6.1.2 Genetic inheritance Flashcards
monogenic definition
determined by a single gene
gene locus definition
position of gene on a chromosome
heterozygous definition
having different alleles for the same gene locus on a pair of homologous chromosome
homozygous definition
having same alleles at the same gene locus on a pair of homologous chromosomes
true-bred definition
homozygous
dominant definition
masks the effects of recessive alleles
recessive definition
masked by dominant alleles
F1 definition
first generation of offspring (to original parents)
F2 definition
second generation (offspring of F1)
continuous variation features
no defined categories
there is a range (any value is possible)
caused by more than one gene and often environment
greater number of gene loci contributing to characteristic, greater range in variation
quantitative
discontinuous variation features
discrete categories with no intermediates
usually caused by one gene
genes at different loci may interact to influence one characteristic and cause discontinuous variation
no/very little environmental effects cause it
qualitative
polygenic definition
caused by more than one gene
epistasis definition
expression of one gene is affected by expression of one or more independently inherited genes
environmental factors that influence variation
diet in animals leads to changes in mass (malnutrition)
language
scars
plants grown in too little light experience etiolation (rapidly growing stems, weakened cell walls, chlorosis)
chlorosis definition
lack of chlorophyll
the environmental factors prevent the expression of genes for chlorophyll production
different blood groups phenotypes
A
B
AB
O
sex linkage definition
when a gene is present on one of the sex chromosomes
why sex chromosomes are not fully homologous and its impact
Y chromosome lacks many genes that code for characteristics on X chromosome
men can neither be homozygous nor heterozygous for these genes
men more likely to have genetic diseases linked to genes on these chromosomes
Haemophilia in genes
found on X chromosome but not Y
functional:faulty allele = X^H:X^h
colour blindess
gene causing red-green colour blindness
found on X but not on Y chromosomes
functional/faulty allele: X^B/X^b
autosome definition
non-sex genes
autosomal linkage definition
linkage when 2 or more genes on the same chromosome are inherited together (they dont undergo independent assortment in metaphase 1)
epistasis definition
interaction of non-linked genes (on different chromosomes) where one masks the expression of the other
epistasis effect on number of phenotypes
epistasis reduces number of phenotypes in F2 generation and reduced variation
epistatic alleles definition
alleles masking the effect of the alleles on the other gene
hypostatic alleles definition
alleles whose effect is being masked
recessive epistasis definition
when homozygous recessive alleles of gene locus 1 are epistatic to both alleles on gene locus 2 (hypostatic)
9:3:4 ratio
dominant epistasis definition
where dominant alleles of gene locus 1 are epistatic to both alleles on gene locus 2 (hypostatic)
12:3:1 or 13:3 ratio
epistasis by complementary gene action definition
when 2 different genes work together to express phenotypes
9:7 or 9:3:4 phenotypic ratio
what a non 9:3:3:1 phenotypic ratio means for 4 phenotypes for 2 genes/traits
autosomal linked and crossing over will have occurred
further apart the gene loci for linked genes, the more likely crossing over is and higher the number of recombinant phenotypes
natural selection/evolution method
V: individuals of a population of same species have different characteristics due to genetic variation
O: overproduction of offspring
S: selection pressure kills individuals with less advantageous characteristics die
S: those with more advantageous characteristics survive
AR: those who survive are more likely to reproduce and advantageous alleles are passed onto their offspring
Hardy Weinberg assumptions
large population no genetic drift random mating no natural selection no mutation no migration
2 types of natural selection
stabilising selection
directional selection
stabilising selection features
occurs when organisms’ environment doesn’t change
favours intermediate phenotype (over extremes)
reduces variation in a population (e.g. those with short/long fur in constant temperatures selected against, mid length fur will survive, higher frequency of alleles for mid length fur)
directional selection features
occurs when environment changes favours new (extreme) phenotype causes change in population’s mean phenotype
genetic drift definition
random changes in alleles frequency in small populations
genetic drift features
only small populations as each individual forms a larger proportion of gene pool and greater effect on gene pool
not due to natural selection, chance only
population alleles can drift from original, could lose alleles from gene pool
2 types of genetic drift
genetic bottleneck
founder effect
genetic bottleneck features
an event reduces numbers of a population
some alleles lost from population at random
genetic variation reduced -> genetic drift
founder effect features
small number of individuals from an original larger population
establish a new population
some alleles lost from population at random (these could be advantageous)
genetic variation reduced -> genetic drift
speciation definition
splitting of a population of a species into 2 isolated population that overtime undergo genetic changes, resulting in reproductive isolation and the formation of 2 different species
allopatric speciation mechanism
populations are physically separated e.g. by water/mountains/fences
barrier prevents gene flow between populations
genetic changes occur in species (caused by genetic drift, mutations or natural selection (different pressures in different areas))
populations become so genetically different they can no longer interbreed (reproductively isolated)
new species has been formed
sympathetic speciation mechanism
several things can lead to individuals in a population become reproductively isolated:
• behavioural changes (sleep patterns, courtship behaviours)
• biological changes (size differences, genitalia differences)
• genetic changes (change in chromosome number, prevents zygote viability)
populations can no longer interbreed to produce fertile offspring, new species been formed
artificial selection definition
selective breeding of organisms in order to produce desired phenotypes in an organism (often to benefit to humans)
humans choose parents with desired phenotypes and therefore desired alleles and interbreed them to produce offspring with higher frequency of these phenotypes, repeated over many generatjons
stages of artificial selection
male and female with desired characteristic chosen and bred together
some of the offspring will carry all of the desired characteristics of the mother and father
choose the offspring with the all of the desired characteristics and breed together
repeat
inbreeding features
genetic diversity decreases with each generation, individuals become more and more related
likelihood of unintentionally selecting 2 copies of a harmful recessive allele increases in small gene loci
…
hybrid vigour definition
outcross individuals belonging to 2 different varieties to obtain individuals heterozygous at many gene loci
how/when gene has multiple alleles
when it has 3 or more alleles
