What is a gene?
A length of DNA that holds the instructions for a characteristic
Define: gamete
Sex cell of an organism e.g. sperm, egg, pollen or ova
What is a pedigree chart?
A diagram that depicts the biological relationships between an organism and its ancestors
What is genetic diversity?
A measure of the different genetic combinations within a gene pool
Define: natural selection
The process by which heritable traits increase an organism's chances of survival and reproduction.
Define: homozygous
The same form of the allele is present in the genotype e.g. HH, hh
Define: Population bottleneck
An event that drastically reduces the size of a population. It may be caused by various events, such as an environmental disaster.
The type of cell division which produces gametes
Meiosis
Define: Incomplete dominance
Heterozygous individuals have a phenotype that is intermediate between the two homozygous phenotypes
What is the genotype ratio of the punnett square?
3RRTT, 4RRTt, 1RRtt, 3RrTT, 4RrTt, 1Rrtt,
What is F1
The parental generation (P) is the first set of parents crossed. This generation consists of all the offspring from the parents.
Define: allele frequency
A measure of the relative frequency of an allele on a genetic locus in a population.
Describe: segregation
The process that occurs during meiosis where pairs of alleles are separated when the homologous chromosomes split
Define Haploid
When a cell has half the usual number of chromosomes.
Define: co-dominance
Heterozygous individuals have a phenotype that shows the phenotype of both parents
Define: Gene pool
Refers to the total number of alleles of every individual in a population.
What is migration?
Movement of organisms into (immigration) and out (emigration) of a population.
What is a test cross?
A genetic cross between a homozygous recessive individual and a corresponding suspected heterozygote to determine the genotype of the latter.
What is the genotype?
The genetic make-up of the organism
What is crossing over?
During meiosis, when the homologous chromosomes line up at the equator, they can exchange genetic information.
What is a Chiasma?
The point of contact, the physical link, between two (non-sister) chromatids belonging to homologous chromosomes during crossing over
Fertilisation
The union of male (sperm) and female (ovum) gametes to produce a diploid zygote in reproduction
Define evolution
Is the change in the characteristics of a species over time and relies on natural selection.
What is Asexual reproduction?
Reproduction involving only one parent. Doesn’t produce genetic variation.
Define: Genetic drift
The change in frequency of an existing gene variant (allele) in a population due to random chance alone and not natural selection.
Define: complete dominance
The dominant allele in a heterozygous individual completely masks the effect of the allele that is recessive
What is sexual reproduction?
Reproduction involving two parents. Produces genetic variation.
Define: diploid
A cell or an organism consisting of two sets of chromosomes: usually, one set from the mother and another set from the father.
What does multiple alleles mean?
When three or more alternative forms of a gene (alleles) can occupy the same locus. e.g. ABO blood types
Define: heterozygous
Different forms of the allele are present in the genotype e.g. Hh
Define: Mutation
A permanent change in the bases on DNA. It is the only way of creating new alleles
Define: Allele
Different forms of a gene due to slightly different order of bases e.g. brown eyes and blue eyes
Describe: founder effect
The loss of genetic variation when a new population is established by a very small number of individuals from a larger population.
What are homologous chromosomes?
Chromosome pairs (one from each parent) that are similar in length, gene position, and centromere location.
What is a somatic cell?
Body cells. If a mutation occurs in these cells, it will not be passed on to offspring.
What is: Alleles that produce a gene product that kills the offspring
Lethal genes
What is independent assortment?
The way the homologous chromosomes line up at the equator maternal and paternal, is completely random
Define: pure breeding
A group of identical individuals that only produce one type of gamete due to the fact they are homozygous
Linked genes are...
Genes located on the same chromosome that tend to be inherited together
Define: phenotype
The physical appearance of the organism
Define: selection pressure
Environmental factors that influence the survival and reproductive success of individuals within a population.