Genetics

Question 1

what is sexual reproduction?

Answer 1

-where genetic information from two organisms is combined to produce genetically different offspring

Question 2

What are gametes?

Answer 2

-reproductive cells produced by the mother and father
-only contain half the number of chromosomes - they are haploid

Question 3

what is fertilisation?

Answer 3

-when the male gamete fuses with a female gamete to produce a fertilised egg (zygote)
-zygote is diploid and ends up with the full set of chromosomes

Question 4

What is an embryo?

Answer 4

-the result of cell division from the zygote
-inherits characteristics from both parents

Question 5

Asexual reproduction - advantages

Answer 5

Adv: -can produce lots of offspring very quickly because of the fast reproductive cycle.
-only one parent is needed, meaning organisms can reproduce whenever conditions are favourable

Question 6

Asexual reproduction - disadvantages

Answer 6

-there’s no genetic variation, so if environment changes (unfavourable conditions), the whole population may be affected

Question 7

Sexual reproduction - advantages

Answer 7

-creates genetic variation within the population, which means individuals with different characteristics
-species more adaptable to change in environment
-This can lead to natural selection and evolution

Question 8

sexual reproduction - disadvantages

Answer 8

-takes more time and energy than asexual reproduction, so organisms produce fewer offspring in their lifetime
-organisms need to find and attract mates
-two parents are needed for sexual reproduction, can be a problem if individuals are isolated

Question 9

what are DNA strands?

Answer 9

-polymers made up of lots of repeating units called nucleotides
-each nucleotide consists of a sugar, phosphate group and one ‘base’

Question 10

what does the sugar and phosphate groups do?

Answer 10

-they alternately form a ‘backbone’ to the DNA strands

Question 11

What are the different bases?

Answer 11

One of four different bases joins to each sugar:
A (adenine, T (thymine), C (cytosine) and G (guanine)

A pairs with T
C pairs with G

Question 12

what are chromosomes?

Answer 12

-long, coiled up molecules of DNA
-found in the nucleus of eukaryotic cells

Question 13

What are genes?

Answer 13

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

Question 14

What is a genome?

Answer 14

ALL of an organisms DNA codes for a genome.

Question 15

Transcription stage 1

Answer 15

RNA polymerase bonds onto the non-coded region before the coded gene (RNA polymerase binding site)

Question 16

Transcription stage 2

Answer 16

The RNA polymerase moves along the gene and breaks the hydrogen bonds between the DNA bases
-allows the process of transcription to start

Question 17

Transcription stage 3

Answer 17

-Complementary mRNA nucleotides match up with the DNA bases on the bottom strand of the gene
-except ‘T’ in the pair ‘A-T’ is replaced with ‘U’

Question 18

Transcription stage 4

Answer 18

-At the end of transcription, complementary mRNA strands are made
-these leave the nucleus and goes to the ribosome

Question 19

Transcription stage 5

Answer 19

DNA strands go back to where they were before the transcription

Question 20

Translation stage 1

Answer 20

Amino acids are brought to the ribosome by another RNA molecule called transfer RNA (tRNA)

Question 21

Translation stage 2

Answer 21

The order in which the amino acids are brought to the ribosome matches the order of base triplets (codons) in mRNA

Question 22

Translation stage 3

Answer 22

-Part of tRNA’s structure is called an anticodon - it is complementary to the codon for the amino acid.
-Pairing of codon and anticodon makes sure that amino acids are brought to the ribosome in correct order

Question 23

Translation stage 4

Answer 23

-The amino acids are joined together by the ribosome.
-This makes a polypeptide

Question 24

Translation stage 5

Answer 24

-Process continues until you reach a stop colon
-The amino acid chain then goes to the endoplasmic rectulum and is folded into a protein

Question 25

what is a mutation?

Answer 25

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

Question 26

what happens if mutation occurs in a gene?

Answer 26

-Produces a genetic variant (alleles)
-This may code for a different sequence of amino acids, which may change the shape of the final protein and so its activity

Question 27

what is an example of an allele?

Answer 27

-The activity of an enzyme might increase, decrease or stop altogether
-This could end up changing the phenotype of an organism

Question 28

what happens if mutation occurs in a non-coding region?

Answer 28

-If mutation happens at an RNA polymerase binding site (non-coding), it could affect the ability of RNA polymerase to bind to it.
-It might make it easier or more difficult to bind to
-This will affect how much mRNA is transcribed, affecting how much protein is made

Question 29

what are alleles?

Answer 29

-Different versions of genes
-represented by letters in genetic diagrams
-you have two alleles of every gene in your body, one on each chromosome in a pair

Question 30

what is a homozygous trait?

Answer 30

-when an organism has two alleles for a particular gene that are the same

Question 31

what is a heterozygous trait?

Answer 31

-when an organism has two alleles for a particular gene that are different

Question 32

what are dominant and recessive alleles?

Answer 32

-some alleles dominant (shown with a capital letter)
-some are recessive (shown in a lowercase letter)
-dominant alleles overrule recessive alleles so if one ‘c’ and one ‘C’ are present, then the ‘C’ will determine what characteristic is present