6.2 patterns of inheritance Flashcards
define genotype and phenotype
genotype = genetic makeup of an organism
phenotype = visible characteristics of an organism
name the genetic factors that lead to phenotype variation
gene mutations
chromosome mutations
sexual reproduction
define polyploidy
more then two sets of chromosomes
define aneuploidy
chromosome number is not an exact multiple of the haploid number
when chromosomes/ chromatids fail to seperate
explain what non disjunction is
one pair of chromosomes or chromatids fails to seperate leaving one gamete with an extra chromosome
explain how sexual reproduction causes genetic variation
random fertilisation
crossing over
independent assortment in metaphase/ anaphase 1 and 2
explain what etoilation in plants
plants grow long and spindly due to trying to find light
explain how environmental factors causes variation
eg. dialect, losing a limb
environment can interact with genes
define allele
different versions of a gene
define homozygous
having identical alleles at a gene locus on a pair of homologous chromosomes
define heterozygous
having different alleles at a particular gene locus on a pair of homologous chromosomes
define monogenic
determined by a single gene
explain what monogenic inheritance is
inheriting one allele from each parent of a particular gene
dominant and recessive alleles
phenotype can be predicted through a test cross/ punnett square
ratio for monogenic heterozygous parents
3:1
define dihybrid
involves two gene loci
explain what dihybrid inheritance is
inheriting alleles for two different characteristics
ratio for heterozygous dihybrid cross
9:3:3:1
define multiple alleles
characteristic for which there are 3 or more alleles in a populations gene pool
example of inheritance of multiple alleles
human blood group
rabbit coat colours
define codominance
both alleles inherited are expressed
results in different phenotypes
ratio for codominance heterozygous parents
1:2:1
explain what codominance is
you inherit two alleles for a particular gene
need two for the phenotype to be displayed
define sex linked
gene present on one of the sex chromosomes (the 23rd pair)
sex chromosomes for males and females
males = XY
females = XX
why are males more likely to suffer from genetic disease
males only have XY so disease carried on the X allele is the only version
females are likely to contain s functioning allele on the other X
males are haploid for X linked genes so cannot be hetero or homo. for X linked genes (only get one)
what are humans sex linked for
haemophilia A
colour blindness
define autosomal linkage
gene loci that is present on the same autosome (not sex linked) that are inherited together
what is autosomal inheritance
genes inherited on autosomes/ not sex chromosomes
define epistasis
the interaction of other genes when one gene masks or supresses the expression of another
recessive epistasis
two recessive alleles at one locus masks the expression of alleles at the second locus
ratio for recessive epistasis
9:4:3
dominant epistasis
a dominant allele at one of the gene locus will mask the expression of alleles at the second locus
ratio of dominant epistasis of heterozygous parents
12:3:1 or 13:1
complimentary epistasis
the presence of a particular allele at each locus is required for the expression of a particular phenotype
purpose of chi squared
find out if difference between observed and expected data is significant or due to chance
define continuous variation
genetic variation in a population shows a range with a smooth gradient between the intermediates
define discontinuous variation
when phenotype classes are distinct and discrete, no intermediates between
what determines continuous and discontinuous variation
continuous = many genes and environment
discontinuous = one gene
define population
members of a species living in the same place at the same time and can successfully interbreed
define natural selection
gradual change in allele frequencies in a population
may lead to the development of a new species
name the types of selection
directional selection
stabilising selection
define stabilising selection
natural selection leading to consistency in a population
define directional selection
natural selection that occurs when an environmental change favours a new phenotype so results in a change in the population mean
explain what genetic drift is
gradual change in allele frequencies down to chance instead of selection pressures
- small populations = less genetic variation = chance can affect allele frequencies drastically = large genetic drift
- large populations = more genetic variation = chance is less likely to impact allele frequencies = less genetic drift
define genetic bottleneck
large reduction in size of a population due to environmental catastrophes = reduces genetic diversity
when population increases again = large reduction in the gene pool
define the founder effect
occurs when a small number of individuals from a large parent population start a new population
will experience a loss of genetic variation
explain what the hardy weinburg principle is
if certain conditions are met then the allele frequencies of a gene within a population will not change from one generation to the next
calculates allele and genotype frequencies within populations
what assumptions need to be met for the hardy weinburg principle
large population
random mating occurs
no migration, mutation, or selection
no selective advantage
What does p, q, p2, q2 stand for
p= frequency of dominant allele
q= frequency of recessive allele
p2 = frequency of phenotype
q2= frequency of genotype
2pq= frequency of heterozygous genotype
Name the two types of isolating mechanisms
Geographical
Reproductive
Define speciation
The splitting of a genetically similar population into two or more populations which revolve into different species
what is needed for speciation to occur
mutation/ genetic diversity
natural/ directional selection
selection pressure is different to other population
time
Explain what geographical isolation is
Populations are separated by geographical features
Acts as a barrier to gene flow between populations
Define allopatric speciation
Formation of two different species from one original species due to geographical isolation
Explain how allopatric speciation occurs/ geographical isolation
Isolated populations experience different selection pressures
Change to allele frequencies due to natural selection/ genetic drift
Each population has now adapted to environment = new species
Explain reproductive isolation
Biological and behavioural changes in a species may lead to reproductive isolation of another population
Seasonal changes - different mating seasons
Mechanical changes - change sun genetilia preventing successful mating
Behavioural changes - different courtship rituals
Define sympatric speciation
Formation of two different species from one original species due to reproductive isolation whilst in the same location
Define artificial selection
Selective breeding of organisms
Define inbreeding depression
When related individuals are crossed inbreeding occurs, more likely to inherit two copies of a harmful allele
Define hybrid vigour
Breeders outcross individuals belonging to two different varieties to obtain individuals that are heterozygous at many gene loci
principles of artificial selection
organism with desirable trait is selected
selectively bred together
individuals are selected by their phenotype not their genotype
artificial selection in cows and plants example
female cow with highest milk yield bred with bull with the highest milk yield
plants bred with the most disease resistance, crop yield, tolerance to weather
ethical issues with artificial selection
lead to inbreeding - reduces gene pool - inbreeding depression
greater chance of organisms inheriting genetic defects, vulnerable to new diseases
ethical issues of artificial selection in dogs
bred to improve species
has created issues - pugs and breathing
