topic 3 - genetics

Question 1

what are the advantages of sexual reproduction?

Answer 1

-produce variation (due to genetic variation)
-survival advantage by natural selection
-> sped up by humans in selective breeding

Question 2

what are the disadvantages of sexual reproduction?

Answer 2

-lots of time and energy needed to find a mate
-not possible for isolated individual to reproduce

Question 3

what are the advantages of asexual reproduction?

Answer 3

-only 1 parent needed -> more energy and time efficient (no wasted gametes)
-more reliable offspring
-identical offspring - can be produced in favourable conditions

Question 4

what are the disadvantages of asexual reproduction?

Answer 4

-doesn’t lead to genetic variation in population
-species may only be suited to 1 habitat
-disease may affect all individuals

Question 5

what are gametes?

Answer 5

sex cells (sperm and egg)

Question 6

what is a zygote?

Answer 6

fertilized egg

Question 7

what are the stages of mitosis?

Answer 7

IPMATC

Question 8

what is DNA organised into in the nucleus?

Answer 8

chromosomes

Question 9

how many chromosomes do normal body cells have?

Answer 9

46 - diploid

Question 10

how many chromosomes do gametes have?

Answer 10

23 - haploid

Question 11

what is meiosis?

Answer 11

type of cell division that results in 2 daughter cells - each with half the number of chromosomes of the parent cells (production of gametes)

Question 12

describe meiosis?

Answer 12

-DNA duplicates
-divides into 2 cells - each have 1 full set of DNA
-cross over occurs - mixes DNA of mother and father
-second division occurs - leaves 4 genetically different daughter cells each with half set of DNA - making them haploid (1n)

Question 13

how many chromatids are in 2 replicated chromosomes after meiosis?

Answer 13

4 sister chromatids

Question 14

what is meiosis’ role in sexual reproduction and growth of the embryo?

Answer 14

-meiosis needed to form gametes
-these fuse to from zygote
-zygote divides by mitosis to form embryo

Question 15

what is the genome?

Answer 15

entire genetic material of an organism

Question 16

what is a gene?

Answer 16

short section of DNA that instructs for a particular protein

Question 17

what is DNA?

Answer 17

deoxyribonucleic acid - polymer of nucleotides made up of 2 strands that form a double helix

Question 18

what are the bases of DNA?

Answer 18

C, G, A, T

Question 19

what are the pairs of bases?

Answer 19

C with G and A with T

Question 20

what is the structure of DNA?

Answer 20

-polymer - joined by nucleotides - sugar phosphate backbone
-2 strands coil to form a double helix
-linked by series of complementary bases joined by weak hydrogen bonds

Question 21

what is the hydrogen bonding rule for the base pairs?

Answer 21

C bonds to G with 3 hydrogen bonds
A bonds to T with 2 hydrogen bonds

Question 22

how can DNA be extracted from fruit cells?

Answer 22

1. mash strawberries in beaker containing detergent and salt
2. detergent breaks down cell membranes releasing DNA - salt clumps DNA together
3. filter mixture to get froth and big insoluble bits of cell out
4. add ice-cold ethanol slowly stop when as much has been added as there is filtrate
5. DNA insoluble in cold ethanol so will appear as a stringy white precipitate

Question 23

what does the DNA base sequence code for?

Answer 23

sequence of amino acids in the polypeptide chain of a protein which fold to produce specifically shaped proteins (e.g. enzymes)

Question 24

where does protein synthesis occur?

Answer 24

ribosomes but DNA is too large to leave nucleus so has to go through transcription

Question 25

what is transcription?

Answer 25

where bases in DNA is used to make small, single strand of mRNA

Question 26

what bases does RNA use?

Answer 26

C, G, A, U - instead of T

Question 27

describe transcription

Answer 27

1. section of DNA (gene) unwinds and unzips (hydrogen bonds between 2 stands breaks)
2. RNA nucleotides bind to exposed bases on template strand - RNA polymerase joins
3. forms mRNA - complementary to template strand + matches coding strand (but RNA)
4. mRNA leaves nucleus to go to ribosomes
5. 2 strands of DNA join back up

Question 28

describe translation

Answer 28

1. first mRNA codon is read and a tRNA molecule with complementary anticodon binds bringing the first amino acid
2. next codon read and tRNA with complementary anti-codon binds with 2nd amino acid - peptide bond forms between amino acids
3. only 2 tRNA’s can attach at a time so first one leaves and is free to collect another amino acid
4. chain grows as process continues and ribosome moves down mRNA
5. polypeptide formed