gentically identical off spring (clones). Only mitosis is involved.
Some plants and aniamls reproduce this way.

Question 4

What does miosis do (simplfied) ?

Answer 4

Miosis halves the number of chromosomes in gametes compared to normal cells through cell devision .

Question 5

Miosis:

Answer 5

• Gentic material replicated, then the chromosomes arrange themselves into pairs
• in the first devision the chrmomsome pairs line up in the centre of the cell
• the pairs are then pulled apart so each new cell has one copy of each chromosomes
• in the second devision the chromosomes line up again and the arms are pulled apart
• you get 4 gametes each with a single set of chrmosomes. Because the chromosomes are mixed (so some of the organisms father and some of the organisms mothers chromosomes are used) and they only get half of them during miosis they are gentically different from each other.

Question 6

What is fertilisation

Answer 6

Fertilisation occours when two gametes fuse together to restore the normal number of chromosomes. The new cell divides by mitosis. The number of cells increase as the embryo. As the embryo develops the cells differentiate into specialised cells.

Question 7

What is the genome of an organism

Answer 7

The entire gentic material of that organism.

Question 8

What are the postives of discovering the entire human Genome?

Answer 8

• it allows scientists to indentify genes linked to different types of disease
• knowing which genes are linked to an inherited disorders helps us better understand and treat them
• scientists could use the genome in tracing human migration patterns from the past. This is done by investigating differences in the genomes to work out when a population split off.

Question 9

What is a gene and what does it do?

Answer 9

A gene is a small section of DNA found on a chromosome. Each gene codes for (tells the cell what to make) a particular sequence of amino acids to make a specific protien.
Read CGP page.
Gene -> sequence of bases -> amino acid -> protien -> type of cell

Question 10

What is DNA and what does it compose?

Answer 10

DNA is a polymer made up of two strands forming a double helix. DNA is a chemical composes all the gentic material in the nucleus of a cell (coded information) and DNA is contained in structures called chromosomes.

Question 11

What are DNA strands made up of?

Answer 11

DNA as a polymer made from repeating nucleotides units (there are 4 different nucleotides). Each nucleotide consists of a common sugar and phosphate group with one of four different bases attached to the sugar.
The long strands of DNA consist of alternating sugar and phosphate sections (which make up the backbone to the DNA strand). Attached to each sugar is one of 4 bases A C G or T. (Each base links to an opposite strand on the helix AT or CG (complemtary base pairing))

Question 12

How is an amino acid coded for? Consequently how is a protien coded for?

Answer 12

Each gene codes for a particular sequence of amino acids to make a specfic protien
A sequences of three bases is the code for a particular amino acid. The order of bases in a gene controls the order in which amino acids are assembled to produce a particular protein.

Question 13

What is complementary base pairing

Answer 13

In the complementary strands a C is always linked to a G on the opposite strand and a T to an A. This is called complemtntary base pairing.

Question 14

Does all DNA code for protiens?

Answer 14

No, some of these non-coding parts switch genes on and off, so they control wether a gene is expressed (used to make a protien)

Question 15

Explain how protien synthesis occours in the ribosomes

Answer 15

Proteiens are made in the cytoplasm of a cell on tiny structure called ribosomes
To make protiens ribosomes use the code in DNA. However DNA is found in the nucleus and cannot move due to its size. So the Cell gets code from the nucleus to the ribosomes using a mRNA molecule.
It is made by the code being coppied (a mocule mRNA) - it then carries it to the ribosomes.
From here protiens are synthesised on ribosomes according to the order of bases in the mRNA molecule. Carrier molcules bring specfic amino acids to add to the growing protien chain in the correct order
When the protien chain is complete it folds to form a unique shape. This unique shape enables protiens to do thier job as enzymes hormones or forming structure in the body such as collagen, enzymes or hormones.

Question 16

Name some protiens

Answer 16

Ennzymes - (biological catalysts to spped the rstes of reactions in the body)

Hormones - used to carry messages around the body. Eg insulin is a hormone released into the blood by tge pancrease the regulate tye blood sugar level

Structural protiens - are physically strong, eg collagen is a structural protien that strengthens connective tissues (like ligaments and cartilage)

Question 17

What are the advantages of screen ing embryos

Answer 17

• Ethically - It will help stop people suffering (parent and children)
• Economically - Treating disorders costs the government (and tax payers) lots of money
• Socially - There are laws to prevent it going to far. At the monemnt parents cannot even select the gender of the baby (unless for health reasons)

Question 18

Gamete
Genotype 
Phentype 
Alleles
Dominant 
Ressesive 
Homozygous 
Heterozygous 
Gametes 
Offspring

Answer 18

Gamete - The sex cells (only contain one set of chromosomes so they have the amount of a normal cell when fused

Genotype - The genetic makeup of an individual regarding a particular characteristic.

Phentype - The physical appearance of an individual regarding a particular characteristic.

Alleles - Alternative forms of a gene.

Dominant - Alleles which will always be expressed in the phenotype when it is present.

Ressesive - Alleles that will only be expressed in the phenotype in the absence of a dominant allele

Homozygous - Both alleles are the same for a particular triat

Heterozygous - The alleles are different

Offspring - The generation resulting from reproduction.

Question 19

How do the aelles present or genotype operate?

Answer 19

The alleles present, or genotype, operate at a molecular level to develop characteristics that can be expressed as a phenotype.

Question 20

What are most characteristics the result of?

Answer 20

Most characteristics are a result of multiple genes interacting, rather than a single gene.
Some characteristics are controlled by a single gene, such as: fur colour (could come up in a question about pundit squars)

Question 21

Practise

Answer 21

Some characteristics are controlled by a single gene, such as: fur colou

Question 22

What is polydactyly and what alle causes it?

Answer 22

Polydactyly (having extra fingers or toes) is caused by a dominant allele

It isn’t life threatneing

Question 23

What is cystic fribrosis and wich alle causes it?

Answer 23

Cystic fibrosis (a disorder of cell membranes) is caused by a recessive allele.

Mucus bulds up in the air passages and pancrease

Question 24

What are the disadvantages ?

Answer 24

Ecnomically - screening is expensive

Ethicslly - it implies that people with gebtic disorders undesirable - which could lead to prejudice

Scocislly - there may become a point were everyone wants to screen embroyos so they can picj the most desirable one eg blue eyes

Question 25

When do mutations occour

Answer 25

Mutations occour continuously

Question 26

What is a mutation

Give examples of what mutations cause

Answer 26

A random change to an organisms DnA. It changes the sequence of bases in a gene which produces a gentic variant. Because the sequences of bases codes for a sequence of amino acids that make up a protien; A few mutations code for an altered protein with a different shape. An enzyme’s active sight my no longer have a shape complementary to a specfic substrate or a structural protein may lose its strength.

Question 27

How can the chance of a mutation increase

Answer 27

Exposure to certain substances or some types of radiation eg X rays or smoking

Question 28

How do most muations effect the protiens

Answer 28

Most do not alter the protein, or only alter it slightly so that its appearance or function is not changed.

Question 29

What would the mutation of a non- coding gene cause

Answer 29

Not all parts of DNA code for proteins. Non-coding parts of DNA can switch genes on and off, so variations in these areas of DNA may affect how genes are expressed

Question 30

Explain inseertion deletion and substitution mutations…

Answer 30

Insertion - when new bases are inserted into the DNA base sequence where it should be
(Changes the way which three bases are read changing the coded for amino acid and has effects further down the sequence)

Deletion - a random base is delted from the DNA sequence. (Like insertions they effect the way the base sequence is read and have knock on effects further down the sequence)

substitution - where a random base in the DNA sequence is changed to a different base

Question 31

Haploid is the quality of a cell or organism having a single set of chromosomes.

Answer 31

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