Genetics And Inheritance Flashcards
What is a genotype
The genetic constitution of an organism. All the alleles that an organism possesses.
What is a gene pool
All the alleles within an interbreeding population at a specific time
What is a phenotype
The expression of the genotype and its interaction with the environment (e.g.physical appearance)
What is an allele
Different versions of the same gene. Can be dominant, recessive or codominant
Homozygous
Same allele
Heterozygous
Different alleles
Define dominant allele
It is ALWAYS expressed in the phenotype
Define recessive allele
Only expressed in the phenotype if the genotype is HOMOZYGOUS
Codominant allele
Equally expressed within the phenotype
What does the hardy Weinberg principle state
The alleles frequency will remain constant from one generation to the next if :
- mating is random
- there is no mutations
- there is a large population
- zero migration
- no change in selection pressures
What does allelic frequency mean
The number of times an allele occurs in a gene pool
In the hardy Weinberg principle what is the letter for the dominant allele
P
What is the letter that represents the recessive allele in the hardy Weinberg principle
q
What are the 2 hardy Weinberg equations we need to know
P + q = 1
P2 + 2Pq + q2 = 1
What is monohybrid inheritance
The inheritance of a single gene which determines a single characteristic
Gene expression is
…which protein is being synthesised
What is a gene
A gene is a section DNA that codes for a specific protein
Ratio for monohybrid inheritance
3:1
Ratio for codominance
1:2:1
Rules for dominant and recessive
Dominant:
Unaffected parents can only have unaffected offspring
Affected offspring must have at least one affected parent
If both parents are unaffected and produce an affected offspring both parents must be heterozygous
Recessive:
Unaffected parents can have affected offspring if they are heterozygous
Sex linage rules
Dads and daughters (recessive):
If daughter is affected (homozygous recessive)
And Her father is not
And it is a recessive disease
It is not sex linked
Mums and sons (dominant):
If the son is affected
But the mother is not (homozygous recessive)
And it is a dominant disease
It is not sex linked
What is dihybrid inheritance
Involves a phenotype that is inherited as a result of two genes so two different characteristics
What is the ratio for dihybrid inheritance
9:3:3:1
What is the ratio for epistasis
9:4:3
15:1
9:7
All add to 16 but dot show 9:3:3:1
State three causes of genetic variation
• Mutation
• Crossing over
• Independent segregation / assortment (of homologous chromosomes)
• Random fusion of gametes / fertilisation / mating
What is meant by a genome?
• (All) the DNA in a cell/organism;
• ‘(all) the ‘genes’/alleles’ ‘genetic material/code’ in a cell/organism/ person’
• ‘the total number of DNA bases in a cell/organism’
What is a gene pool?
• All the alleles in a population;
How do multiple alleles of a gene arise?
• mutations;
• which are different / at different positions in the gene;
In genetic crosses, the observed phenotypic ratios obtained in the offspring are often not the same as the expected ratios.
Suggest two reasons why.
• Small sample size;
• Fusion/fertilisation of gametes is random;
• Linked Genes; Sex-linkage / crossing over;
• Epistasis;
• Lethal genotypes;
What is meant by a recessive allele?
• Only expressed in the homozygote / not expressed in the heterozygote / not expressed if dominant present;1
What does Hardy Weinberg’s equation predict
• The frequency/proportion of alleles (of a particular gene);
• Will stay constant from one generation to the next/over generations / no genetic change over time;
• Providing no mutation/no selection/population large/population genetically isolated/mating at random/no migration;
Define epistasis
• The allele of one gene affects or masks the expression of another in the phenotype;
Describe why observed phenotypes don’t match expected values
• Fertilisation is random
• OR
• Fusion of gametes is random;
• Small/not-large population/sample;
• Selection advantage/disadvantage/lethal alleles;
Define codominance
• Both alleles expressed in the phenotype;
Rules for Dominant alleles
• Affected offspring MUST have at least one affected parent.
• Unaffected parents ONLY have unaffected offspring.
• If both parents are affected and have an unaffected offspring, both parents must be Heterozygous
Rules for recessive alleles
• Unaffected parents can have an affected offspring (if they are Heterozygous)
Male offspring are more likely than females to show recessive sex-linked characteristics. Explain why.
• (Recessive) allele is always expressed in males / males have one (recessive) allele;
• Females need two recessive alleles / females need to be homozygous recessive / females could have dominant and recessive alleles / be heterozygous;
Expected offspring phenotype ratios from heterozygous parents:
1. Monohybrid
2. Dihybrid
3. Epistasis
4. Autosomal linkage
Dominant : recessive
- 3:1
- 9:3:3:1
- 9:4:3 or 15:1 or 9:7
- 3:1 (no x over) (no other pattern other than 4 phenotypes with recombination of alleles)
What is meant by the term phenotype
• (Expression / appearance / characteristic due to) genetic constitution / genotype / allele(s);
• (Expression / appearance / characteristic due to) interaction with environment;
Explain how a single base substitution causes a change in the structure of a polypeptide
• Change in (sequence of) amino acid(s)/primary structure;
• Change in hydrogen/ionic/disulfide bonds;
• Alters tertiary/30 structure;
