Inheritance Flashcards
Define ‘Gene’
A length of DNA on a chromosome normally coding for a specific
polypeptide.
Define ‘Locus’
A specific position on a chromosome where a gene is located.
Define ‘Dominant’ allele
A dominant allele will always be expressed in the phenotype when present.
(It is represented with a CAPITAL letter).
Define ‘codominant’
Alleles that are equally expressed in a heterozygote.
Define Phenotype
The characteristics of an organism resulting from both its genotype and the
effects of the environment.
Define Genotype
The genetic make-up of an organism i.e. its alleles.
(This is always a pair of letters).
Homozygous
Both alleles for a gene are identical.
Heterozygous
Both alleles for a gene are different
what is monohybrid inheritance?
Monohybrid inheritance is
the inheritance of a single
gene.
Why are Test Crosses Carried Out?
The only genotype that we can be certain of is that of an organism showing a recessive phenotype.
An organism showing the dominant phenotype can either have a homozygous or heterozygous
genotype.
A test cross or back cross is used to determine the genotype of the organisms with the dominant
phenotype.
Why may a dihybrid cross be carried out?
This method is used to determine the genotype of an organism showing two dominant phenotypes.
The organism can either be homozygous or heterozygous
What is codominance?
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Codominance refers to inheritance patterns when both alleles in a heterozygous organism are
equally expressed.
Example of codominance in humans?
Blood groups in humans
Another example of codominance is the
human blood group AB, which is the
result of two alleles A and B, both being
equally expressed in the phenotype,
neither being dominant to the other.
However, blood group O is recessive to
both blood group A and B.
explain linkage
each chromosome carries many different genes and these are inherited together during
meiosis. These genes are therefore link
how is crossing over important in causing variation?
each chromosome carries many different genes and these are inherited together during
meiosis. These genes are therefore link
what are the 3 ways that meiosis results in variety?
- Two haploid gametes (sex cells) must fuse
during fertilisation; as each contains half the genetic information (chromosomes) of the
parent - The random distribution and independent assortment of homologous chromosomes on
the equator of the spindle during metaphase I of meiosis. When the homologous
chromosomes separate, the daughter cells contain different combinations of genetic
information. - Crossing over during chiasmata formation during prophase I of meiosis.
