6.2 - B - Patterns Of Inheritance Flashcards
What is a genotype?
What is a phenotype?
Genetic makeup of an organism
Visible characteristic of an organism
What are mutagens?
What do they do?
Certain physical and chemical agents.
Increase the rate of mutation.
Name 3 physical agents, chemical agents and biological agents
X rays, gamma rays, UV light.
Benzopyrene (tobacco smoke), mustard gas, nitrous acid.
Some viruses, transposons, food contaminants.
What are transponons
Jumping genes, remnants of viral nucleic acid that have become incorporated into our genomes
Mutations during gamete formation are:
Persistent - they can be transmitted through many generations without change.
Random - they are not directed by a need on the part of the organism in which they occur.
List and define the 7 types of chromosome mutations
Deletion - pieces of chromosomes are deleted.
Inversion - flipping 180°.
Translation - a piece of chromosome breaks off and then attaches to another chromosome.
Duplication - pieces of chromosomes are duplicates.
Non-disjunction - one pair of chromosomes/chromatids fails to separate, leaving one gamete with an extra chromosome. This causes Down syndrome.
Aneuploidy - chromosome number is not an exact multiple of the haploid number. Sometimes chromosomes/chromatids fail to separate during mitosis (eg. trisomy).
Polyploidy - if a diploid gamete is fertilised by a haploid gamete, the resulting zygote will be triploid. The fusion of 2 diploid gametes makes a tetraploid zygote.
What are the 3 points during meiosis where genetic variation may result from?
Allele shuffling (swapping of alleles between non-sister chromatids) during crossing over in prophase 1.
Independent assortment of chromosomes during metaphase/anaphase 1.
Independent assortment of chromatids during metaphase/anaphase 2.
What does random fusion of gametes create?
More genetic diversity
Define monogenic
Determined by a single gene
What is a gene locus
The position of a gene on a chromosome
Define heterozygous
Having different alleles at the same gene locus on a pair of homologous chromosomes
Define homozygous
Having identical alleles at the same gene locus on a pair of homologous chromosomes
Define true-bred
Homozygous
Define dominant
Masks the effects of recessive alleles (big letter)
Define recessive
Masked by dominant alleles (little letter)
Define F1
First generation of offspring (to original parents)
Define F2
Second generation (offspring of F1)
Which way round do the genders go on a Punnett square?
Females down side/males along top
Give 5 features of continuous data
No defined categories/distinct groups.
There is a range ‐ any value is possible.
Caused by more than one gene (polygenic)and often, the environment.
The greater the number of gene loci contributing to the characteristic, the greater the range in variation.
Quantitative.
Give 5 features of discontinuous data
Discrete categories with no intermediates.
Usually caused by one gene (mongenic).
Genes at different loci may interact to influence one characteristic and
cause discontinuous variation (epistasis).
No (very little) environmental effects cause it.
Qualitative.
What did Mendel base his study on?
Pea plants
Define dihybrid
Involving 2 gene loci
To use Chi squared the data must (3 things):
Be discontinuous categories only e.g. phenotypes.
Have a large sample size with no zeros in the counts.
Not be % or ratios ‐ raw counts only.
How is a gene locus described if it has 3 or more alleles?
Give an example
Having multiple alleles
ABO blood groups
Define co-dominance
Where both alleles present in a heterozygote contribute to the phenotype. The phenotype of a homozygote and heterozygote is different.
Define sex linkage
When a gene is present on one of the sex chromosomes
What are the human sex chromosomes in:
Women
Men
XX
XY
Why are sex chromosomes not fully homologous?
The Y chromosome lacks many of the genes that code for characteristics on the X chromosome. Males can be neither homozygous or heterozygous for these genes.
Give 2 examples of sex linkage
Haemophilia A
Colour blindness
Give an example of codominance in animals and one in humans
Cow coat colour
Sickle cell anaemia
Define autosomal sex linkage
When 2 (or more) genes on the same chromosome are inherited together ‐ they do not undergo independent assortment (in metaphase I)
Define epistasis
What does it reduce?
An interaction of non‐linked genes (on different chromosomes) where one masks the expression of the other.
The number of phenotypes in the F2 generation and so reduces variation.
What are epistatic alleles?
What are hypostatic alleles?
The alleles that are masking the effect of the alleles of the other gene are called epistatic alleles.
The alleles whose effect is being masked.
Define recessive epistasis
Where the homozygous recessive alleles of gene locus 1 are epistatic (prevent the expression of) to both alleles on gene locus 2 (hypostatic).
Define dominant epistasis
Where the dominant alleles of gene locus 1 are epistatic (prevent the expression of) to both alleles on gene locus 2 (hypostatic).
What can the Hardy-Weinberg principle be used to do?
Predict allele frequencies within a population
What are the 4 conditions that must be met for Hardy-Weinberg to be applied?
Large population.
Random mating.
No selective advantage for any genotype.
No gene mutation, migration or genetic drift.
Define population
Members of a species, living in the same place and at the same time, that can interbreed.
Explain the formulae of the Hardy-Weinberg principle
A = p a = q p + q = 1 Probability of AA = p^2 Probability of aa = q^2 Probability of Aa = 2pq So: p^2 + q^2 + 2pq = 1
What is the chi-squared test?
Statistical test designed to find out if the difference between observed and expected data is significant or due to chance
A modification of what shows you epistasis?
Any modification of a 9:3:3:1 phenotypic ratio
Describe the stages in natural selection
Mutations (and migration) lead to variation in population as they
introduce new alleles.
Competition to survive between individuals.
Those with best adaptations survive, breed and pass on advantages
alleles causing adaptations.
The frequency of this allele increases over generations.
What are the 2 types of natural selection?
Stabilising selection
Directional selection
Explain stabilising selection
Natural selection leading to constancy within a population. Intermediate phenotypes are favoured over extremes. Alleles for extreme phenotypes may be removed from the population. Stabilising selection reduces genetic variation within the population. Occurs when the organisms’ environment doesn’t change.
E.g. animals with very short/long fur in constant temperatures will be selected against ‐ those with mid length fur will survive ‐ higher frequency of alleles for mid length fur.
Explain directional selection
A type of natural selection that occurs when an environmental change favours a new (extreme) phenotype and so results in a change in the population mean.
E.g. climate temperature decreases. Those with long fur survive, breed and pass on allele for long hair ‐ over time this allele becomes more frequent in population.
Define genetic drift
Explain it
Random changes in allele frequency in small populations.
It happens in a small population (with a small gene pool).
Chance mutations that are neither beneficial/harmful cause change in
frequency of alleles.
The population alleles can ‘drift’ from original.
Where does genetic drift only happen?
Why?
Only happens in small populations because each individual forms a larger proportion of the gene pool and therefore has a greater effect on the gene pool. It is also easier to ‘lose’ a gene from a small gene pool.
What are the 2 special types of genetic drift?
Founder effect
Genetic bottleneck
Explain the founder effect
When a small number of individuals from an original larger population establish a new population by moving to a new area. The gene pool is not as diverse as that of the parent population.
Some alleles lost from population at random (these could be
advantageous).
Genetic variation reduced ‐ genetic drift.
Explain genetic bottleneck
A sharp reduction in size of a population due to environmental catastrophes such as earthquakes, floods, disease or human activity which reduce genetic diversity. As the population expands it is less genetically diverse as before.
Define speciation
The splitting of a population of a species into 2 isolated populations that over time undergo genetic changes which result in reproductive isolation and therefore the formation of 2 different species.
What are the 2 types of isolating mechanisms that cause speciation?
What types of speciation do they lead to?
Geographical isolation leads to allopatric speciation
Reproductive isolation leads to sympatric speciation
Explain how geographical isolation leads to allopatric speciation
Populations are physically separated e.g. by water/mountains/fences.
Barrier prevents gene flow between populations.
Genetic changes occur in species caused by genetic drift, mutations or natural selection (different pressures in different areas).
Ultimately the populations become genetically so different they can no longer interbreed to produce fertile offspring (reproductively isolated) ‐ new species have been formed.
Explain how reproductive isolation leads to sympatric speciation
Several things can lead to individuals in a population becoming reproductively isolated:
Behavioural changes e.g. changes to sleep patterns, courtship behaviours,
Biological changes e.g. size differences, genetalia differences,
Genetic changes e.g. change in chromosome number prevents zygote viability.
Once populations can no longer interbreed to produce fertile offspring
(reproductive isolation) ‐ new species have been formed
Define artificial selection
Selective breeding of organisms in order to produce desired
phenotypes in an organism ‐ often of benefit to humans
Humans chose parents with desired phenotypes and therefore the desired alleles and interbreed them to produce offspring with higher frequency of these phenotypes. Repeated over many generations.
What are the 4 stages in artificial selection?
Male and female with desired characteristic chosen.
Male and female interbred.
Best offspring selected and interbred.
This is repeated over many generations.
Give an example of artificial selection in:
Animals
Plants
Best quality/highest yield of wool, meat, milk; speed of horses, appearance of dogs.
Best flavour/highest yield of crops, pest/drought resistance.
Define allopathic speciation
Define sympathetic speciation
Formation of 2 different species from one original species use to geographical isolation.
Formation of 2 different species from one original species, due to reproductive isolation, while the populations inhabit the same geographical location.
List the importance of maintaining a resource of genetic material for use in selective breeding including wild types (the original population you bred from)
Selective breeding tends to reduce the gene pool.
This could mean if there was a rapid environmental change e.g.
temperature/disease ‐ genetically similar e.g. crops would not have
the variation needed to survive.
We use gene banks to maintain a source of alleles for future breeding.
This can counteract the loss in genetic variation, inbreeding, and
extinction in the event of a disease etc.
It can also preserve currently unknown useful traits/alleles e.g. medicinal uses.
List the different types of gene banks
Seed/sperm/egg banks/embryo,
Rare breed farms,
Botanic gardens/zoos
Explain interbreeding
As the genetic diversity decreases with each generation, individuals become more and more related ‐ inbred.
The likelihood of unintentionally selecting 2 copies of a harmful recessive allele can increase in a small gene pool.
This can lead to increased susceptibility to disease.
To avoid this, breeders can ‘outcross’ individuals with their wild types (or individuals from gene banks) to prevent the gene pool becoming too small.
Explain the ethical considerations of selective breeding
Often doesn’t take into account animal welfare.
Inbreeding can increase susceptibility to disease e.g. some breeds are highly susceptible to cancers.
Many domesticated animals e.g. pigs would not survive if released into the wild ‐ easy prey, wrong fat:muscle ratio to survive in cold.
Explain when inbreeding depression occurs
At each stage of selective breeding, the individuals with the desirable characteristics and no or few undesirable characteristics are selected. Inevitably, the genetic diversity in the gene pool of the selected breed is reduced.
Inbreeding depression occurs when related individuals are crossed.
The chances of an individual inheriting two copies of a recessive harmful allele are. increased
Explain hybrid vigour
When breeders sometimes outcross individuals belonging to 2 different varieties to obtain individuals that are heterozygous at many gene loci
Explain the ethical considerations of artificial selection
Domesticated animals retain many juvenile characteristics, making them friendly, docile and playful, but less able to defend themselves. The loss of their nervous disposition can also make them easy prey.
Livestock animals selected to have more lean meat and less fat might succumb to low environmental temperatures during winter if they are not housed.
The traits in dogs, considered desirable by humans, might put the dogs at a selective disadvantage if they had to survive in the wild.
Some breeds, through inbreeding from a limited number of pedigree dogs, have susceptibility to disease.
Some coat colours, selected because humans like the look of them, would failed to camouflage the animals.
