KA4- Variation and Inheritance Flashcards
Variation
Different characteristics
Combining genes from 2parents within a species of sexually reproducing organisms contributes to this
Types: discrete and continuous
Examples: eye colour, eight, weight
Discrete variation
Characteristics controlled by a single gene
One copy inherited from each parent
Can’t be measured
From distinct groups
Examples: blood group, tongue rolling, writing hand, petal colour, seed shape
Continuous variation
Characteristics controlled by more than one gene
Described as polygenic inheritance
Can be measured
Varies from one extreme to another
Examples: height category, body mass, root length of plants, handspan
Polygenic characteristics
Phenotypes that can show a wide range of values
Gene
A location on a chromosome where there is a DNA base sequence that codes for a protein that controls a particular characteristic
Phenotype
The physical appearance of an organism because of its gene
Genotype
Complete set of genes possessed by an organism
Statement of the alleles it has for a characteristic
Alleles
Different versions of a particular gene
Different version of a gene contain different DNA base sequences that code for different proteins and produce different phenotypes
Example: allele R produces round shape seeds and allele r produces wrinkled shape seeds
Homozygous
2 identical alleles of a gene
Examples: BB, bb, ZZ
Heterozygous
2 different alleles of a gene
Examples: Bb, Zz, Aa,
Dominant allele
Capital letter
Masks recessive allele
Organism only needs one copy for it to be shown
Examples: Z, T
Recessive allele
Lowercase letter
Masked by dominant allele
Organisms always ends two copies before it is shown
Examples: zz, aa, tt
Monohybrid cross
Genetic cross that shows the inheritance of characteristics
Punnets square
A grid that shows the possible combination of alleles that can result at fertilisation
Determines the possible phenotypes and genotypes
Rough example:
R r
RR Rr
Rr rr
