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Inheritance Patterns - Coggle Diagram
Inheritance Patterns
Sex-Linkage
occurs when some genes carried on the X and Y chromosomes code for characteristics
apart from the gender of the individual
when the gene occurs on the X chromosome
females will have two alleles
when the gene occurs on the Y chromosome
males will have one allele
only has one X chromosomes
recessive disorders appear more frequently in males
example
genes for red-green colour vision are carried in the X chromosome
mutant may result in a person being red-green colour blind
Haemophilia is an X-linked disorder
alleles occur on X chromosome
male who inherits one copy of the mutant allele will suffer from the condition
as male has no equivalent allele on the Y chromosome to mask this defective allele
female inherits a mutant allele on one X chromosome
she will not suffer from the disorder if another allele is dominant
known as a carrier
although defective allele may be passed to her sons or daughters
depends on allele inherited from father
females have two X chromosomes
one from each parent
H = normal blood clotting
h = haemophilia
Co-dominance
both alleles are expresses
creates a new phenotype
both behave as dominant alleles
example
pure-breeding cattle may have a red or white coat colour
homozygous
hybrid individuals which have one allele for red and one for white coat colour
heterozygous
special genetic notation is used to represent codominance
letter is chosen to represent the gene
both written as capital letters
as both alleles are expressed
alleles are written as superscripts next to the gene
Incomplete Dominance
there is a blending of the features of the two alleles expressed
giving a hybrid that is intermediate
example
red snap dragon flowers crossed with white snapdragon flowers given pink flowers
incomplete dominant pink hybrids are also seen in tuplids, carnations and roses
Multiple Alleles
three or more alleles for a single gene trait
example
human blood has three alleles
A, B, and O blood type
alleles A and B are co-dominant
as each produce a molecular marker on red blood cells
alleles 'i' are recessive to A and B
no molecular marker in red blood cells
four possible blood groups include: A, B, AB, O
notation
gene is denoted and alleles are represented through superscripts
Autosomal
autosomes are any chromosome that is not a sex chromosome
Autosomal recessive inheritance
version of each characteristic.trait is inherited from both parents
alleles
passed on according to set ratios
either be the same or differ
same = homozygous
differ - heterozygous
in heterozygous individuals the trait expressed is known as the dominant allele
the trait masked is known as the recessive allele
for a recessive gene to be expressed - both alleles need to be recessive
Mendel's first law - dominance
during gamete formation each alleles for a trait segregate
each gamete receives only one allele
Mendel's first law - segregation
the inheritance of more than one trait/gene
the pair of traits separate independently of the other pairs of alleles
Mendel's second law = independent assortment
