Topic 3 - Genetics

Question 1

Sexual reproduction

Answer 1

Genetic information of 2 organisms is combined to produce offspring which are genetically different to either parent,

Question 2

Gametes

Answer 2

Reproductive cells: sperm and egg -haploid (23 chromosomes)

Question 3

Fertilisation

Answer 3

The gametes fuse to produce a fertilised egg known a zygote. The zygote has a full set of chromosomes. The zygote then undergoes cell division to form an embryo

Question 4

Embryo characteristics

Answer 4

Inherits characteristics from both parents as it received a mixture of chromosomes (therefore genes).

Question 5

Production of gametes

Answer 5

Meiosis

Question 6

Meiosis

Answer 6

Produces haploid cells which aren’t genetically identical. Only occurs in reproductive organs.

Question 7

Meiosis Division 1

Answer 7

Cell duplicates DNA forming an X-Shaped chromosome. Chromosomes line up at equator. One chromosome from each pair came from the organisms mother and the other from the father. The pairs are pulled apart. Each new cell with have a mixture of the mother’s and father’s chromosomes. This mixture allows for genetic variation.

Question 8

Meiosis Division 2

Answer 8

Chromosomes line up, arms of chromosomes are pulled apart. 4 haploid daughter cells are produced these are gametes, all genetically different.

Question 9

Asexual reproduction

Answer 9

Using mitosis to produce genetically identical cells.

Question 10

Sexual reproduction process

Answer 10

Meiosis resulting in genetically different haploid gametes which fuse to form a diploid cell at fertilisation.

Question 11

Advantages of asexual reproduction

Answer 11

Produces lots of offspring very quickly as for short reproductive cycle. Eg. Bacteria - E. coli.
This allows them to populate and colonise areas very rapidly.

Only one parent is required so can reproduce when conditions are favourable eg. Aphids in the summer when food is plentiful

Question 12

Sexual reproduction advantages

Answer 12

Creates genetic variation allowing different characteristics meaning if conditions change some individuals will have the characteristics to survive. This is natural selection and evolution.

Question 13

Asexual reproduction disadvantages

Answer 13

No genetic variation. So if environment changes the whole population is vulnerable. Eg. Black Sigatoka is a disease affecting banana plants. All banana species are vulnerable.

Question 14

Sexual reproduction disadvantages

Answer 14

Takes more time and energy so fewer offspring are produced in lifetime because mates must be found requiring energy and time. Eg. Male Bowerbirds build structures of twigs to impress females.

2 parents are needed for sexual reproduction, if an individual is isolated this is an issue. Eg. Polar Bears are independent and may walk 100 miles to find a mate.

Question 15

Nucleotide

Answer 15

The monomer of DNA

Question 16

DNA structure

Answer 16

A double helix sugar-phosphate backbone with complimentary nucleotides connected with a weak hydrogen bonds.

Question 17

Base pairs

Answer 17

Adenine -> Thymine

Cytosine -> Guanine

Question 18

Chromosomes

Answer 18

Long coiled up molecules of DNA. Found in the nucleus of eukaryotic cells.

Question 19

Gene

Answer 19

Section of DNA which codes for a certain protein

Question 20

Genome

Answer 20

All the DNA of an organism

Question 21

Extract DNA

Answer 21

Mash the fruit.
Add:
Detergent - break down nucleus
Salt - Makes DNA stick together

Filter the mixture and remove froth and insoluble bits.
Add ice-cold ethanol to draw out the DNA as its not soluble in alcohol. A white precipitate will form. Remove with glass rod,

Question 22

DNA controls

Answer 22

The production of proteins

Question 23

Proteins are made up of

Answer 23

Amino acids in a polypeptide chain. They can have different orders and have a specific shape which defines its function.

Question 24

Base triplet

Answer 24

Each amino acid is coded in a sequence of 3 bases in the gene (DNA)

Question 25

Non-coding regions

Answer 25

Don’t code for any amino acids although still involved in protein synthesis.

Question 26

Genome

Answer 26

All DNA within an organism including non-coding.

Question 27

Genetic variation by mutation

Answer 27

If a mutation happens in a gene it can code for a different sequence of amino acids therefore proteins. This effects the phenotype, it may be positive or negative. Can also occur in non-coding regions.

Question 28

Ribosomes

Answer 28

Make proteins in the cytoplasm

Question 29

Transcription

Answer 29

1. RNA polymerase (enzyme) binds to the non-coding DNA.
2. RNA polymerase unzips the DNA and moves along the strands of DNA placing mRNA.
3. Coding DNA is used as a template. Base pairings ensure mRNA is complimentary to the gene.
4. Once a stop gene is reached the mRNA moves out of nucleus and joins with Ribosomes.

Question 30

Purpose of transcription

Answer 30

DNA found in the nucleus (as it’s so big) must pass over genetic material to ‘ribosomes’ to construct proteins. ‘Messenger RNA’ is used (single strand and shorter). ‘Uracil’ is used instead of ‘thymine’.

Question 31

Translation

Answer 31

1. Amino acids brought to the ribosome by tRNA.
2. tRNA has an ‘anticodon’ which is complimentary for the amino acid. This ‘anticodon’ on the tRNA (acts as the original coding side) matches the base triplet on the mRNA. This pairing ensures amino acids are in the correct order.
3. Amino Acids are joined together with a peptide bond forming a polypeptide chain (protein)

Question 32

Transcription and mutation

Answer 32

If a mutation occurs on the non-coding side it can affect RNA polymerase’ ability to bind to it. This affects how much is transcribed therefore how much protein is produced affecting the end phenotype.

Question 33

Mendel’s experiment

Answer 33

1. Mendel crossed 2 pea plants of different heights
   -tall pea and -dwarf pea
   The offspring all produced were ALL TALL PEA
2. He bred 2 of these tall offspring together (from the last generation) and 3 tall pea plants were produced for every 1 dwarf pea plant.

T - Dominant - Tall
t - recessive - dwarf

Question 34

Mendel’s 3 conclusions

Answer 34

1. Characteristics were determined by “hereditary units” (genes).
2. Hereditary units are passed on to the offspring unchanged from both parents.
3. Hereditary units can be dominant or recessive.

Question 35

Mendel’s work in society

Answer 35

He was cutting edge and took time for people to understand his work.
It is now understood today that “hereditary units” are genes but scientists at the time didn’t know of DNA or genes.
His work wasn’t significant until after his death that he explained the mechanism of inheritance.