Paper 1 - Topic 3, Genetics

Question 1

What type of cells does sexual reproduction produce

Answer 1

Genetically different cells

Question 2

What is produced in sexual reproduction

Answer 2

Gametes, sperm and egg cells

Question 3

What do gametes contain

Answer 3

Half the number of chromosomes of normal cells - haploid cells

Question 4

What happens at fertilisation

Answer 4

A male gamete fuses with a female gamete to produce a fertilised egg

Question 5

What is a fertilised egg called

Answer 5

A zygote

Question 6

How does a zygote develop into an embryo

Answer 6

Cell division by mitosis

Question 7

How many chromosomes does a human cell contain

Answer 7

46

Question 8

Where are the male gametes found in flowers

Answer 8

The pollen

Question 9

Where are the female gametes found in flowers

Answer 9

In the ovaries at the bottom of a stigma

Question 10

How is meiosis different to mitosis

Answer 10

Meiosis produces genetically different cells, meiosis only happens in the reproductive organs

Question 11

Describe division 1 of meiosis

Answer 11

1. It duplicates its DNA, one arm of each X-chromosome is an exact copy of the other arm
2. The chromosomes then line up in centre of cell, one chromosome in each pair came from the mother and one from the father
3. The pairs are pulled apart so each new cell has one copy of each chromosome, some of the mothers and father’s chromosomes in each new cell
4. Each new cell has mixture of mothers and fathers chromosomes, mixing up genes creates genetic variation in offspring

Question 12

Describe division 2 in meiosis

Answer 12

1. The chromosomes line up again in centre of cell, the arms of the chromosomes are pulled apart
2. You then get four haploid daughter cells, these are gametes, each gamete has a single set of chromosomes, the gametes are genetically different

Question 13

What happens if something reproduces asexually

Answer 13

• divide by mitosis
• results in two diploid daughter cells
• they are genetically identical to each other and the parent

Question 14

What happens if something reproduces sexually

Answer 14

• meiosis
• produces genetically different haploid gametes which fuse to form a diploid cell at fertilisation

Question 15

What are the advantages of asexual reproduction

Answer 15

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

Question 16

What are disadvantages of asexual reproduction

Answer 16

• no genetic variation so if environment changes and conditions become unfavourable, whole population may be affected

Question 17

What are the advantages of sexual reproduction

Answer 17

• creates genetic variation within population so individuals have different characteristics and if environment changes its more likely some individuals will survive the change

Question 18

What are the disadvantages of sexual reproduction

Answer 18

• takes more time and energy, so less offspring are created in an organisms lifetime (need to attract mates which takes time and energy
• two parents are need so if individuals are isolated it can be a problem

Question 19

What do nucleotides consist of

Answer 19

A sugar, a phosphate and one base

Question 20

What does the sugar and phosphate create

Answer 20

The backbone

Question 21

What are DNA strands

Answer 21

Polymers made up of lots of repeating units called nucleotides

Question 22

What are the four bases called

Answer 22

Adenine
Thymine
Cytosine
Guanine

Question 23

What are the complementary base pairs joined together by

Answer 23

Weak hydrogen bonds

Question 24

Where are chromosomes found

Answer 24

In the nucleus of a eukaryotic cell

Question 25

What is a gene

Answer 25

A section of DNA on a chromosome that codes for a particular protein

Question 26

How do you extract DNA from fruit cells

Answer 26

1. Mash strawberries and put in beaker containing a solution of detergent and salt and mix 2. Filter mixture to get the froth and big insoluble cells out 3. Add ice cold alcohol to filtered mixture 4. DNA will start to come out solution as not soluble in cold alcohol, appears as stringy white precipitate

Question 27

What will the detergent salt solution do in the DNA extraction from fruit cells experiment

Answer 27

Detergent: break down the cell membranes to release DNA Salt: make DNA stick together

Question 28

What are proteins made up of

Answer 28

Amino acids

Question 29

What do the order of bases in a gene determine

Answer 29

The order of amino acids in a protein

Question 30

How is each amino acid coded

Answer 30

By a sequence of three bases in a gene

Question 31

What is a mutation

Answer 31

A rare ,random change to an organisms DNA base sequence that can be inherited

Question 32

What happens if a mutation happens in a gene

Answer 32

Produces a genetic variant

Question 33

Where are proteins made

Answer 33

In the cell cytoplasm by ribosomes

Question 34

What is mRNA

Answer 34

Messenger RNA, a polymer of nucleotides which is short and single stranded and uses Uracil instead of Thymine

Question 35

What is RNA polymerase

Answer 35

The enzyme involved in joining together RNA nucleotides to make mRNA

Question 36

How does transcription work

Answer 36

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 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 moves out of the nucleus and joins with a ribosome

Question 37

How does translation work

Answer 37

1. Amino acids are brought to ribosomes by another RNA molecule called transfer RNA (tRNA) 2. The order in which amino acids are brought to ribosomes matches the order of base triplets in the mRNA (base triplets called codons) 3. Part of the tRNA structure in an anticodon which is complementary to the codon for the amino acid, the paring of the codon and anti-codon make sure amino acids are brought to ribosome in correct order 4. The amino acids are joined together by ribosome which makes polypeptide