HEREDITY Flashcards
Define heredity.
Passing of traits to offspring
Define chromosome
Thread-like structure in the nucleus which is made up of DNA coiled around proteins
Define gene
DNA segment located on a chromosome which codes for a single unit of inheritance (allows genetic information to be stored)
Define gene locus
Position on the chromosome where the gene is located
Define alleles
Different forms of the same gene located on the same gene locus on a pair of homologous chromosomes
Define phenotype
Observable characteristics of an organism, depending on the genotype of the organism
Define genotype
Genetic make-up of an organism that is determined by the existence of dominant and recessive alleles
Define homozygote
Organism with two identical genes at a locus / containing two identical alleles for a specific trait (TT or tt)
Define heterozygote
Organism with two different genes at a locus / containing two different alleles for a specific trait (Tt)
Define dominant allele
Fully expressed allele in the phenotype under both homozygous and heterozygous conditions.
Define recessive allele
Allele only expressed in the phenotype under the homozygous condition. Masked in the phenotype under heterozygous conditions
Define complete dominance
When the heterozygote has the same phenotype as the dominant homozygote. The recessive allele present in the heterozygote is masked by the dominant allele
Define co-dominance
When both alleles contribute equally to the phenotype
Identify which alleles are recessive and dominant: Iᴼ, Iᴬ, Iᴮ
Iᴼ: Recessive
Iᴬ: Dominant (co-dominant with Iᴮ)
Iᴮ: Dominant (co-dominant with Iᴬ)
Define incomplete dominance
When heterozygous individuals show an intermediate phenotype. This comes because neither allele is completely dominant over the other.
Define karyotype
Picture of a set of chromosomes in a cell. It will show 22 pairs of homologous chromosomes (autosomes) and 1 pair of sex chromosomes (XY)
What genotypes do males and females have?
M: XY
F: XX
Define mutation
Change in gene or chromosomal structure that typically occur during the replication of genes or chromosomes
How do mutations occur?
- Spontaneous mutations during the replication or repair of DNA
- Exposure to mutagens
Define mutagens
Physical or chemical agents that increase the rate of mutation.
(e.g. ultraviolet radiation, certain chemicals)
Define gene mutations
Mutation in genes typically linked to the X chromosomes
Define chromosome mutations
Mutations involving a change in the number/structure of chromosomes, occurring during meiosis or mitosis
What kind of mutation is albinism, and what is it?
Gene mutation.
Lack of pigmentation in skin, hair and eyes. It is caused by a mutation in a recessive allele which is involved in the production of pigments.
What kind of mutation is sickle-cell anaemia, and what is it?
Gene mutation.
Blood disorder where red blood cells possess a rigid, sickle shape when oxygen concentration in the blood is low.
1. Sickle cells are not flexible -> block blood vessels -> blood unable to deliver oxygen to tissues -> tissue damage
It is caused by a mutation in the gene that codes for a protein required for haemoglobin production.
What kind of mutation is down syndrome, and what is it?
Chromosome mutation.
Condition caused during meiosis, resulting in mental retardation, heart defects and respiratory defects.
How does down syndrome happen?
- Zygote inherits 3 copies of chromosome 21 instead of 2 -> mutation is present in all body cells due to mitosis during zygote development
- HENCE, each body cell contains 47 chromosomes instead of 46
Define genetic variations
Differences in phenotypes between individuals of the same species
Define discontinuous variation
When individuals possess distinct and separate phenotypes with no intermediates. This is controlled by alleles of a single gene or a small number of genes.
e.g. human blood group
Define continuous variation
When an unbroken range of phenotypes exists in the population (no distinct difference). This is controlled by the effect of many genes, and often affected by environmental factors.
e.g. intelligence, height, skin colour
Define evolution
Change in genetic material of a population from one generation to the next
Define natural selection
Major mechanism by which evolution takes place, causing helpful genes to become more common and deleterious genes to become rarer
What are some environmental factors that act as forces of natural selection?
- Disease (disease-resistant phenotypes would be selected)
- Prey (characteristics conductive to obtaining more food are selected)
- Predators (methods for evading predators are selected)
- Mating (features more attractive to females of the same species are selected)
Define artificial selection
Intentional breeding for particular genetic traits to produce several economically important crops and animals.
What is hybridisation?
- Two parents are selected, each of which possesses either one of two desirable traits
- Crossing these parents will create new hybrids with the preferred combination of genes
- Propagating these hybrids
What is inbreeding?
- Two parents are selected, each of which possesses either one of two desirable traits
- Crossing these parents will create new hybrids with the preferred combination of genes
- Breeding among closely related individuals
