Topic 6-Inheritance, Variation and Evolution

Question 1

What is sexual reproduction?

Answer 1

It involves the joining of male and female gametes, each containing genetic information from the mother or father

A gamete from each parent fuses to form a zygote and genetic information from each gamete is mixed so the resulting zygote is unique

Question 2

What are gametes?

Answer 2

Sex cells (sperm and egg cells in animals, pollen and egg cells in flowering plants)

Haploid (half the number of chromosomes)

Question 3

How many chromosomes does a normal cell have?

Answer 3

46

Question 4

What is asexual reproduction?

Answer 4

Involves only one parent (no gametes joining)

Happens only using the process of mitosis

No genetic variation and leads to clones (genetically identical to each other and the parent)

eg bacteria, some plants and some animals

Question 5

What must occur prior to meiosis?

Answer 5

Interphase-copies of genetic information are made during this process

Question 6

What happens during the first stage of meiosis?

Answer 6

Chromosome pairs line up along the cell equator

The pair of chromosomes are separated and move to opposite poles of the cell (the side to which each chromosome is pulled is random, creating variation)

Chromosome number is halved

Question 7

What happens during the second stage of meiosis?

Answer 7

Chromosomes line up along the cell equator

The chromatids are separated and move to opposite poles of the cell

Four unique haploid gametes are produced

Question 8

Why is meiosis important for sexual reproduction?

Answer 8

It increases genetic variation

It ensures that the zygote formed at fertilisation is diploid

Question 9

Describe fertilisation and its resulting outcome

Answer 9

Gametes join at fertilisation to produce a cell with 46 chromosomes, the normal number

This cell divides by mitosis to produce many copies

More and more cells are produced and an embryo forms

The cells begin to take on different roles after this stage (differentitation)

Question 10

What does the term haploid mean?

Answer 10

When the nuclei only contain one set of chromosomes each

Question 11

What does the term diploid mean?

Answer 11

When the nuclei contain two sets of chromosomes

Question 12

What does DNA stand for?

Answer 12

Deoxyribonucleic acid

Question 13

What is DNA?

Answer 13

A double-stranded polymer of nucleotides, wound to form a double helix

The genetic material of the cell in found in its nucleus

Question 14

What is each nucleotide made up of?

Answer 14

One sugar molecule, one phosphate molecule (forms backbone) and one of the four types of organic bases

Question 15

Define genome

Answer 15

The entire genetic material of an organism

Question 16

What are the four types of organic bases?

Answer 16

A, C, G, T

Question 17

Why is understanding the human genome important?

Answer 17

The whole human genome has been studied and is important for the development of medicine in the future

-Searching for genes linked to different types of disease

• Understanding and treating inherited disorders
• Tracing human migration patterns from the past

Question 18

What is a chromosome?

Answer 18

A long, coiled molecule of DNA that carries genetic information in the form of genes

Question 19

Define gene

Answer 19

A small section of DNA that codes for a specific sequence of amino acids which undergo polymerisation to form a protein

Question 20

Describe how nucleotides interact to form a molecule of DNA

Answer 20

Sugar and phosphate molecules join to form a sugar-phosphate backbone in each DNA strand

Base connected to each sugar

Complementary base pairs (A pairs with T, C pairs with G) joined by weak hydrogen bonds

Question 21

Explain how a gene codes for a protein

Answer 21

A sequence of three bases in a gene forms a triplet

Each triplet codes for an amino acid

The order of amino acids determines the structure and function of protein formed

Question 22

Describe the process of meiosis

Answer 22

The cell makes copies of its chromosomes, so it has double the amount of genetic information

The cell divides into two cells, each with half the amount of chromosomes (46)

The cell divides again producing four cells, each with a quarter the amount of chromosomes (23)

These cells are called gametes and they are all genetically different from each other because the chromosomes are shuffled during the process, resulting in random chromosomes ending up in each of the four cells

Question 23

Why is the ‘folding’ of amino acids important in proteins such as enzymes?

Answer 23

The folding of amino acids determines the shape of the active site which must be highly specific to the shape of its substrate

Question 24

What is protein synthesis?

Answer 24

The formation of a protein from a gene

Question 25

What are the two stages of protein synthesis?

Answer 25

Transcription

Translation

Question 26

What does transcription involve?

Answer 26

The formation of mRNA from a DNA template

Question 27

Outline translation

Answer 27

DNA double helix unwinds

RNA polymerase binds to a specific base sequence of non-coding DNA in front of a gene and move along the DNA strand

RNA polymerase joins free RNA nucleotides to complementary bases on the coding DNA strand

mRNA formation complete. mRNA detaches and leaves the nucleus

Question 28

What is the process of protein synthesis?

Answer 28

The process of producing a protein from DNA

Question 29

What are alleles?

Answer 29

Forms of a gene

Question 30

Where is DNA found in a human cell?

Answer 30

In the chromosomes in the nucleus

Question 31

What is a dominant allele?

Answer 31

It is an allele expressed even when other allele are present

Question 32

Which bases pair up?

Answer 32

A T

C G

Question 33

Strand K shows a mutation in the DNA which has caused syndrome H

The enzyme IDUA helps to break down a carbohydrate in the human body

The enzyme IDUA produced from Strand K will not work

Explain how the mutation could cause the enzyme not to work

Answer 33

Mutation changes from C to T DNA code

This changes the amino acid

This would change the protein

So it forms a different shape/changed active site

The enzyme no longer fits the substrate

Question 34

Why is DNA describes as a polymer?

Answer 34

They are made up of repeated units of nucleotides

Question 35

Some parts of DNA do not code for proteins

Describe how non-coding parts of DNA can affect the expression of genes

Answer 35

Non-coding parts can switch genes on/off

Question 36

There are two types of cell division: mitosis and meiosis

Describe three differences between the processes of mitosis

Answer 36

One cell division in mitosis and two cell divisions in meiosis

Mitosis produces two cells but meiosis produces four daughter cells

Mitosis produces genetically identical cells, but meiosis produces genetically different cells

Mitosis produces diploid cells but meiosis produces haploid cells

Question 37

Describe one similarity between the processes of mitosis and meiosis

Answer 37

Increase in the number of mitochondria/ribosomes/sub-cellular structures

DNA replicates

Question 38

Syndrome H is an inherited condition

People with syndrome H do not produce the enzyme IDUA

A mutation in the DNA causes syndrome H

The enzyme IDUA helps to break down a carbohydrate in the human body

The enzyme IDUA pduced from someone who has the mutation will not work

Explain how the mutation could cause the enzyme not to work

Answer 38

Mutation causes a change the in three bases

This changes the protein so it forms a different shape and changes the active site

Therefore the enzyme no longer fits the substrate

Question 39

What is an allele?

Answer 39

They are one form of a gene

Question 40

What are some advantages of embryo screening?

Answer 40

It prevents future suffering

Embryos could be used for stem cell treatment

Stops baby from inheriting disease

Question 41

What are some objections to embryo screening?

Answer 41

Could cause a miscarriage

May lead to damage of embryo

Prejudice against disabled people

Question 42

When a cell divides by mitosis, the new cells are genetically identical

What causes the cells to be genetically identical?

Answer 42

The DNA/chromosomes are replicated

Question 43

Describe how embryos can be screened for the alleles that cause genetic disorders

Answer 43

DNA isolated from embryo

Fluorescent probe is mixed with DNA

Probe then binds with embryo DNA

Use of UV light to show alleles/gene for disorder

Question 44

The sequence of compounds A, C, G and T in the gene is important

Explain why.

Answer 44

The order of three bases codes for a specific protein