genetics and reproduction P2

Question 1

Sexual reproduction

Answer 1

Meiosis

• 2 parents needed
• fusion of male and female gametes to create a zygote (fertilized egg)
• offspring produced is genetically different
• mixing of genetic information
• chromosomes are halved (23)
• divides twice

Question 2

Asexual reproduction + examples

Answer 2

Mitosis

• involves only one individual
• offspring is genetically identical to parent
• no fusion of gametes or mixing of genetic information

= aphids, buds

Question 3

Zygote

Answer 3

a fertilized egg

Question 4

Mitosis + uses

Answer 4

1) nucleus with 46 chromosomes in
2) DNA replication and cell growth;
chromosomes copied (and everything else in cell), nuclear membrane breaks down
3) Mitosis; chromosomes and copies pulled apart and moved towards poles
4) Cell division; cell divides into two genetically identical daughter cells

-uses of mitosis; growth, repair of damaged tissues, replacement of worn out cells

Question 5

Gamete

Answer 5

A sex cell (egg, sperm)

Question 6

DNA structure

Answer 6

DNA is a polymer made up of two twisted ladder structures called the double helix.
DNA is found in the chromosomes in the nucleus of an organism.
It is our genetic material which determines our inherited features.

DNA is a polymer of molecules called nucleotides (3 parts, phosphate group attached to sugar molecule, attached to a base) —> only base changes

Bases : ACGT -> DNA contains 4 nucleotides
DNA strands are complementary as the same bases always pair on the opposite strands.

Question 7

Gene

Answer 7

A small section of DNA on a chromosome

Question 8

Genome

Answer 8

The entire genetic material of an organism

Question 9

Why is it important to understand the human genome? (benefits)

Answer 9

1) Helps us understand and treat inherited diseases (e.g cystic fibrosis)
2) Helps us to search for genes that are linked to a disease (e.g genes that increase the risk of developing cancer).
3) Can use human genome to trace human migration patterns from the past —> helps with understanding ancestory

Question 10

What does it mean when saying DNA strands are complementary?

Answer 10

Means that same bases always pair on the opposite strands.
C-G
A-T

Question 11

Protein Synthesis

Answer 11

1) Takes place in nucleus, Transcription -> Base sequence of gene is copied into a complementary template molecule called the messenger RNA ( a single stranded molecule)

mRNA now passes out of nucleus and into cytoplasm

2) Takes place in cytoplasm, Translation ->
- mRNA molecule attaches to a ribosome
- amino acids are brought to ribosome on carrier molecules, called transfer RNA
- ribosome reads the triplets of bases on mRNA and uses this to bind the correct amino acids in the right order
- once protein chain is complete, folds out into its unique shape for its specific job

Question 12

nucleotide

Answer 12

a monomer (single unit) of DNA 
(consists of phosphate, sugar and base)

Question 13

Amino acids

Answer 13

-what makes up proteins

a group of 3 bases codes for an amino acid ( TAG or CTA or TGC)

Question 14

Chromosome

Answer 14

Long threads of DNA , which are made up of many genes (contains the DNA)

Question 15

haploid

Answer 15

a cell that contains a single set of chromosomes (e.g a gamete)

Question 16

diploid

Answer 16

a cell that contains the full 23 chromosome pairs (e.g a human cell)

Question 17

fertilisation

Answer 17

fusion of female and male gametes

=in fertilisation cells restore the full normal amount of chromosomes (opposite to meiosis)

Question 18

meiosis

Answer 18

Takes place in reproductive organs (testes, ovaries)
-sexual reproduction

1) chromosomes in human reproductive organ are copied
2) cell divides into two
3) cell divides again to from 4 gametes which contain single chromosomes (not paired)
4) these gametes contain half the amount of chromosomes (23) so that when fertilisation occurs, it restores the normal amount of 46

• meiosis halves the amount of chromosomes
• produces 4 gametes from one cell
• all 4 gametes are GENETICALLY DIFFERENT

Question 19

how many amino acids are there in a human?

Answer 19

20

Question 20

order of amino acids

Answer 20

The specific order of an amino acid determines its shape and function.
The order of amino acids in a protein is determined by the sequence of bases in the gene.

Question 21

what is a mutation

Answer 21

a change in a base

- they happen all the time

Question 22

ineffective mutation

Answer 22

A single base in a sequence changes (mutation occured) but amino acid has not changed the sequence. This is because different base triplets can encode for the same amino acid . So in this case the mutation has had no effect.
= most mutations are ineffective and happen frequently

Question 23

effective mutation

Answer 23

A single base in a sequence changes (mutates) and the amino acid changes and this change has altered the shape and function of protein.
= could lead to the active site changing so the substrate no longer fits

Question 24

chromosomes also contain non-coding parts of DNA + mutation

Answer 24

These regions switch genes on and off. This means they tell genes when to produce proteins.
Mutations in these regions can affect how the gene is switched on and off (e.g a gene may be turned on when it should be off. In this case, the cell would produce a protein that was not needed at that time). –> uncontrolled mitosis leading to cancer

Question 25

where is dna found

Answer 25

in chromosomes

Question 26

alleles

Answer 26

different versions of the same gene

Question 27

genotype

Answer 27

refers to the combination of alleles an organism has ( BB, bb, Bb)

Question 28

homozygous

Answer 28

two copies of the SAME allele (EE) or (ee)

Question 29

phenotype

Answer 29

tells us the physical characteristics caused by the persons alleles
(e.g two alleles for dry ear wax ee = phenotype is dry ear wax)

Question 30

heterozygous

Answer 30

two DIFFERENT alleles ( Ee)

Question 31

dominant alleles

Answer 31

capital letter

- will show in the phenotype even if there is only one copy (e.g Ee)

Question 32

recessive alleles

Answer 32

lower case letter

= must be two copies to be shown in phenotype (ee) not (Ee)

Question 33

cystic fibrosis , what is it?

Answer 33

An inherited disorder of the cell membranes in the lungs. Abnormally thick mucus.

• recessive allele (must have two recessive alleles to have it)
• can be a carrier

Question 34

carrier

Answer 34

someone who can pass a disease onto their children but they are healthy
someone who can pass a disease onto their children but if a person has 1 of each allele (heterozygous) they are a carrier

Question 35

can you be a carrier of a disease caused by a dominant allele?

Answer 35

NO - because dominant alleles are expressed even if there is only one.

Question 36

Polydactyly

Answer 36

An inherited disease which causes extra toes/fingers.

- caused by a dominant allele, cannot be a carrier

Question 37

solutions for inherited diseases?

Answer 37

embryo screening - embryos are tested to see if they possess the alleles for inherited disorders. If they do not then they are implanted into the women to produce healthy offspring. (form of genome screening)

Question 38

advantages and disadvantages of embryo screening

Answer 38

disadvantages ->

• ethical issues as embryo cannot give consent/often loads of a embryos are tested those that are not (although perfectly healthy) are destroyed.
• expensive
• parents become selective -> technology could allow parents to chose the most desirable embryo

advantages ->

• prevents suffering of offspring with genetic disorders
• financial saving (less people with inherited diseases, less money on treatment, better in long-term)

Question 39

cystic fibrosis : CC , Cc, cc meaning

Answer 39

CC -> not affected
Cc -> carrier
cc-> affected

Question 40

polydactyly: PP, Pp , pp meaning

Answer 40

PP -> affected
Pp -> affected
pp -> not affected

Question 41

what do family trees show/not show

Answer 41

they show the phenotype NOT the genotype

Question 42

vector

Answer 42

transfering DNA from one organism to another

Question 43

Genetic Engineering

Answer 43

1) Identify the gene you want to transfer (e.g human gene or plant gene)
2) Use enzymes to isolate this gene
3) Transfer gene into a plasmid or a virus (vector : transfers dna from one organism to another)
4) Desired gene is transferred into the cells of the target organism (idea is that the organisms cells will take up the vectors, and the useful gene inside it, to produce the protein that the gene codes for)

(always transfer a gene at the early stage in the organisms development = to make sure all cells recieve the transferred gene, so develops with the desired characteristics)