B11 - Inheritance Flashcards
Inheritance
The transmission of genetic information from generation to generation
Chromosomes
Located in the nucleus, they are thread-like structures of DNA, carrying genetic information in the form of genes
Gene
A short length of DNA found on a chromosome that codes for a specific protein
* control our characteristics as they code for proteins and play roles in what cells do
Alleles
Different versions of a particular gene
* like blood types
* they give all organisms their characteristics
Sex chromosomes
Males: XY
Females XX
* therefore, the father is responsible for determining the sex of the child
Karyotype
An individual’s complete set of chromosomes
Haploid nucleus
A nucleus containing a single set of unpaired chromosomes
* e.g. in gametes with 23 chromosomes
Diploid nucleus
A nucleus containing two sets of chromosomes
* e.g. in body cells with a pair of 23 chromosomes (46 overall)
Punnet square
A table in which all of the possible outcomes for a genetic cross between two individuals with known genotypes are given
* one pair of alleles on x and an other on the y-axis
* their combinations give us the ratios of the possible outcomes
Mitosis
Nuclear division giving rise to genetically identical cells
Process of mitosis
- Just before mitosis, each chromosome in the nucleus copies itself exactly (forms x - shaped chromosomes)
- Chromosomes line up along the centre of the cell where cell fibers pull them apart
- The cell divides into two; each new cell has a copy of each of the chromosomes leaving all resulting cells as a diploid nucleus
Where does mitosis occur? (3)
- Growth: produces new cells
- Repair: replace demaged or dead cells
- Asexual reproduction: produces offspring that are genetically identical to parent
Stem cell
Unspecialised cells used to divide by mitosis and produce new daughter cells that can become specialised
Meiosis
Nuclear division that gives rise to cells that are genetically different
* used to produce gametes
* is a reduction division: chromosome number is halved from diploid to haploid
Process of meiosis
- Each chromosome makes identical copies of itself (forming X-shaped chromosomes)
- First division: chromosomes pair up along the centre of the cell, recombination occurs and then cell fibres will pull the pairs apart, each new cell will have one of each recombinant chromosome pair
- Second division: chromosomes will line up along the centre of the cell, cell fibres will pull them apart (as with mitosis)
- A total of four haploid daughter cells will be produced
Differences between mitosis and meisos (name 3)
Mitosis:
* two cells produced (daughter cells)
* daighter cells are diploid
* daughter cells are genetically identical to each other and to parent cell
* one cell division occurs
Meisois:
* four cells produced (daughter cells)
* daughter cells are haploid
* daughter cells are genetically different from each other and parent cell
* two cell divisions occur
Phenotype
The observable characteristics of an organism (seen just by looking - like eye colour, or found – like blood type) is called the phenotype
Genotype
The combination of alleles that control each characteristic
* the genetic makeup of an organism in terms of the alleles present
Homozygous
Having two identical alleles of a particular gene (e.g. TT or gg)
Heterozygous
Having two different alleles of a particular gene (e.g. Tt or Gg)
Dominant allele
Will be expressed in phenotype if it is present
* shown through a capital letter in genotype
Recessive allele
Only expressed when no dominant allele of the gene is present
* shown through a small letter in genotype
Monohybrid inheritance
Monohybrid inheritance is the inheritance of characteristics controlled by a single gene
* when two homozygous parents of the same species, breed, the offspring will be pure bred?
Variation
Differences between individuals of the same species
Phenotypic variation
The difference in features between individuals of the same species
Genetic variation
The difference in DNA sequences between individuals within a population
Continuous variation
When there are very many small degrees of difference for a particular characteristic between individuals and they are arranged in order and can usually be measured on a scale
* height, mass, finger length etc.
Discontinuous variation
When there are distinct differences for a characteristic
* blood group, male or female, can they roll theur tongue etc.
Causes of phenotypic variation
- Genetic - controlled entirely by genes
- Environmental - caused by the environment in which the organism lives
Examples of genetic variation (name 3)
- blood group
- eye colour
- gender
- ability to roll tongue
Examples of environmental variation (name 2)
- An accident may lead to scarring on the body
- Eating too much and not leading an active lifestyle will cause weight gain
- Being raised in a certain country will cause you to speak a certain language with a certain accent
- A plant in the shade of a big tree will grow taller to reach more light
Cause of discontinuous variation
Usually caused by genetic variation alone
Cause of continuous variation
A combination of genetic and environmental causes
Mutations
A change in a gene or chromosome
Exposure to what can cause mutation? (3)
- Ionising radiation (e.g. gamma rays and X - rays) - which can damage bonds and cause changes in base sequences
- Some non-ionising radiation (e.g. ultra-violet) - can also damage bonds and cause changes in base sequences
- Certain types of chemicals - for example chemicals such as tar in tobacco
Sources of genetic variation in populations
- Mutations
- New alleles form through random changes to DNA
- Meiosis
- New allele combinations form through segregation
- Random mating
- Which partnerships form for sexual reproduction
- Random fertilisation
- Which sperm and egg combinations occur during sexual reproduction
Adaptive features
The inherited functional features of an organism that increase its fitness
Fitness
The probability of an organism surviving and reproducing in the environment in which it is found
Natural selection
The greater chance of passing on of genes by the best-adapted organisms.
Describe the process of natural selection (or the ‘survival of the fittest’) (6 steps)
- Individuals in a species show a range of variation caused by differences in genes
- When organisms reproduce, they produce more offspring than the environment is able to support
- This leads to competition for food and other resources which results in a ‘struggle for survival’
- Individuals with characteristics most suited to the environment have a higher chance of survival and more chances to reproduce
- Therefore the alleles resulting in these characteristics are passed to their offspring at a higher rate than those with characteristics less suited to survival
- This means that in the next generation, there will be a greater number of individuals with the better adapted variations in characteristics
Process of adaptation
Over generations, those features that are better adapted to the environment become more common
Describe the process of adaptation through the development of antibiotic resistance by bacteria
- A population of bacteria in the gut where some have antibiotic resistance
- When exposed to an antibiotic, bacteria causing illness as well as healthy gut bacteria are killed
- With reduced competition for nutrients, antibitotic resistance bacteria multiply, forming a larger population that is difficult to control
Selective breeding
To select individuals with desirable characteristics and breed them together
* has to be repeated for many successive generations before having a ‘new breed’
Differences between natural selection and artifitial selection (3)
Natural selection:
* Occurs naturally
* Results in development of population with features that are better adapted to their environment and survival
* Usually takes a long time to occur
Artificial selection:
* Only occurs when humans intervene
* Results in development of populations with features that are useful to humands and not necessarily to survival of the individual
* Takes less time as only individuals with the desired features are allowed to reproduce
