Genetic Variation Flashcards
Chiasma
The point in which paired chromosomes contact during meosis
OR
The contact point between the two chromatids of a chromosome during meiosis.
OR
a point at which paired chromosomes remain in contact during the first metaphase of meiosis, and at which crossing over and exchange of genetic material occur between the strands.
Crossing over
Two homologous chromosomes pair up, creating a homologous pair of chromosomes. The non-sister chromatids swap alleles. Resulting in new combinations of alleles, meaning there is genetic variation.
Diploid Cell
A cell that contains a complete set of chromosomes (e.g in humans 46 chromosomes)
Haploid Cell
A cell that contains half as many chromosomes as a diploid cell (e.g in humans 23 chromosomes)
Gamete
A reproductive cell having haploid number of chromosomes (e.g in females egg and males sperm)
Independent Assortment
when homologous chromosomes line up in the equator (centre) of the cell, independently of other pairs. Resulting in a randomised line. They are then separated in segreation which resultings in genetic variation as each gamaete receives one chromosomes, meaning there will be different allees in each gamete.
locus
a location a given gene occupies on a chromosome
Meiosis
A type of cell division in sexually reproducing organisms that produces gametes and reduces the number of chromosomes in the reproductive cells from diploid to haploid.
Segregation
The separation of homologous chromosomes. Resulting in each gamete receiving one allele or chromosome
OR
Each gamete / daughter cell receives a single allele / copy of each gene OR results in unique combination of alleles
Mutation
A permanent change to the base sequence of DNA - which may result in a new allele. This causes genetic variation as if the mutation occurs in a gamete it may be passed on to offspring if the gamete is fertilised.
Mutagen
An agent that can create a mutation e.g chemicals, radiation etc
Co-Dominances
An individual who is heterozygous and expresses both phenotypes associated with both alleles and are equally and independently expressed.
Complete Dominance
A relationship between alleles of a single gene, in which one allele masks the phenotypic expression of another allele at the same gene locus.
Incomplete Dominance
Neither allele is dominant and the heterozygotes is intermediate in phenotype between the two homozygotes. A heterozygous individual which phenotype is a combination of both alleles phenotype.
Multiple Alleles
Two or more alleles present in a species for a particular gene
Lethal Allele
Gene mutations result in gene product which is not only functional but also affects the organism’s chances of survival. Lethal alleles are alleles that cause an organism to die when present in a homozygous condition.
Pure breeding
A group of identical individuals that always produce offspring of the same phenotype when intercrossed.
Test Crossing
crossing an unknown genotype individual with a homozygous recessive individual to determine the unknown individual’s genotype. This is done to determine whether the genotype is heterozygous or homozygous dominate
Linked Genes
When two alleles are on the same chromosome and are often inherited together
Genetic Diversity
different genetic combinations in an gene pool
Gene pool
total genetic makeup (alleles) in an interbreeding population
Evolution
the change in characteristics of a population over time
Natural Selection
the name for the process by which beneficial phenotypes in a population tend to survive and reproduce while unfavourable phenotypes tend to be lost
Bottleneck effect
Is where there is a large reduction in a population due to an environmental change (natural disasters) or human actions
Founders effect
Founders effect is when a small group of a population is geographically isolated from the original population or emigrate somewhere else
Gene flow
is the process in which individuals emigrate (leave) out of the population or immigrate (arrive) into the population
Genetic drift
the frequency of alleles change due to chance, rather than selective pressures
Heterozygous
A individual with two different alleles for the same trait
Homozygous Recessive
An organism or cell with two recessive alleles for a single trait
Homozygous Dominnatn
An organism or cell with two dominant alleles for a single trait.
Relationship between gene, alleles DNA and chromosomes
dna.is.genetic.information.A chromosome is a specific strand of DNA, which subdivides into genes. a gene codes for aspecific ascpet/trait, alleles are variations of genes. Genes are built into chromomes which are built into DNA
OR
Alleles are different forms of same gene. Genes are linearly arranged on chromosomes. Chromosomes contain genetic material of cell i.e. DNA. So chemically alleles, genes, chromosomes are all DNA !