B3 - Genetics

Question 1

What is

sexual reproduction?

Answer 1

where genetic information from two organisms is combined to produce offspring which are genetically different to either parent

Question 2

What are

gametes?

Answer 2

the reproductive cells that are produced by the mother and father in sexual reproduction

these are haploid - they contain half the number of chromosones of normal cells

Question 3

What occurs during

fertilisation?

Answer 3

a male gamete fuses with a female gemate to produced a fertilised egg, also known as a zygote

Question 4

What is

meiosis?

Answer 4

a type of cell division which doesn’t produce identical cells

(in humans, this only happens in the reproductive organs)

Question 5

Describe the process of

meiosis.

(6 steps)

Answer 5

1. The cell duplicates its DNA.
2. In the first division, the chromosones line up in pairs in the centre of the cell - one chromosone in each pair came from the organism’s mother and one came from its father.
3. The pairs are then pulled apart, so each new cell only has one copy of each chromosone - some of the father’s chromosones and some of the mother’s chromosones go into each new cell.
4. In the second division the chromosones line up again in the centre of the cell.
5. The arms of the chromatids are pulled apart.
6. Four haploid daughter cells - called gametes are produced.

Each gamete only has a single set of chromosones. The gametes are all genetically different.

Question 6

What are some advantages of

asexual reproduction?

(2, explained)

Answer 6

• can produce lots of offspring very quickly because the reproductive cycle is so fast - so organisms can colonise a new area very rapidly
• only one parent is needed - so organisms can reproduce whenever conditions are favourable, without having to wait for a mate

Question 7

What is an advantage of

sexual reproduction?

Answer 7

Sexual reproduction creates genetic variation within the population, meaning that different individuals have different characteristics.

This means that if the environmental conditions change, it’s more likely that at least some individuals in the population will have the characteristics to survive the change.

Over time, this can lead to natural selection and evolution.

Question 8

What is the disadvantage of

asexual reproduction?

Answer 8

There’s no genetic variation between offspring in the population.

So, if the environment changes and conditions become unfavourable, the whole population may be affected.

Question 9

What are some disadvantages to

sexual reproduction?

(2)

Answer 9

• it takes more time and energy than asexual reproduction, so organisms produce fewer offspring in their lifetime
• it requires two parents, which can become a problem if individuals are isolated

Question 10

What are

DNA strands?

Answer 10

polymers made up of lots of repeating units called nucleotides

Question 11

What do

nucleotides consist of?

Answer 11

a sugar and a phospohate group - forming the ‘backbone’ of DNA strands - and a ‘base’

Question 12

What are the

four bases that make up nucleotides?

(and join to each sugar) and what are the complementary pairs of these?

Answer 12

adenine, thymine, cytosine and guanine

A + T, C + G

Question 13

What does a

DNA molecule consist of?

Answer 13

two DNA strands coiled together in the shape of a double helix

each base links to another base on the opposite strand in the helix

Question 14

How are the

complementary base pairs joined together?

Answer 14

weak hydrogen bonds

Question 15

What are

chromosones?

and where are they found?

Answer 15

long, coiled up molecules of DNA

they’re found in the nucleus of eukaryotic cells

Question 16

Define

gene.

Answer 16

a section of DNA on a chromosone that codes for a particular protein

Question 17

What is a

genome?

Answer 17

all of an organism’s DNA

Question 18

Describe an experiment to

extract DNA from fruit cells.

(5 steps)

Answer 18

1. Mash some strawberries and then put them in a beaker containg a solution of detergent and salt.
2. Mix well - the detergent will break down the cell membranes to release the DNA, the salt will make the DNA stick together.
3. Filter the mixture to get the froth and big, insoluble bits of cell out.
4. Gently add some ice-cold alcohol to the filtered mixture.
5. The DNA will start to come out of solution as it is not soluble in cold alcohol. It will appear as a stringy white precipitate that can be carefully fished out with a glass rod.

Question 19

What does

DNA do?

Answer 19

controls the production of proteins in a cell

this process is called protein synthesis

Question 20

What are

proteins made of?

Answer 20

chains of molecules called amino acids

Question 21

Define

base triplet.

Answer 21

the sequence of three bases that code for each amino acid in the gene

Question 22

What is a

non-coding region of DNA?

Answer 22

a region of DNA that doesn’t code for any amino acids

Question 23

Define

mutation.

Answer 23

a rare, random change to an organism’s DNA base sequence that can be inherited

Question 24

Where are

proteins made?

Answer 24

in the cell cytoplasm by subcellular structures called ribosomes

Question 25

# What is messenger RNA (mRNA)? | and how is this different to DNA?

Answer 25

a **polymer** of **nucleotides** ## Footnote it is **shorter** than DNA and only a **single strand** it also uses **uracil** (U) instead of **thymine** (T) as a **base**

Question 26

# What is RNA polymerase?

Answer 26

the **enzyme** involved in **joining together** RNA nucleotides to make mRNA

Question 27

# Why is transcription necessary for making proteins?

Answer 27

DNA found in the cell **nucleus** can't move out of it because it is **really big**, however, the cell still needs to get the information from the DNA to the ribosome in the cytoplasm.

Question 28

# What are the two stages of protein synthesis?

Answer 28

1. Transcription 2. Translation

Question 29

# Describe the process of transcription. | (4 steps)

Answer 29

1. **RNA polymerase** binds to a region of **non-coding DNA** in front of a gene. 2. The two DNA strands **unzip** and the RNA polymerase **moves along** one of the strands of the DNA. 3. It uses the **coding DNA** in the **gene** as a **template** to make the **mRNA**. (**Base pairing** between the DNA and RNA ensures that the mRNA is **complementary** to the gene.) 4. Once made, the mRNA molecule moves **out** of the nucleus and joins with a **ribosome**.

Question 30

# What is a codon?

Answer 30

a base triplet of mRNA

Question 31

# What is an anticodon?

Answer 31

the **complementary** tRNA to the codon

Question 32

# Describe the process of translation. | (4 steps)

Answer 32

1. **Amino acids** are brought to the **ribosome** by another RNA molecule called **transfer RNA** (**tRNA**). 2. The tRNA **anticodons** bind to their complementary codons, making sure that the amino acids are brought to the ribosome in the **correct order**. 3. The amino acids are **joined together** by the ribosome to make a **polypeptide** (protein). 4. The amino acid chains **fold up** to give each protein a **different**, **specific shape**.

Question 33

# How can a mutation in the non-coding region of DNA affect the production of the protein? | (3 points)

Answer 33

- Before any transcription can happen, **RNA polymerase** has to bind to a region of non-coding DNA **in front** of a gene. - If a **mutation** happens in this region of DNA, then it could affect the **ability** of the polymerase to bind to it. This might make it **easier** to bind to, or **more difficult**. - How well RNA polymerase binds to this region of DNA will affect **how much** mRNA is **transcribed** - therefore how much **protein** is **produced**

Question 34

# What were the three important conclusions about heredity in plants that Gregor Mendel came to?

Answer 34

1. Characteristics in plants are determined by '**hereditary units**'. 2. Hereditary units are passed on to offspring **unchanged** from both parents, **one unit** from **each parent**. 3. Hereditary units can be **dominant** or **recesive**.

Question 35

# Why wasn't the importance of Mendel's work recognised straight away?

Answer 35

At the time, scientists didn't have the background knowledge to **properly understand** Mendel's findings - they didn't know about **genes**, **DNA** or **chromosones**.

Question 36

# Define allele.

Answer 36

a **different version** of the **same gene**

Question 37

# When is an organism homozygous? | (for a trait)

Answer 37

when it has **two alleles** for a particular gene that are **the same**

Question 38

# When is an organism heterozygous? | (for a trait)

Answer 38

when it has two **different** alleles for a particular gene that are **different**

Question 39

# Define genotype.

Answer 39

the combination of **alleles** you have

Question 40

# Define phenotype.

Answer 40

the characteristics you have | (based on your genotype)

Question 41

# How many chromosone pairs does each human body cell have?

Answer 41

23 | matched pairs

Question 42

# What human chromosone determines gender?

Answer 42

the **23rd pair** | these are labelled **XX** or **XY** ## Footnote **Y** chromosone causes **male** characteristics the **XX combination** allows for **female characteristics** to develop

Question 43

# Define sex-linked genetic disorder.

Answer 43

a disorder causes by a **faulty allele** located on **sex chromosones**

Question 44

# Why are men more likely to have sex-linked genetic disorders? | (3 steps)

Answer 44

1. The **Y chromosone** is **smaller** than the X chromosone and carries **fewer genes**. So, **most genes** on the sex chromosones are **only** carried on the **X chromosone**. 2. **Males** only have **one X chromosone**, so only have **one allele** for sex-linked genes. 3. This means that the **characteristic** of this allele is **shown**, even if it is **recessive**.

Question 45

# What are codominant alleles?

Answer 45

alleles where one isn't dominant over the other one

Question 46

# Describe how alleles determine blood group. | (4 steps)

Answer 46

1. Humans have **four** potential **blood types** - **O**, **A**, **B** and **AB**. 2. The **gene** for blood type in humans has **three different alleles** - IO, IA, IB. 3. **IA** and **IB** are **codominant** with eachother, so an individual with genotype IAIB will have the blood type **AB**. 4. **IO** is **recessive** so you only get **blood type O** when you have **two of the recessive alleles**.

Question 47

# How is there genetic variation within a species? | (2 ways)

Answer 47

- **new alleles** arising through **mutations** - **sexual reproduction** resulting in alleles being **combined** in lots of **different ways** in offspring

Question 48

# What are the environmental variations in a phenotype?

Answer 48

the characteristics that organisms acquire during their lifetimes | (their acquired characteristics)

Question 49

# What are neutral mutations?

Answer 49

mutations that don't have **any effect** on the **phenotype** of an organism

Question 50

# What are some general medical applications of the genome project's research? | (3)

Answer 50

- prediction and prevention of diseases - testing and treatment for inherited disorders - new and better medicines

Question 51

# How can the genome project's research predict and prevent diseases? | (3 points)

Answer 51

- Many **common diseases** are caused by the **interaction** of **different genes** (as well as **lifestyle factors**) - If doctors knew **what genes** redisposed people to **what diseases**, we could all get **individually tailored** advice on the best diet and lifestyle to avoid our likely problems - Doctors could also **check us** regularly to ensure **early treatment** if we do develop the diseases we're susceptible to

Question 52

# How can the genome project's research test and treat for inherited disorders? | (3 points)

Answer 52

- inherited disorders are caused by the presence of one or more **faulty genes** in a person's genome - scientists are now able to **identify** the genes and alleles that are suspected of causing an inherited disorder **much more quickly** - once such an allele has been identified, people can be **tested** for it ## Footnote this may make it possible to **develop better treatments** or even develop a **cure** for the disease

Question 53

# How can the genome project's research help to create new and better medicines? | (4 points)

Answer 53

- the research has highlighted some **common genetic variations** between people - some variations affect how our individual bodies will **react** to certain **diseases** and to the possible **treatments** for them - this knowledge can be used to **design new drugs** that are specifcally tailored to people with a **particular genetic variation** - the knowledge can also determine **how well an existing drug will work** for an individual - also, knowing how a disease affects us on a **molecular level** should make it possible to design **more effective** treatments with **fewer side-effects**

Question 54

# What are some drawbacks of the medical applications of the genome project? | (3 points, briefly explained)

Answer 54

1. **Increased stress** - if someone knew that they're susceptible to a certain disease, they may **panic** every time they get a symptom (even if they never get the disease). 2. **Gene-ism** - people with genetic problems could come under **pressure** to not have children. 3. **Discrimination** - **life insurance** could be harder and more expensive to get if you have any **genetic likelihood** of serious disease. Also, employers may **discriminate** against people who are genetically likely to get a disease.