Inheritance Flashcards
Define alleles
Different forms of the same gene
Define a genotype
Genetic information regarding the types of alleles present in a genome
Define a phenotype
The characteristics shown as a result of the genotype
Define a Dominant allele
If present at all, will show in the phenotype
Define a recessive allele
Must be present in homozygous form to show in phenotype
How is a recessive disease inherited
Parents being carriers by having one copy of the recessive allele
How can you test if an organism has a heterozygous or homozygous dominant genotype
A back cross
What is the mendelian ratio for monohybrid homozygous cross
1:2:1
What is the mendelian ratio for a dihybrid double heterozygous cross
9:3:3:1
How can a phenotype of co-dominance be expressed
As a mixed phenotype, eg, roan cattle that are patchy
As incomplete dominance, eg, pink carnations from white and red parents
How does linkage work
If two different genes are found on the same chromosomes there is a possibility for crossing over and so a Mendelian ratio is less likely
Name two conditions that are sex-linked
Duchenne Muscular dystrophy
Haemophilia
How do sex-linked conditions work
They are carried on the X chromosome and so if are present in a male genotype, will show in the phenotype. Females are often carriers and have male children with the conditions
Where are mutations more likely
In cells with short cycles
What phase of the cell cycle are mutations most likely in
S phase
What is translocation
Breaking off of part of all of a chromosome and attaching to another
Define triploid
Three sets of genetic information
Define polyploidy
Having multiple sets of chromosomes
Define non-disjunction
A faulty spindle causes chromosomes to not be shared equally in anaphase. This is a leading cause of chromosomal mutations
What is trisomy
Having three of the same chromosome
What is Down’s Syndrome caused by
Non-disjunction causing trisomy of chromosome 21
What are gene mutations
Much smaller and much more common than chromosomal mutations
Conditions caused by chromosomal mutations
Down’s syndrome
Patau Syndrome
Name common mutagens
Ionising radiation
Chemicals
Metals
Infectious agents
How might you be affected by having the alleles for sickle cell anaemia
Heterozygous genotype means you carry the trait and 30% of your blood cells are affected
Homozygous affected means 100% of your cells are affected and you have a decreased life expectancy
How do proto-oncogenes cause cancer
Mutations to these genes cause oncogenes which cause cancer through uncontrolled cell division by preventing programmed-cell death
How do tumour suppressor genes cause cancer
Mutations to these genes means damage is no longer repaired to DNA
Explain epigenetics
Pre-mRNA can be copied wrong, causing a change to the protein synthesised without a change to the DNA
What is X inactivation
epigenetic changes can switch off an entire chromosome
What is genomic imprinting
Inactivated genes in gametes can be transferred to the next generation
