6.2: Patterns of inheritance Flashcards
What are mutagens?
Increases the rate of mutations
What are physical agents of mutagens?
3x
- X rays
- Gamma rays
- UV light
What are chemical agents of mutagens?
3x
- Mustard gas
- Nitrous gas
- Benzopyrene (found in tobacco smoke)
What are biological agents for mutagens?
- Some viruses
- Transposons
- Food contaminants
What are persistent mutations?
Transmitted through many generations without change
What are random mutations?
Not directed by a need on the part of the organism in which they occur
What are five types of chromosome mutations?
- Deletion
- Inversion
- Translocation
- Duplication
- Non-disjuncture
What is deletion?
Part of a chromosome, genes and regulatory seuqences, is lost
What is inversion?
Sections of chromosome breakas off, turns 180 degrees and joins again
Some genes may be too far away from their regulatory nucleotides to be experienced
What is translocation?
Piece of chromosome breaks off, then becomes attached to another chromosome - interferes with the regulation of the gene
What is duplicaton?
Piece of chromosome is duplicated
Overexpression is harmful - too many of certain protiens/gene regulatory nucleic acids may disrupt the metabolism
What is non-disjunction?
One pair of chromosome fails to separate leaving one gamete with an extra chromosome
What is aneuploidy?
Chromosome number is not an exact multiple of the haploid number for that organism
Chromosomes/chromatids fail to separate during meiosis
What is polyploidy?
Diploid gamete fertilised by a haploid gamete, the rsulting zygote will be triploid (three sets of chromosomes)
How does genetic variation arise?
- Allele shuffling - swapping of alleles between non-sister chromatids, during crossing over in prophase 1
- Independent assortment of chromosomes - M1 AND A1
Independent assortment of chromatids - M2 AND A2
What does random fertilisation of gamtes that are already genetically unique produce?
Extensive genetic diversity among the resulting offspring
What is random fusion?
Any gamete can potentially combine with any female gamete from an organism of the same species
What are beneficial mutations?
Helped drive evolution through natural selection
Why were blue eyes a beneficial mutation?
Help people see better in less bright light in temperate zones
BUT
Harmful in areas where sunlight intensity is higher as a lack of iris pigmentation could lead to lens cataracts
Why was paler skin in temperate zones and darker skin in Africa benefical mutations?
High concentration of melanin protected early humans in Africa from sunburn and skin cancer
Temperate conditions: paler skin would be an advantge enabling vitamin D to be made with a lower intensity of sunlight - protects us from heart disease and cancer
What are neutral mutations?
Neither harmful or benefical
- Inability to smell certain flowers
- Differently shaped ear lobes
What are four types of variation?
- Interspecific
- Intraspecific
- Continuous
- Discontinuous
What is interspecific variance?
Between two species
What is intraspecific variance?
Within species
What is variation caused by?
Genetic differences or the influence of the environment
What is discontinuous variation?
Controlled solely by genetics
e.g human blood type
What is continuous variation?
Caused by multiple genes and the environment working together e.g height/mass of an organism
What are features of continuous variation?
- Presented in a histogram
- No distinct categories
- Data is quantitive
What are features of discontinuous variation?
- Two or more distinct categories
- No intermediates
What is etiolation?
Elongation of stem between node, occurs in shaded area to reach light
What is chlorosis?
Chlorophyll not produced
What is monohybrid inheritance?
Involves the transmission of one gene from parents to their offspring
Where does monohybrid inheritance occur?
Gametes (sex cells) because they are haploid, which means that they have one allele per gene
What do you have to show before drawing punnet square?
5 things
Parental genotypes: Rr x Rr
Parental phenotypes: round round
Gametes produced: Rr Rr
F2 genotypes:
- R R R r
- R r r r
F2 phenotypes: round round round round
What is F1 generation?
The offspring from individuals with homozygous dominant and homozygous recessive genotypes
All the offspring will be heterozygous, inheriting a recessive allele from one parent and a dominant allele from the other
The offspring in the F1 generation will therefore all express the dominant trait in their phenotype
What is the F2 generation?
Offspring from a two heterozygous F1 individuals
It results in offspring exhibiting a 3:1 ratio of dominant to recessive phenotypes, as shown above.
What is the genotypic ratio and phenotypic ratio for monohybrid inheritance?
Genotypic: 1:2:1 for RR:Rr:rr
Phenotypic: 3:1
What is dihybrid inheritance?
Inheritance of two genes therefore 4 alleles
What can dihybrid crosses help to do?
- Determine whether genes are linked
- Locate genes on specific chromosomes
- Calculate expected phenotypic ratios in subsequent generations
What is the ratio in dihybrid inheritance?
9:3:3:1
What are reason why the ratio deviates in dihybrid inheritance?
Random fertilisation:
* Gamete fusion is a chance process
* Small sample sizes can lead to skewed ratios, while larger samples minimise these random effects
Linked genes:
* Linked genes are on the same chromosome so alleles are usually inherited together, maintaining the parents’ original allele combinations in offspring.
* However, crossing over during meiosis can sometimes change these allele combinations by separating linked genes.
