Transcript Keywords - NCEA Level 2 Biology

Keywords
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Independent assortment: Alleles of genes on nonhomologous chromosomes assort independently
during gamete formation.
Segregation: The two alleles for each gene (on
homologous chromosomes) separate during
gamete formation.
Linkage: Genes which are carried on the same
chromosomes tend to be inherited together.
Crossing over may separate linked genes.
Chromosome map: Shows the genes on one
chromosome and how close together they are.
Which is the odd one out and why?
Independent Assortment
Chromatid
Crossing Over
Chromosome mutation
6. Linked genes
and gene
maps
SC: Explain how linkage may
affect phenotypes shown in
offspring
Describe what is shown by a
gene map.
Mutations
pg 93
Benefici
al /
Harmful
Where,
when ,
how?
Sources of
variation
Reproduction
Population
Genetics pg 123
Pg 109
Using
monohybrid
crosses
Lethal
alleles
pg 110
Linkage
pg 103
Genetic
Variation and
Change
Mendelian
Genetics
Incomplete
dominance
pg 109
Sexual
Gene Pools
pg 92
Genetics
Tool Box –
Intro.
Changes to allele
frequencies
Using dihybrid
crosses pg 113
Codominan
ce pg
109
Multiple
alleles pg
110
Segrega
-tion pg
99
Independ
ent
assortment
pg 101
Crossing
over pg
102
Linkage
pg 118
Independent
assortmen
t pg 114
Genetic
Drift pg
126
Migratio
n pg
126
Natural
selectio
n pg
132
Independant assortment
recap
In Labradors black(B) is dominant to brown
coat(b) and blindness (n) is recessive to normal
vision (N).
As these two genes are on different
chromosomes they move independently into
gametes depending on how they line up along
the equator.
If two dogs were bred which were heterozygous
for each trait what possible gametes could
form?
What percentage of each gamete should form?
Did you know?
 The
number of genetic variations possible
in our sperm and eggs thanks to
independent assortment is 223 or 8388608
– that is before we add in variation due to
crossing over or mutation.
Linked genes
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Are genes which are on the same chromosome.
They do not show independent assortment unlike
genes on different chromosomes.
During Anaphase two, these genes travel to the
same gamete together.
Linked genes have different phenotype ratios in
gametes than genes on different chromosomes.
Linked genes only become separated if crossing
over occurs between the two gene locii.
Gene Maps
 Tell
us three things…
1. What genes are linked
2. What genes are on the chromosome
3. How close genes are to each other and
the likelihood of them being separated
by crossing over.
See the sample human gene map.
Sex Linkage
A sex linked condition on the Y chromosome will
not show in females. XY’
X linked recessive traits show up more in males
as they only have one X chromosome so if they
gain that allele from their mother, they will have
that trait. X’Y
For a female to show an X linked trait they must
have two copies of the allele. X’X’
Examples of sex linked traits: haemophilia, red
green colour blindness, muscular dystrophy
Example Exam Question
Discuss how and why the different processes
that can occur during meiosis can lead to
genetic variation between individuals.
Take into account the following:
• independent assortment
• segregation
• recombination / crossing over.