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BIOLOGY REVISION
WHAT DOES THE STANDARD SAY?
Bi o l o gi cal i d e a s re l a t i n g to ge n et i c v a ri a ti on a re l i mite d to c o n c e pt s a n d
pro ce s ses co n n ecte d w i th :
 t h e c o n t i nuit y o f l i fe ba s e d o n t h e i n h erit able n a t ure o f D N A
 l i n ks bet we e n D N A a n d va ri at ion i n ph e n ot y pes
 va ri at ion i n ph e n ot y pes a s a da pt i ve fe a t ure s .
B i o logic al c o n c e pt s a n d pro c e s ses re l a t ing to t h e i n h erit able n a t ure o f D N A w i l l
be s e l ec ted fro m :
 t h e ro l e s o f D N A i n bot h c a rr y i n g i n s t ruc t ions to t h e n ex t g e n e rat ion a n d
dete rm i ning ph e n ot y pe
 t h e re l a t ionship bet we e n D N A , a l leles, g e n e s, a n d c h ro m osomes
 t h e way i n w h i c h g e n ot y p e dete rm i nes ph e n ot y pe
 t h e way c h ro m osomes ex i s t a s pa i r s s o t h a t i n dividuals i n h erit t wo c o pi e s o f
e a c h g e n e.
B i o l og i c al c o n c e p t s a n d p r o c e s s e s r e l a t i n g to v a r i a t i o n i n p h e n o t y p e w i l l b e s e l e c te d
from:
 t h e s i g ni fi c a n c e o f a n a l l e l e a s a n a l te r n a t i v e v e r s i o n o f a g e n e
 t h e r o l e o f m u t a t i o n s i n f o r m i n g n ew a l l e l e s
 t h e r o l e o f m e i o s i s i n g e n e r a t i n g g a m ete s ( s t u d e n t s a r e n o t r e q u i r e d to p r o v i d e t h e
names of the stages of meiosis)
 t h e s i g ni fi c a n c e o f s ex u al r e p r o d uc t i o n ( i n p r o d uc in g a n ew m i x o f a l l e l e s )
 t h e p a t te r n s o f i n h e r i t a n c e i nv o l v i n g s i m p l e m o n o hy b r i d i n h e r i t a n c e s h o w i n g
c o m p l ete d o m i n a n c e , s ex d ete r m in a t i o n , p o s s i b l e g e n o t y p e s , a n d p h e n o t y p e r a t i o s .
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B i o l og i c al c o n c e p t s a n d p r o c e s s e s r e l a t i n g to v a r i a t i o n i n p h e n o t y p e s a s a d a p t i v e
f e a t u r e s w i l l b e s e l e c te d f r o m :
 i n h e r i t a b l e a n d n o n - i n h e r i t a b l e v a r i a t io n s t h a t ex i s t w i t hi n a g r o up o f l i v i n g
organisms
 d i f fe r i n g r a te s o f s u r v i va l b y v a r i o us m e m b e r s o f a g r o up m ay d e p e n d o n t h e i r
phenotype
 t h e i m p o r t a n c e o f v a r i a t i o n w i t hi n p o p ul a t io n s ( p o p ul a t i o n a n d s p e c i e s s u r v i va l ) i n
a c h a n g i n g e nv i r o n m e n t s u c h a s p e s t i n f e s t a t i o n , d i s e a s e , d r o ug h t , o r f l o o d
 t h e a d v a n t a g e s a n d d i s a d va n t a g e s o f s ex u a l r e p r o d uct i o n .
KEY DEFINITIONS
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Gene
allele
mutation
genotype
phenotype
gamete
zygote
dominant
recessive
homozygous
heterozygous
pure breeding
somatic mutation
gamete mutation
WHAT NCEA MARKERS WANT TO SEE
 Allele- alternative form of the same gene
 Gene- a section of DNA (or chromosome) that codes for a
particular characteristic/protein
 Phenotype- the physical appearance of a trait/genotype
 Genotype- the genetic make up of a trait made up of a
combination of alleles
 Mutation- A permanent mistake in a section of DNA within
an organism
 Dominant- An allele where only one copy is required for it
to be expressed over the recessive allele
 Recessive- An allele where two copies are required for the
characteristic to be expressed
CONTINUED
 Homozygous- a genotype that will contain two of the same
alleles for the gene.
 Heterozygous- a genotype that will contain two different alleles
for the same gene
 Pure Breeding- An organism that will be either homozygous
dominant or recessive for a particular trait
 Somatic mutation- a mutation that cannot be inherited because
these cells only reproduce via mitosis
 Gamete mutation- a mutation that can be inherited because
these cells will produce via meiosis
 Gamete- sex cells (sperm, egg, pollen) that can transfer genetic
information from parents to offspring. Will contain half a set of
chromosomes
 Zygote- a fertilised egg (via sperm or pollen) that well develop
into an embryo. Will contain a full set of chromosomes
MAIN IDEAS FOR NCEA QUESTIONS
 (a) Explain how the pedigree chart can be used to show that
albinism is a recessive trait.
 In your answer you should:
 • define the terms dominant and recessive
 • state the genotypes of albino and normal gorillas
 • complete a labelled Punnett square to support your answer
 • explain how your Punnett square shows that albinism is a
recessive trait.
 Note: Refer to the pedigree char t opposite.
 QUESTION THREE: A GIRL OR A BOY?
 A couple are expecting their third child. They already have one
boy and one girl.
 (a) Discuss the likelihood of their third child being a girl.
 In your answer you should:
 • explain how sex is determined in humans
 • complete a Punnett square showing sex inheritance
 • explain the relevance of the couple already having children.
 One of the parents is a teacher who developed deafness last
year as a result of having noisy classes.
 Discuss the likelihood of this type of deafness being inherited
by the new baby.
 In your answer you should consider:
 • the reason for the parent’s deafness
 • what types of characteristics are inherited
 • the ef fects of genetics and the environment on deafness in
of fspring.
 QUESTION FOUR: VARIATION
 Genetic variation is important in a population.
 (a) Describe what is meant by the term genetic variation, and
explain its importance to a population.