Genetic Variation Flashcards Preview

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Flashcards in Genetic Variation Deck (27):

Define mutations

A change in the genetic material of an organisim, usually in the DNA. They are a result of chance. Exposure to environmental factors called mutagens such as radiation or smoking can increase the chance of a somatic mutation occurring


Define somatic mutations

Mutations that occur in all the cells in the body except the sperm cells or the egg cells, therefore impossible to pass onto offspring. For example lung cancer from smoking or melanoma.


Define gametic mutations

Gametic mutations occur in the germ cells, meaning they are produced in the sex cells and can be passed onto offspring. An example in breast cancer being passed down the generations in a family.


Define a homologous chromosome

They are pairs of chromosomes which are identical in length and shape and have the same genes. One of them is from the mother the other is from the father


Define a diploid

The normal number of chromosome within a human body cell (46)


Define a phenotype

a physical expression of the genotype, eg curly brown hair or green eyes


Define a genotype

The combination of two different alleles eg Bb to make brown hair to become the phenotype


What is a dominant and recessive allele

A dominant allele has a capital letter B to be the dominant genotype to be expressed, the recessive allele is the lower case b which are over run by dominant alleles unless all alleles are recessive (homozogous)


Define Hetrozygous

Two different alleles which creat different genotypes, eg Aa


Define homozygous

the same type of allele, eg bb or B


Define an allele

Different forms of the same gene. Alleles are dominant and/or recessive


what is co-dominance

both genes are dominant and both alleles are equally and independently expressed. This causes a mix and creates roan cows


Define incomplete dominance

both genes are recessive eg rr wr. The result of it is the heterozygous alleles blend the two traits


What is a gene pool

A set of all the genes or genetic information in any population, usualy of a particular species


Define meiosis

The process of cell division that occurs in the ovaries and testes and makes the sex cells ova and sperm (gametes). Basically its the mixing of allele combination to form new ones, in two phases


What is incomplete dominance

One allele does not completely dominate over the other and a new phenotype is made by blending the two genotypes together eg a red snapdragon flower and a white snapdragon flower crossed making a pink snapdragon offspring.


what is a linked gene

genes located on the same chromosome and tend to be inherited together, this reduces genetic variation in the offspring when crossing over occurs.


What is a monohybrid cross?

A cross of only one gene eg brown hair dominant (B) and black hair recessive (b) which makes a 2x2 punnet square with a 1:1 genotype/phenotype ratio


Define a lethal allele

they are mutations of a gene that produce a non-functional gene product which may affect the organisms survival


What is recombination

The exchange of alleles between homologous chromosomes as a result of crossing over. Recombinations increase the genetic variation in the offspring.


What is crossing over

The exchange of genes between homologous chromosomes, resulting in a mixture of parental characteristics in the offspring and larger genetic variation


Define a homologous chromosome

A homologous chromosome is a pair and half of it comes from the mother and the other half comes from the father. Homologous chromosomes are similar, each carries the same genes in the same order, but the alleles for each trait may not be the same.


natural selection: what is stabilising selection

phenotypic extremes are selected against, reducing variations in a populations, happens most the time in populations to prevent a difference in a form of function such as birth weight in infants


natural selection: what is directional selection

the adaptive phenotype is shifted in one direction and one phenotype is favoured over the other, this could happen because of a change of environment


natural selection: what is disruptive selection

Disruptive selection favours two phenotypic extremes at the expense of the intermediate form, increasing the variation in a population.


What is a bottleneck

population bottlenecks occur when population numbers and diversity fall dramatically although a populations number may recover, often its genetic diversity does not


What is a dihybrid cross?

A cross of two different genes in a punnet square, eg Rwrw which makes a genotype and phenotype ration of 9:3:3:1. When making a dihybrid cross on a punnet square, all combinations of alleles will be made eg Rw, Rw, rw, rw