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1

Genetics

A branch of biology that studies heredity and variation in organisms

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Heredity

Passing on of traits/ characteristics from one generation to the next

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Gene

A section of DNA (series of nucleotides/ bases) that controls a hereditary characteristic (trait), I.e. It is the basic unit of heredity in living organisms

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Gene pool

All genes, or genetic information, in a population of sexually reproducing organisms

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Hox genes

Master control genes that determine the way in which the body develops from a single zygote

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Epigenetics

The control of genes

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Genotype

Made up of all the genes an organism carries on its chromosomes which it has inherited from its parents

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Phenotype

The physical appearance of an organism

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Housekeeping genes

Genes active in many cell types which make proteins needed for basic functions

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Homozygous

Pair of alleles at the locus are the same for a particular trait

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Heterozygous (hybrid)

Pair of alleles a locus are different for particular trait

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Monohybrid cross

Cross between parents with different alleles for a single gene

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Generations

P1- parent generation
F1- first filial generation of offspring
F2- second filial generation of offspring

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Pure breeding plants

Plants that always give rise to offspring that are similar to themselves

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Complete dominance

A characteristic that is fully expressed in the phenotype of a heterozygous organism is the dominant allele

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Mendel's law of segregation

During meiosis, allele pairs separate (segregate) so that gametes have a single allele for each characteristic

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Mendel's law of dominance

In a cross of parents that are pure for contrasting traits, only the dominant trait will appear in the phenotype.
Recessive alleles will always be masked by dominant alleles

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Mendel's law of independent assortment

The alleles of different genes segregate randomly and independently of one another during gamete formation

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Haemophilia

Rare, genetically determined condition of frequent, excessive bleeding as the blood clots very slowly

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Polygenic inheritance

More than one pair of alleles responsible for a single trait

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Continuous variation

Graduations of a characteristic in a phenotype (e.g. height in humans)

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Mutation

Sudden change in the genetic make-up (DNA) of an organism

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Mutagen

Factors that increase the rate of mutations, e.g. environmental factors such as ionizing radiation (UV/ X-Ray), mutagenic chemicals (benzene and carbon tetrachloride), viruses and micro-organisms

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Neutral mutations

Do not affect life of the organism

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Autosomal

Related to chromosomes that are not sec chromosomes

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Albinism

Rare group of inherited genetic disorders that cause the skin, hair or iris of eyes to have little or no colour due to partial or complete absence of the pigment, melanin

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Carrier

Has a recessive allele and a dominant alleles in each cell, therefore has a normal phenotype

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SNP

(Single nucleotide polymorphism)
-biological markers
Genetic variations in a DNA sequence that occur when a single nucleotide is substituted for another nucleotide

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Genome

Complete set of genetic instructions (genes) necessary to create an organism

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HGP

-human genome project
International scientific research project set up in 1990