Key words Flashcards
(31 cards)
PREFORMATION
The belief that an embryo is a miniature adult (homunculus). There is no distinction between different stages of life
EPIGENESIS
The belief that adult forms arise by development from different forms. The embryo contains information specifying a developmental programme
MENDEL’S 1ST LAW
Segregation - there are two copies of each ‘particle’, one from each parent. They remain unaltered and one is passed on at random in each sperm/egg
MENDEL’S 2ND LAW
Independent assortment - traits are inherited independently
MENDEL’S 3RD LAW
Dominance - the inherited ‘particles’ may be either a) dominant or b) recessive
ALLELE
A variant form of a given gene, meaning it is one of two or more versions of a known mutation at the same place on a chromosome
HOMOZYGOUS
An individual carrying two identical alleles
HETEROZYGOUS
An individual carrying two different alleles
GENOTYPE
The specific allele composition of an individual
PHENOTYPE
The observable properties of an individual
MITOSIS
A type of cell division that results in two diploid daughter cells each having the same number of chromosomes as the parent nucleus, typical of ordinary tissue growth
MEIOSIS
A type of cell division that results in four haploid daughter cells each with half the number of chromosomes of the parent cell, as in the production of gametes and plant spores
PLEIOTROPY
When one gene influences two or more seemingly unrelated phenotypic traits
POLYGENIC INHERITANCE
Occurs when one characteristic is controlled by two or more genes. Often the genes are large in quantity but small in effect. Examples of human polygenic inheritance are height, skin color, eye color and weight
COMPLEMENTATION TEST
A test to establish the relationship between 2 recessive mutations by checking the phenotype of the offspring. If the parental mutations are at the same loci, the progeny are affected
ADDITIVE EFFECTS OF POLYGENIC INHERITANCE
Each allele of each gene has an additive effect e.g. each contributing allele produces one unit of colour
EPISTASIS
The effect of a gene mutation is dependent on the presence or absence of mutations in one or more other genes
RECESSIVE EPISTASIS
Two alleles have to be inherited in order for the phenotype of the second gene to be masked e.g. dog coat colours
DOMINANT EPISTASIS
One allele of a gene has to be inherited to mask the alleles of another gene e.g. squash colouration
CODOMINANCE
Neither allele can mask the expression of the other allele e.g. blood groups
INCOMPLETE DOMINANCE
When a dominant allele, or form of a gene, does not completely mask the effects of a recessive allele, and the organism’s resulting physical appearance shows a blending of both alleles e.g. snapdragons
UNDERDOMINANCE
The selection against the heterozygote, causing disruptive selection and divergent genotypes. It exists in situations where the heterozygotic genotype is inferior in fitness to either the dominant or recessive homozygotic genotype
OVERDOMINANCE
Where the phenotype of the heterozygote lies outside the phenotypical range of both homozygous parents / heterozygous individuals have a higher fitness than homozygous individuals e.g. Sickle cell anaemia
VARIABLE EXPRESSIVITY
The degree in which a genotype is phenotypically expressed. For example, multiple people with the same disease can have the same genotype but one may express more severe symptoms, while another carrier may appear normal e.g. Tuberolis Schlerosis
