Download GENETICS DEFINITIONS

GENETICS
Definitions
Underlined are credit only
Word
Definition
Species
Group of interbreeding organisms whose
offspring are fertile
Differences that occur within a species
Variation
Continuous
Discontinuous
Differences in species showing a range of
values between two extremes e.g. human
height or stem length of plants
Differences in species which show
distinct groups e.g. blood group, flower
colour
Determined by genetic information
Inherited
characteristic inherited from both parents e.g. fur colour
or shape of seeds
Word
Definition
Uniform
Describes the phenotypes of offspring in a
true breeding cross e.g. Roller (RR) x non
roller (rr) = Rollers (Rr)
Cross between true breeding parents with
different phenotypes of the same
characteristic e.g.
Black (BB) x brown (bb)
Symbol for parental generation
Monohybrid
crosses
P
F1
F2
Symbol for first offspring
3:1 (¾ : ¼ )
Ratio of phenotypes in F2
Why ratios
don’t work
Fertilisation is a random process
Symbol for second offspring
Word
Definition
phenotype
the appearance of an individual e.g. red hair
dominant
phenotype or gene which always shows e.g.
tall (TT) x dwarf (tt) = tall (Tt)
recessive
phenotype or gene that can be hidden e.g.
grey (GG) x white (gg) = grey (Gg)
true breeding produces only one type of gametes e.g. GG,
gg,TT,tt.
Gamete
Double
Single
A sex cell which carries one of the two forms
of a gene
the number of sets of chromosomes in a
body cell
the number of sets of chromosomes in a
gamete (sex cell)
Word
Definition
Gamete
formation
Fertilisation
When the reduction of the number of
chromosomes occurs
when chromosome numbers double –
sperm and egg fuse
Gene
Part of a chromosome – two forms of a
gene control an inherited
characteristic
genotype
the genes an organism contains (genetic
make up) e.g. Rr, TT, gg, Ff, Hh
Parent
this individual contributes one of the two
forms of a gene to their offspring
alleles
The name for the two forms of a gene
Word
Definition
X and Y
chromosomes that determine sex
XY
male
XX
female
X or Y
Can be found in male gamete (sperm)
X
Always found in female gamete (egg)
Word
Definition
Selective breeding When humans choose
organisms to breed
Selective breeding Increased yield / increased
examples
growth
Mutation
Change in a chromosome e.g.
Down’s syndrome ( 47)
Mutation rate
radiation
increased by
Advantage of a
Crop plants with extra
mutation
chromosomes
Amniocentesis
Used to detect chromosome
characteristics before birth
Quiz
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Variation –
differences in species
Species –
interbreeding organisms, can produce
fertile offspring
Fertile offspringcan breed
Sterile offspring
can not breed
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Discontinuous variation –
shows distinct (clear cut) groups
Example –
blood group, sex, tongue rolling
Continuous variation –
shows a range of values from one
extreme to another
Example
shoe size, height, pulse rate, weight
• Number of sets of chromosomes in a body
cell
two ( double)
• Number of sets in a sex cell
One ( single)
• When chromosome numbers are reduced
gamete formation
• When chromosome numbers are doubled
fertilisation
• Gamete
sex cell
• Inherited characteristic determined by genetic information
inherited from both parents
• Example –
sex, tongue rolling , blood group
• Phenotype –
appearance of an inherited characteristic
• Example
male/female, roller/non roller, A,B,O,AB
• Dominant phenotype –
always shows
• Example
black X white
black
• Recessive phenotype
can be hidden
• genotype–
all the genes of an organism
• gene
part of a chromosome
• alleles
two forms of a gene e.g. T or t