CIE A Level: Inheritance

sexual reproduction

production of genetically unique offspring involving the fusion of gametes to produce a zygote

gamete

haploid sex cells which fuse together to form zygotes

fertilisation

the fusing of two gamete's haploid nuclei to form a diploid zygote

diploid

containing two complete sets of chromosomes (2n)

haploid

containing one complete set of chromosomes (n)

homologous pair of chromosomes

two chromosomes that carry the same genes (though they might be different alleles of that gene) in the same loci

meiosis

nuclear division that results in the production of four haploid daughter cells that are gametes

bivalent

two homologous chromosomes positioned next to each other during meiosis I

chiasma (plural: chiasmata)

a position on a chromosome at which two non-sister chromatids (i.e. chromatids on different chromosomes) cross over each other and can exchange genetic material

crossing over

the exchange of alleles between two non-sister chromatids within a homologous pair of chromosomes. This occurs during meiosis I

reduction division

nuclear division that results in there being fewer chromosomes in each cell. The first division of meiosis is an example of this

locus (plural: loci)

the position of a gene on a chromosome

alleles

different versions of a gene

independent assortment

the production of different combinations of alleles in daughter cells due to the random alignment of bivalents during metaphase I of meiosis

genotype

all of the alleles possessed by an organism

homozygous

having two identical alleles for a particular gene

heterozygous

having two different alleles for a particular gene

phenotype

the observable characteristics of an organism resulting from the expression of its genotype and environmental factors

dominant

the allele that affects the phenotype whether or not another allele is present

recessive

the allele that only affects the phenotype if no dominant allele is present

multiple alleles

when a gene has three or more different alleles, e.g. the gene that determines A, B, AB, or O blood types

codominant

when different alleles both affect the phenotype simultaneously

monohybrid inheritance

the study of how the alleles of just one gene are passed from parents to offspring