Biology- genetic variation words L2

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Allele

An alternative form of a gene

Centromere

The area where chromatids are joined together during meiosis

Chaisma

The point of contact between chromatids of homologous chromosomes during crossing over

Chromatid

One of two copies of a replicated chromosome produced during cell division. Each chromatid becomes a new chromosome in the cells produced during cell division

Chromosome

Thread-like structure in the nucleus made of DNA and protein that carries the genetic information. In human body cells there are 46 chromosomes (23 pairs)

Diploid

Having two sets of chromosomes

DNA

Deoxyribonucleic acid – the double helix molecule that carries the genetic code for each organism

Dominant allele

An allele that is always expressed phenotypically; even if the recessive allele is present 

Gamete

A sex cell e.g. sperm or egg

Gene

A length of DNA that codes for a particular characteristic or protein. Usually there are two of more forms (alleles) for a gene.

Genotype

The particular combination of alleles an individual possesses

Haploid

Having one set of chromosomes

Lethal Gene

Certain combinations of alleles cause death

Locus

The position of a gene on a chromosome

Phenotype

The physical expression of genes i.e. What an individual looks like due to their genes

Sex chromosomes

Chromosome involved in the determination of sex

Variation

Differences between individuals in a population

recessive allele

An allele that is only expressed if there are two copies of it present in an individual

Sex chromosome

Chromosome involved in the determination of sex

Somatic mutation

Mutations that occur in the DNA of regular body cells (somatic cells). These are not passed on to the next generation.

Linked genes

Occurs when genes are inherited together because they are found on the same chromosome and cannot separate independently

gametic mutation

Mutations that occur in the DNA of sex cells. These can be passed on to the next generation (if that gamete is fertilised)

crossing over

The exchange of genetic material between homologous chromosomes during meiosis

adaptation

Characteristics of organisms that increase their chances of survival

recombination

The rearrangement of alleles that occurs due to crossing over in meiosis

recombination result

New allele combinations that are formed during meiosis due to crossing over