sb3 genetics (paper 1) Flashcards
define gene
a section of DNA that codes for a single characteristic, e.g hair and eye colour
what does DNA stand for
deoxyribonucleic acid
define allele
a variation of the same genetic
what are the two types of variation
environmental and genetic
what is genetic variation (give examples)
characteristics inherited by your parents (blood type, eye colour, hair texture and colour)
what is environmental variation (give examples)
characteristics you get from the environment around you (scars, hair length, piercings)
give characteristics that could be both genetic and environmental
height, hair colour, skin colour
what is a zygote
formed at fertilisation when a sperm and egg fuse
how many chromosones does a zygote have
46
how many pairs of chromosones does a zygote have
23
how many chromosones does a sperm cell have
23
how many chromosones does an egg cell have
23
what is a recessive allele
a type of allele that needs two genes to express itself
what is a dominant allele
a type of allele that only needs one gene to express itself
what is homozygous
when the genotype letters are the same
what is heterozygous
when the genotype letters are different
state what is meant by the term genome
all of the DNA within the nucleus
state what is meant by the term genotype
a letter to show the genetic code / allele
state what is meant by the term phenotype
the physical characteristics of an organism
describe the dna structure
- in a double helix
- sugar phosphate backbone
- made of complementary genetic bases
name the four bases
- adenine (a)
- guanine (g)
- thymine (t)
- cytogine (c)
in the dna structure, what is complementary to the base adenine?
thymine
in the dna structure, what is complementary to the base guanine?
cytogine
in the dna structure, what is complementary to the base thymine?
adenine
in the dna structure, what is complementary to the base cytogine?
guanine
what is a mutation
a random change in the genetic base
draw the detailed DNA structure
what is the purpose of mitosis
for growth and repair
what is a gamete
a sex cell
give examples of gametes
sperm, egg, pollen
define haploid cells
cells with half the chromosones (23)
define diploid cells
cells that have 46 chromosones
what happens in asexual reproduction
- uses mitosis
- no fusion of gametes
- no mixing of genetic information
- genetically identical
- one parent
what happens in sexual reproduction
- uses meiosis
- mixing of genetic information
- leads to a variety of offspring
- two parents
describe the stages of extracting DNA from fruit and the purpose of each step
- mash the fruit with salt water to seperate cells
- sieve the mixture to get the fruit soup
- add detergent to rupture the cell membrane
- add protease enzyme to uncoil the DNA
- slowly add ice cold ethanol to slow enzyme activity and make it insoluble (there will be a transparent layer ontop)
- use a wooden stick/wire to extract the DNA
advantages of sexual reproduction
- lots of variation
- increases species survival due to the mixture of chromosones
advantages of asexual reproduction
- very fast
- doesn’t require finding a mate
- uses less energy
disadvantages of sexual reproduction
- takes extremely long
disadvantages of asexual reproduction
- doesn’t have many variations
what are the stages of meiosis
- prophase 1
- metaphase 1
- anaphase 1
- telophase 1
- prophase 2
- metaphase 2
- anaphase 2
- telophase 2
(meiosis) what happens in prophase 1
- chromosones are condensed
- they cross in same size and shape pairs to transfer genetic info
(meiosis) what happens in metaphase 1
- chromosones are lined up in the middle
(meiosis) what happens in anaphase 1
- spindle fibres pull apart the chromosones
(meiosis) what happens in telophase 1
- cell is split into two
(meiosis) what happens in prophase 2
- spindles and chromosones are formed in the two daughter cells formed from telophase 1
(meiosis) what happens in metaphase 2
- chromosones are lined up in the middle
(meiosis) what happens in anaphase 2
- chromosones are pulled away
(meiosis) what happens in telophase 2
- cell is split into two (results in 4 daughter cells total)
what is the purpose of protein synthesis
to make protein
what are the two main processes in protein synthesis
transcription and translation
what happens in transcription
- section of dna containing the gene to be transcripted unwinds
- dna strands seperate
- rna polymerase binds to non coding dna located infront of the gene
- rna polymerase produces a complementary mrna strand from the coding dna of the gene (a and u, and c and g)
- mrna leaves the nucleus
- attatches to a ribosome
- codons in the mrna code for specific amino acids
what happens in translation
- transfer of amino acids to the ribosome by trna
- anticodons on trna (match codons on mrna strands)
- amino acids are linked to form polypeptides by peptide bonds
- the order of bases in a section of dna decides the order of amino acids in the protein
what blood type is recessive
o
what four blood types are common in the abo system?
- type A, in which only the A antigen is present.
- type B, in which only the B antigen is present.
- type AB, in which both the A and B antigens are present.
- type O, in which neither the A nor the B antigen is present.
