chapter 20 - patterns of inheritance Flashcards
What is a diploid?
- an organism with a pair of homologous chromosomes, it has 2 alleles of each gene
What is a gene?
- a sequence of dna that codes for a protein
What is a allele?
- A variation of a gene
What is a genotype?
- the combination of alleles that an organism has
What is a phenotype?
- the physical expression of the genotype and its interaction with the enviornment (skin colour)
What is a dominant allele?
- Its an allele that is always expressed in the phenotype
What is a recessive allele?
- alleles that are only expressed when homozygous
What are codominant alleles?
- both alleles are expressed in the phenotype, phenotype is intermediate for both alleles
What is meant by homozygous?
- When both alleles are the same
What is meant by heterozygous?
- when both alleles are not the same
What is the locus?
- the location of a gene on a chromosome
- alleles of the same genes always have the same locus
What is monohybrid inheritance?
- inheritance of a characteristic controlled by a single gene
What is dihybrid inheritance?
- inheritance of two characteristics controlled by two separate genes
What are the phenotypic ratios for both monohybrid and dihybrid inheritance?
- monohybrid - 3:1
- dihybrid - 9:3:3:1
How do the gametes differ in codominance compared to both monohybrid and dihybrid inheritance?
- the gametes are heterozygous whereas in monohybrid and dihybrid the gametes are homozygous
What is an autosome?
- all the non sex chromosomes
what is autosomal linkage?
- its where genes that are on the same autosome are linked
- they will stay together during independant assortment and will be inherited together
- affects the typical phenotypic ratio(9:3:3:1)
- because linked genes are inherited together they behave more like monohybrid cross (3:1)
- autosomal linkage means that more offspring will have the same genotype and phenotype as their parents
What may cause the offspring to not have the same genotype and phenotype?
- the alleles are separated during crossing over
What makes genes more closely related?
- the closer their loci of genes on an autosome, the more closely linked they are
What is a homologous pair?
- same genes
- different alleles
What is sex linkage?
- the expression of alleles located on sex chromosomes depends on the sex of the individual
What type of chromosomes do females and males have and what is the difference between them?
- females have XX chromosomes
- males have XY chromosomes
- the Y chromosome is smaller than X and is missing more genes present on X
What is required in the chromosomes of males and females for them to have haemophilia?
- females, must be homozygous recessive to be a sufferer
- males, the one X chromosome they have must be the faulty allele to be a sufferer
What is epistasis and when does it happen?
- its an interaction between genes . . . when the expression of one gene surpresses the expression of another gene
- it happens when a phenotype is controlled by more than one gene
What affect does epistasis have on dihybrid crosses?
- it changes the typical phenotypic ratio (9:3:3:1)
- if recessive epistatic alleles(9:3:4)
- if dominant epistatic alleles(12:3:1)
What changes the normal phenotypic ratios
- autosomal linkage
- sex linkage
- epistasis
What is genetic bottleneck effect?
Is it in the same geographical location or not?
- we start with a ancestral population
- theres a big decrease in the population this could be due to hunting
- happens in the same geographical location
What does the genetic bottleneck effect result in?
- few individuals survive
- decrease in genetic diversity, meaning fewer alleles in surviving population
- inbreeding
- genetic drift has a greater effect on smaller populations
What is founder effect?
Is it in the same geographical location or not?
- where a few organisms in a population become separated and create a new colony
- this can happen because the organisms get lost or environmental factors prevent them from staying within their population
- it happens in different geographical locations
What does the founder effect result in ?
- new colony formed by a small number of individuals
- genetic diversity decreased
- inbreeding
- genetic drift has a greater effect on smaller populations
- founders have few alleles
What is genetic drift?
- changes in allele frequency between generations due to random chance (e.g random fertilisation)
What is meant by random fertilisation?
- the allele passed to the zygote is random
What is a species?
- organisms that can reproduce to produce fertile offspring
What is a gene pool?
- all the alleles present in a population
What is the difference between a population and a community?
- population, all the organisms of a single species in one place at a time
- community, all the organisms of all the species in one place at one time
What is allele frequency?
- how common an allele is in the population
what is evolution with regards to this topic?
- a change in allele frequency overtime
What is meant by differential reproductive success?
- organisms with a phenotype better adapted to their enviornment have selective advantage and are more likely to survive and reproduce
what is speciation?
- the process of forming a new species
What is the hardy weinberg principle?
- a model that predicts the frequency of alleles, genotypes and phenotypes in a population
What does the hard weinberg principle predict?
- the frequency of alleles of a gene will stay constant over generations
What are assumptions does the hardy weinberg principle assume?
- no mutations
- no selection
- random mating
- large population(no genetic drift )
- no migration
When does speciation occur?
- it happens when populations become reproductively isolated(no gene flow between them)
What are the two types of speciation and what is the difference?
- allopatric speciation, geographical isolation leading to reproductive isolation
- sympatric isolation, non geographical isolation leading to reproductive isolation
What are some examples of sympatric speciation and allopatric speciation?
- allopatric speciation, a river could separate two populations and so that isolates reproduction
- sympatric speciation, examples include:
- seasonal, reproductively active at different times of the year
- behavioural, different courtship behaviour
- hybrid sterility, hybrids of two parents are infertile
- morphological, different shaped genatlia
What does speciation result in?
- variation exists in the population(s) due to mutations
- causes a change in allele frequency
- occurs over many generations(dodo)
- directional reproductive success
- different selection pressures and so directional selection of different phenotypes
What is artificial selection?
- when humans interbreed organisms with useful traits(phenotype) to improve their usefulness
What are some examples of artificial selection?
- dairy cows
- corn
- pedigree dogs
Explain how artificial selection is used in cows?
- a female with a desired trait is selected(high milk yield, high quality, disease resistant)
- select a male with a mother with desired trait
- cross breed them
- select the offspring with the highest trait
-repeat the process over many generations
Explain how artificial selection is used in corn?
- select plants with desirable trait (large ears of grain)
- cross breed them
- select offspring with the best desirable trait
- repeat over many generations
What are the advantages of artificial selection?
- increase in frequency of desirable traits
- bigger/amplified traits
- more efficient farming
What are the disadvantages of artificial selection?
- reduced genetic diversity
- increased expression of genetic disorders, as inbreeding results in the expression of recessive alleles
- ethical issues, pugs can breathe properly
