Patterns Of Inheritance Flashcards
Genotype
The genetic makeup of an organism
Phenotype
The characteristics observed when the genotype interacts with the environment
Allele
Variations of genes which arise through mutation
Carrier
An organism which can pass an inherited genetic disease onto their children but are not affected by the disease
Heterozygous
Contains two different alleles
Homozygous
Contains two of the same alleles
Dominant
Only requires one for the characteristic to be expressed
Recessive
Requires all alleles to be recessive to express the gene
Huntington’s disease
Huntington’s disease is a condition that damages nerve cells in the brain causing them to stop working properly. It’s passed on (inherited) from a person’s parents. The damage to the brain gets worse over time. It can affect movement, cognition (perception, awareness, thinking, judgement) and mental health.
Cystic fibrosis
a hereditary disorder affecting the exocrine glands. It causes the production of abnormally thick mucus, leading to the blockage of the pancreatic ducts, intestines, and bronchi and often resulting in respiratory infection
How can meiosis bring about genetic variation
Random arrangement of chromosomes during lineup
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 persons DNA. As this is determined by meiosis, every gamete contains different DNA. Therefore the same two individuals can produce genetically different offspring
Define monogenic inheritance
Where one phenotype characteristic is controlled by a single gene
Draw a genetic diagram for monogenic inheritance
Parental phenotypes = Brown eyes, Blue eyes
Parental genotypes = Bb, bb
Gametes = B, b and b, b
Offspring genotypes = Bb, Bb, bb, bb
Offspring phenotypes = 2:2 brown eyes : blue eyes
Define dihybrid inheritance
Where two phenotypic characteristics are determined by two different genes present on two different chromosomes at the same time
Draw a genetic diagram for dihybrid inheritance
Parental phenotypes = Round yellow seeds, Wrinkled green seeds
Parental genotypes = RRYY and rryy
Gamates = RY, RY and ry, ry
Offspring genotypes = RrYy
Offspring phenotypes = Round yellow seeds
What is meant by sex-linkage
Where an allele is located on one of the sex chromasomes, meaning its expression depends on the sex of the individual
Draw a genetic diagram for sex-linked inheritance
Parental phenotypes = Carrier female and Normal male
Parental genotypes = XAXa and XAY
Gametes = XA, Xa and XA, Y
Offspring genotypes = XAXA, XAXa, XAY, XaY
Offspring phenotypes = Normal female, carrier female, normal male, affected male
What is meant by multiple alleles
A gene with more than two alleles
Draw a diagram for multiple allelic inheritance
Parental phenotypes = Blood group A and Blood group B
Parental genotypes = IAIO and IBIO
Gametes = IA, IO and IB and IO
Offspring genotypes = IAIB, IAIO, IBIO, IOIO
Offspring phenotypes = Group AB, Group A, Group B, Group O
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
Draw a genetic diagram for codominant expression
Parental Phenotypes = Red flower and white flower
Parental genotypes = cRcR and cWcW
Gametes = cR, cR and cW, cW
Offspring genotypes = cRcW
Offspring phenotypes = Pink flowers
What is meant by autsomal linkage
Where two or more genes are located on the same (non-sex) chromosome. In this case, only one homologous pair is needed for all four alleles to be present. For genes that aren’t linked, two homologous pairs are needed
What is meant by epistasis
Where two non-linked genes interact, with one gene either masking or suppressing the other gene
What is the chi-squared test
A statistical test to find out whether the difference between observed and expected data is due to change or a real effect
Can be used to compared expected phenotypic ratios with observed ratios
How is chi-squared test performed
The formula results in a number which is then compared to a critical value (for the corresponding degrees of freedom). If the number is greater than or equal to the critical value, we conclude that there is no significant difference and the results occurred 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, 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. Overtime the mean of the population will move towards these characteristics
What is genetic drift
A change in a population’s allele frequencies that occur due to chance rather than selective pressures. In other words, it is caused by ‘sampling error’ during reproduction
What is meant by a genetic bottleneck
Where a catastrophic event dramatically reduces the size of a population, therefore reducing the variety of alleles in the gene pool and causing large changes in allele frequencies
What is meant by the Founders effect
When a small numer of individuals become isolated, forming a new population with a limited gene pool, with allele frequencies not reflective of the original population
What is the Hardy-Weinburg principle
Allows us to estimate the frequency of the allels within a population as well as if allele frequency is changing overtime
Explain the Hardy-Weinburg equation for calculating allele frequency
The frequencies of each allele for a characteristic must add up to 1.0. The equation is therefore p + q = 1
Where p= frequency of the dominant allele and q= frequency of the recessive allele
Explain the Hardy-Weinburg equation for calculating genotype frequency
The frequencies of each genotype for a characteristic must add up to 1.0
The equation therefore is p^2 + 2pq + q^2
Where p^2 = frequency of homozygous dominant, 2pq= frequency of heterozygous and q^2 is the frequency of homozygous recessive
Define speciation
Where a population is split and isolated, there are different selection pressures on the two groups. If the genetic makeup changes to the extent the two species can no longer interbreed, then they have become separate species
What is meant by allopatric speciation
Speciation resulting from a physical barrier e.g. river, mountain range. The environments occupied by the two groups are different, and therefore different alleles are favoured
What is meant by sympatric speciation
Speciation resulting from a non-physical barrier - e.g. a mutation that no longer allows two organisms to produce fertile offspring. Any changes in anatomy or behaviour may also prevent breeding
What is artificial selection
Humans choose specific 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 which produce larger fruit and vegetables
Animals = cows with higher milk yield 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 issues in animals e.g. respiratory issues in pugs and other short snouted dogs
Higher susceptibility to disease in both plants and animals
