3.4 + 10.2 Inheritance Flashcards
Mendel’s discoveries and conclusions
Discoveries:
- when purebreads were crossed only one characteristic appeared
- when Mendel self-fertilised the offspring - characteristics resulted in 3:1 ratio
Conclusions:
- organisms have discrete factors that determine features
- organisms posses two versions of each factor
- gamete contains only one version of each factor
- parents contribute equally to characteristics of offspring
- for each factor one version is dominant against another, so it will be complete;y expressed
Mendelian rules
- Law of segregation: when gametes form, alleles are separated, so each gamete carries only one allele
- Law of independent assortment: segregation of alleles for one characteristic occurs independently from other alleles (not true for genes on the same chrom. - linked genes)
- Principle of dominance: recessive alleles will be masked by dominant (not all genes show dominant hierarchy - co-dominance, incomplete dominance)
Why do gametes acrry only one allele?
Because gametes are haploid - one chromosome - only one allele present
What is the male genotype of sex chromosomes?
Hemizygous - males have only one allele on sex chromosomes
Types of zygosity
- homozygous
- heterozygous
- hemizygous
Define genotype
GENOTYPE: gene composition for a specific trait
Characteristics are determined by both genotype and environment
Define co-dominance
CO-DOMINANCE: when both alleles are expressed equally in the phenotype of a heterozygous organism - altered phenotype
example of co-dominance
BLOOD GROUPS: human RBC can be categorised into different groups based on glycoproteins (antigen) on tehir surface
Isoantigens:
A, B - codominant
O - recessive
Monohybrid cross
Genotypes of genetic disease
- autosomal recessive (both alleles needed)
- autosomal dominant (one or two alleles)
- co-dominant (one allele needed) but heterozygous milder symptoms than homozygous
Explain cystic fibrosis
- autosomal recessive, mutation in CFTR gene on chromosome 7
- individual produces mucus which clogs airways and secretory ducts in digestion system -> rwspiratory failure and pancreatic cysts
Explain Huntington’s disease
- autosomal dominant, mutation in Huntingtin gene on chrom. 4 - around 40 CAG repeats causes Huntingtin protein misfold - neurodegeneration
- usually in late adultohood
What are sex linked genes?
SEX LINKED GENES: genes which are located on sex chrom.
Sex linked conditions usually on X chrom, as Y chrom very short - not many genes present
X linked recessive traits more common in men - only one X chrom (no balance of dom) - only females can be carriers
Examples of X linked recessive conditions
- red-green colour blindness: mutation of red green photoreceptors on X chrom.
- haemophilia: body’s ability to control blood clotting is impaired - coagulation factor genes on X chrom
Define mutagens and their types
Mutagens - agents which increase the rate of mutations
- UV
- Radiation
- Biological (bacteria, viruses)
What is a pedigree chart?
PEDIGREE CHART: chart representing genetic history of a family over several generations
Males - squares
Females - circles
Horizontal line - mating
Oldest on the left
Dihybrid cross Punett grid
Ratios 9:3:3:1 if two heterozygotic for both phenotypes crossed
Unlinked genes vs linked genes Punett grid
Example of linked gene in Drosophilla
How can an offspring have a different allele than the parents?
An offspring has a recombinant gene - after corssing over i meiosis 1 of non-sister chromatids
Recombinant allele frequency is population compared to non-recombinant
Recombinant alleles are less common - corssing over is random - the further are two genes on homologous chromatids - the more likely is that recombination - more place for chiasmata to form
Phenotype differences in linked vs unlinked genes (AaBb x aabb)
Explain chi suqared test
Chi squared - statistical measure that determines whether difference between observed and expected frequency distribution
Steps:
- create hypotheses (null vs alternative)
- construct a table with observed vs expected frequencies
- apply chi formula:
- determine the degree of freedom (df): df = (rows-1) (columns-1)
- identify p value (p<0.05 - difference unsignificant - results reliable)
Monogenic vs polygenic inheritance
MONOGENIC: (phenotype controlled by single loci) - exhibit discrete variation in phenotypes (sex)
POLYGENIC: (phenotype controlled by several loci) - exhibit continuous variation in phenotypes (height, skin colour, eye colour)
Increase in number of gene loci that contribute to phenotype - more different exhibited - _Gaussian (bell-shaped) distributio_n
Charactertics not only detemrined by genetics but also by environment - skin colour
