NA. 6.2 Patterns of Inheritance Flashcards
Define Phenotype
The expression of an organism’s genetic constitution combined with its interaction with the environment
Define Genotype
the Genetic material of an organism
How can Meiosis bring about Genetic Variation?
- Random arrangement of chromosomes during lining up.
* Crossing over of chromatids before the first division.
How does random fertilisation bring about Genetic Variation?
Gametes are haploid cells, meaning they only contain half of a person’s DNA. As this is determined by meiosis, every gamete contains different DNA. Therefore the same two individuals can produce genetically different offspring.
What is a Mutagen?
certain physical or chemical agents that can cause a mutations
When in the cell cycle is Gene/ DNA Mutation most likely to occur?
the S phase, when DNA is synthesized and replicated
When in the cell cycle is Chromosome Mutation most likely to occur?
during meiosis stages of Metaphase or Anaphase
crossing over and separation
What are the Chromosome Mutations?
- deletion, part of chromosome deleted
- inversion, section breaks off inverts then reattaches
- translocation,section attaches to another chromosome
- duplication, piece of chromosome duplicated
What’s Discontinuous Variation?
variation that can be assigned a particular category
e.g blood type
What’s Continuous Variation?
variation where differences in phenotypic features are quantitative
e.g height, weight
What’s an Allele?
the different versions of a gene
Homozygous?
having different alleles at a certain locus on a pair of homologous chromosomes
Heterozygous?
having the same alleles at a certain locus on a pair of homologous chromosomes
What is Monogenic Inheritance?
when a characteristic(phenotype) is determined by One gene
Define Dihybrid Inheritance.
Where two phenotypic characteristics are determined by two different genes present on two different chromosomes at the same time.
What is meant by multiple Alleles?
characteristics for which there are more than two alleles in the populations gene pool
What is meant by Codominant Alleles?
Two dominant alleles that both contribute to the phenotype, either by showing a blend of both characteristics, or the characteristics appearing together.
What is meant by Sex-linkage?
Where an allele is located on one of the sex chromosomes, meaning its expression depends on the sex of the individual.
What is an Autosome?
the 22 pairs of fully homologous chromosomes
How many Chromosomes do humans have?
23 total pairs of chromosomes where;
22 pairs are Autosomes
1 pair are the sex chromosomes
What is meant by Autosomal linkage?
Gene loci presents on the same autosomes that are usually inherited together
What does the term Linked suggest
when two or more gene loci are on the same chromosome
What is the Definition of Epistasis?
Where two non-linked genes interact, with one gene either masking or suppressing the other gene.
Whats is the Epistatic gene?
the Gene that can suppress or mask the expression of another gene at a different locus
Whats is the Hypostatic gene?
the Genes which expression can be affected by the epistatic gene
What is the Chi-squared test?
A statistical test to find out whether the difference between observed and expected data is due to chance or a real effect. Can be used to compare expected phenotypic ratios with observed ratios.
When can the Chi test be used?
- when the sample size is large
- if the data are raw counts( no percentages or ratios strictly number of individuals that fit categories)
- there are NO zero counts in the raw count data
What does the Null hypothesis state?
There is No statistically significant difference between the observed and expected data, hence and difference is due to chance
How can the number of genes coding for a characteristic influence variation?
- Discontinuous variation= characteristic determined by one gene (monogenic inheritance)
- Continuous variation= characteristic determined by more than one gene (polygenic inheritance)
What is Stabilising selection?
Occurs when environmental conditions stay the same so Individuals closest to the mean are favoured, and any new characteristics are selected against.
Results in low diversity.
What is Directional selection?
Occurs when environmental conditions change. Individuals with phenotypes suited to the new conditions will survive and pass on their genes. Over time the mean of the population will move towards these characteristics.
What is Genetic drift?
A change in a population’s allele frequencies that occurs due to chance rather than selective pressures.
What is meant by a Genetic bottleneck?
Where a catastrophic event dramatically reduces the size of a population, thereby decreasing the variety of alleles in the gene pool and causing large changes in allele frequencies.
What is meant by the founder effect?
When a small number of a original population in a new area form a new population with a limited gene pool, with allele frequencies not reflective of the original population.
What is the Hardy-Weinberg principle?
Allows us to estimate the frequency of alleles in a population, as well as if allele frequency is changing over time.
P=dominant allele frequency
Q=recessive allele frequency
Hardy-Weinberg equation for calculating allele frequency?
p+q=1
Hardy-Weinberg equation for calculating genotype frequency?
p2 + 2pq + q2 = 1
Define speciation.
Where a population is split and isolated, there are different selective pressures on the two groups. If the genetic makeup changes to the extent the two groups can not longer interbreed, they have become separate species.
What is Allopatric speciation?
Speciation resulting from a physical barrier, The environments occupied by the two groups are different, and therefore different alleles are favoured.
What is Sympatric speciation?
Speciation resulting from a non-physical barrier
Any changes in anatomy or behaviour may also prevent breeding.
What are the two types of Isolating mechanisms
geographical, results in allopatric (physical separated)
reproductive, results in sympatic (biological and behavioral)
What is Artificial selection?
Humans choose particular organisms to breed together in order to produce a desired characteristic in the offspring.
Give examples of Artificial selection in plants and animals.
- Plants= seeds used from plants that produce larger fruit and vegetables.
- Animals= cows with higher milk yield or more muscle are chosen and selectively bred.
Why is it important to keep a resource of genetic material when selective breeding?
Allows any traits that were accidentally bred out to be reintroduced, or to revert back to a point before any negative traits were introduced.
Give some ethical issues around the use of artificial selection.?
- Anatomical changes in animals e.g. respiratory issues in pugs, coat colours liked be people not suited to the wild
- Higher susceptibility to disease in both plants and animals, often due to inbreeding and lack of genetic variation
- Behavioral changes in domesticated changes may put them at disadvantages in the wild, e.g, more playful/docile, loss of nervous disposition
What’s a Selection pressure?
external agents which affect an organism’s ability to survive in a given environment
• Resource availability – Presence of sufficient food, habitat (shelter / territory) and mates
• Environmental conditions – Temperature, weather conditions or geographical access
• Biological factors – Predators and pathogens (diseases)
What is Inbreeding depression?
• Inbreeding depression is when related individuals are crossed
what is Hybrid vigour?
• Hybrid vigour is when breeders outcross to different varieties to produce individuals that are heterozygous at many loci, acts as a way to prevent inbreeding depression
why are Gene Banks incredibly important?
they store genomes in their organism, acts as a protective measure in case of the threat of extinction
what are some Gene Bank examples?
- Seed Banks & Sperm Banks
- Frozen embryos, cells in a tissue culture
- Botanic gardens & zoos
- rare breed farms
Physical Mutagenic agents?
if its a type of Rays and light
e.g UV, Gamma, Xrays
Chemical Mutagenic agents?
chemicals :)
acids, amines, gas
Biological Mutagenic agents?
Some viruses, food contaminants, transposons
who is referred to as the ‘Father of Genetics’
Gregor Mendel
