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Section H: Human Inheritance (Terms (using hair colour as an example)…
Section H: Human Inheritance
Terms
(using hair colour as an example)
Genes
exist in alternative forms called
Alleles
The ginger hair allele is
recessive
because it can be hidden by a brown hair allele. therefore somebody to have ginger hair, they must have two copies of the ginger hair allele.
e.g. the gene is for hair colour two alleles; one for brown one for ginger.
The brown hair allele is
dominant
because it determines the characteristics even if only one copy is present.
When a
gamete
made, it will only contain one of the alleles
the
Phenotype
is the appearance / measurable characteristics (e.g. hair colour)
Homozygous
is when both the alleles are the same
Genotype
: The alleles each cell has for a certain feature
Heterozygous
is when the two alleles are different
genes
body is made up of cells. each cell contains a
nucleus
which controls the cell
Each nucleus contains lots of thin threads called
chromosomes
Chromosomes
carry information which controls how your body works and what you look like
Each chromosome is made up of tangled threads. each thread is made up of a very long molecule called
DNA
A
gene
is a length of DNA.
each gene gives instructions for a different characteristic e.g. eye colour
Genetic diagrams
A cross between two parents who possess different forms (alleles) of a gene is called monohybrid inheritance.
family pedigrees
numbers of chromosomes
46 is the diploid number chromosomes in a human cell
23 is the haploid number of chromosomes in a human
Structure of DNA
a DNA molecule
two strands
coiled together in the shape of a
double helix
(two spirals)
The two strands are held together by chemicals called
bases
. There are
four
different bases:
ADENINE (A)
,
CYTOSINE (C)
,
GUANINE (G)
and
THYMINE(T)
The bases are
paired
and they always pair up in the same way - its always A-T and C-G. this is called
complementary base-pairing.
DNA is a type of
nitric acid
.
sex determination
the sex of a person is determined by one pair of Chromosomes - XX for female and XY for males
