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Biology
Inheritance
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Sexual reproduction
Involving 2 parents and fusion of
gametes
and mixing of
chromosomes.
The offspring contains a mixture of
genes
and is
genetically different
to either parents.
Occurs by
meiosis
Fertilisation
The
fusion of the nucleus of a male gamete with the nucleus of a female gamete.
When the gametes combine, they merge the two sets to form 46 chromosomes. Referred as a
diploid.
Gametes are made by
meiosis
Asexual reproduction
Involves
one parent
and there is no fusion of
gametes.
Because there is no mixing of genetic
information.
The offspring is genetically
identical
to the parent.
Occurs by
mitosis
The
genome
Is the entire set of
genetic
material of an organism.
Genes
A small section of
DNA
on a chromosome that codes for a particular sequence of
DNA.
Chromosomes
Two
long strands of
DNA
coiled up to form a
chromosome.
Human body cells contain
23
pairs of chromosomes.
DNA
A
double helix polymer
, made up of
two
strands forming a
twisted ladder
shape.
Gene identification
Identifying
genes
linked to different
disorders.
Mutations
A
mutation
is a permanent change in the
nucleotide
of DNA.
Alleles
Different forms of a particular
gene.
Peoples
characteristics
are determined by the
alleles.
They are either
dominant
or
recessive.
Dominant
Allele
Is
always
expressed, regardless of the other allele.
It only needs
one copy
to be present.
Recessive
allele
Only expressed if the other allele is also
recessive.
Represented by a
lower
case letter e.g bb
Needs
two
copies for it to be present
Polydactyly
Is a
disorder
involving
extra
fingers or toes.
Caused by a
dominant
allele.
Recessive allele
Is caused by a
recessive
allele.
Is a disorder of the cell membrane, it causes
mucus
to build up in the
lungs
and digestive system.
Heterozygous
If the two alleles of a particular gene are
different.
Homozygous
If the two alleles of a particular
gene
are
identical.
Embryonic
screening
Is a form of
genome
screening.
Looking for
genes
that may make that person susceptible to
genetic
disorders.
Advantages of screening
Screening ensures the
implanted
embryos are
healthy.
Prevent
suffering
Financial
saving,
reduction
in disorders that need to be treated.
Disadvantages of screening
Expensive
Ethics
, the embryos that are of no use are
destroyed
which is considered as unethical and against religious views.
Parents become
selective
A
gamete
Reproductive
cells e.g sperm cell
Haploid
(23 chromosomes)
Meiosis
2
Cell divisions
Before the cell divides, the genetic information is duplicated, forming
two
armed
chromosomes.
After
replication
, the chromosomes arrange into
pairs.
First division involved chromosomes lining up the
centre
of the cell.
The pairs are
pulled apart
so each new cell only have
1
copy of each chromosome.
Second
division
involves when the chromosomes line up again and cell
divides.
Forming
4 gametes
which are genetically different as the chromosomes get
shuffled up.
Genotype
The combination of
alleles
that a person as for a particular
trait.
Phenotype
The
observable
characteristics of an organism.
For example,
eye colour
Sex determination
The human body cells has
23
pairs of chromosomes
22
pairs of chromosomes control characteristics only, but
one
of the pairs carry the genes that determines the
sex.