inheritance and populations Flashcards
Define gene
A sequence of bases on a DNA molecule that codes for a protein which results in a characteristics
Define allele
A different version of a gene with different base sequences and therefore different codes
Define genotype
The combination of alleles present within the cells of an organism
Define phenotype
The expression of the genotype results in observable biochemical characteristics and its interactions with the environment
Define dominant
An allele whose characteristics is expressed in the phenotype even though there is only 1 copy of it (heterozygous)
Define recessive
An allele whose characteristic only appears in the phenotype if 2 copies are present (homozygous)
Define codominant
Alleles that are both expressed in the phenotype in heterozygous conditions
Define locus
In the fixed position of a gene on a chromosome, alleles of a gene are found the at the same locus on each chromosome in a pair
Define homozygote
An organism that carries 2 copies of the same allele
Define heterozygote
An organism that carries two different alleles
Define carrier
A person carrying an allele which is not expressed in the phenotype but that can be passed on to the offspring
Define dipoloid organisms
Organisms that have 2 sets of chromosomes
How many alleles per gene do diploid organisms carry
2
Define gametes
They are sex cells that contain only 1 allele for each gene
How many alleles per gene do gametes carry?
1
Explain what happens when two gametes fuse together
- When gametes from two parents fuse together, the alleles they contain form the genotype of the offspring produced
- At each locus, the genotype can be homozygous or heterozygous.
What do genetic diagrams predict?
Predict the genotypes and phenotypes of the offspring produced if two parents are crossed
Define monohybrid inheritance
It is the inheritance of a phenotypic characteristic controlled by a single gene
What do monohybrid crosses show?
They show the likelihood of the different alleles of a gene being inherited by the offspring of certain parents
What do Punnet squares predict?
The genotypes and phenotypes of offspring
Define dihybrid inheritance
Where two phenotypic characteristics are determined by 2 different genes present on 2 different chromosomes at the same time
Define phenotypic ratio
It is the ratio of different phenotypes in offspring
Why do you not get the expected phenotypic ratios?
- Crossing over between chromatids produces different combinations of alleles
- Independent assortment produces different combinations of maternal and paternal alleles
What are the sex chromosomes in mammals?
- In females: XX
- In males: XY
What is meant by sex-linkage
Where an allele is located on one of the sex chromosomes, meaning its expression depends on the sex of the individual
Why are males more likely to express a recessive sex-linked allele?
- Most sex-linked alleles are located on the X-chromosome
- Males only get 1 copy of the allele, so will express this characteristic even if it’s recessvie
- Since females get 2 alleles, this is less likely
Which parent do males inherit sex-linked characteristics from?
- Their mother since the Y chromosome can only come from their father
- The mother is heterozygous for sex-linked alleles, she is a carrier and may pass the trait on
What are autosomes
Any chromosome that isn’t a sex chromosome
Where are autosomal genes found
On the autosome
What is meant by autosomal linkage?
Where 2 or more genes are located on the same (non-sex) chromosome
Explain autosomal linkage
- Genes are on the same autosome and stay together during the independent segregation of chromosomes in meiosis I
- Their alleles will be passed on to the offspring together
- The closer together the loci are on the autosome, the more closely they are linked because crossing over is less likely to split them up
What can prevent sex-linkage?
Crossing over because it seperates the genes on the autosome
What is meant by epistatsis?
Where two non-linked genes interact, with one gene either masking or suppressing the other gene
Define 2 types of epistasis
- Recessive epistasis = two homozygous recessive alleles at the first locus mask expression of another allele at the second locus
- Dominant epistasis = where 1 dominant allele on the first locus masks expression of multiple other alleles at the second locus
What is the chi-squares test?
A statistical test to find out whether the difference between the observed and expected data is due to chance or a real effect
What are the criteria for the chi-squared test?
- Data placed in discrete categories
- Large sample size
- Only raw count data allowed
- No data values equal 0
How can we use a chi-squared test in relation to inheritance?
We can compare expected phenotypic ratios with observed ratios to test our understanding of how different genes and alleles are inherited
What do you conclude when your x^2 value is larger than or equal to the critical value?
There is a significant difference between the observed and expected result (something else other than chance is causing the difference) and the null hypothesis can be rejected
What do you conclude when your x^2 value is smaller than the critical value?
There is no significant difference between the observed and expected results so the null hypothesis can’t be rejected
Define species
A group of organisms that can interbreed to produce fertile offspring
Define a population
All the organisms of a particular species that live in the same place and can potentially interbeed
Define gene pool
The range of different alleles existing for a particlar locus within a population
Define allele frequency
The proportion of a certain allele within a gene pool
What is the Hardy-Weinberg principle
Allows us to estimate the frequency of alleles in a population, as well as if allele frequeency is changing over time
What does the Hardy-Weinberg principle predict
Predicts that the frequencies of alleles in a population won’t change from one generation to the next
Under what conditions is the Hardy-Weinberg principle true?
- No mutations occur to create new alleles
- No migration in/out of the population
- No selection, so alleles are all equally passed on to the next generation
- Random mating
- Large population
Explain the Hardy-Weinberg equation for calculating allele frequency
- The frequencies of each allele for a characteristic must add to 1.0
- The equation: p + q = 1
- Where p = frequency of dominant allele
- Where q = frequency of recessive allele
Explain the Hardy-Weinberg equation for calculating genotype frequency
- Frequencies of each genotype for a characteristic must add to 1.0
- p^2 + 2pq + q^2 = 1
- Where p^2 = frequency of homozygous dominant
- 2pq = frequency of heterozygous
- q^2 = frequency of homozygous recessive
