Diversity and Selection (Topic 4B) Flashcards
diploid number in abbreviated to…
2n
how many chromosomes does a diploid cell have?
two of each chromosome - one from each parent
pairs of matching chromosomes are called…
homologous pairs
what type of cell are gametes?
haploid
haploid number is abbreviated to….
n
how many chromosomes does a haploid cell have?
one copy of each chromosome in a homologous pair
what is the haploid number for humans?
23
when gametes fuse during reproduction they form a…
zygote
meiosis starts with _____ cells and produces _____ cells
diploid
haploid
meiosis produces…
gametes
before meiosis can occur what 2 steps have to happen?
DNA unravels and replicates so there are two copies of each chromosome, called chromatids
DNA condenses to form sister chromatids joined by a centromere
what happens in MEIOSIS I?
the chromosomes arrange themselves into homologous pairs that are then seperated, halving the chromosome number
after MEIOSIS I occurs what happens next?
MEIOSIS II
what happens in MEIOSIS II?
the pairs of sister chromatids are seperated. 4 genetically different haploid cells are produced
what two events occur during meiosis that lead to genetic variation?
- crossing over of chromatids
- independent segregation of chromosomes
what is crossing over of chromatids?
the chromatids twist around each other and bits of chromatids swap over
what is independent segregation of chromosomes?
homologous pairs are separated at random in MEIOSIS I so the daughter cells produced have completely different maternal and paternal combinations of chromosomes
what is a substitution mutation?
one base is substituted with another
what is a deletion mutation?
one base is deleted
the order of DNA bases in a gene determines the…
order of amino acids in a protein
why won’t all substitution mutations end up causing a change in the amino acid sequence?
genetic code is degenerate so some amino acids are coded for by more than one triplet so the same amino acid may be expressed still
why will a base deletion always cause a different amino acid to be produced?
a deletion changes the number of bases present which causes a shift in all base triplets after it
what are mutagenic agents?
something that increases the probability of a mutation occuring
what is chromosome disjunction?
a chromosome mutation where the chromosomes fail to separate properly
genetic diversity is…
the number of different alleles of genes in a species or population
genetic diversity in a population is increased by…
- mutations in DNA forming new alleles
- gene flow
gene flow is….
caused by…
when different alleles are introduced into a population
caused by individuals from another population migrate into it and reproduce
a genetic bottleneck is…
an event which causes a big reduction in population
what effect does a genetic bottleneck have on a population?
reduces the number of different alleles in the gene pool, reducing genetic diversity
describe the process of natural selection
- in a population some individuals have an advantageous allele that increases their chance of survival so are more likely to survive and reproduce, passing on the allele
- so a greater proportion of the next generation have this allele
- they in turn are more likely to survive and pass on the allele
- frequency of the allele in the population increases each generation
- this leads to evolution as the allele becomes more common in the population
what are the three types of adaption an animal can do to increase its chance of survival?
behavioral
physiological
anatomical
what is a behavioral adaption?
the way an organism acts that increases its chance of survival
what is a physiological adaption?
processes inside the organisms body which increase their chance of survival
what is an anatomical adaption?
structural features of an organisms body that increases its chance of survival
directional selection works against ___ of the _____ in a range of ____
one
extremes
phenotypes
directional selection results in…
one phenotype becoming rare and another becoming common
stabilising selection works against ___ _____ in a range of ____
both extremes in a range of phenotypes
stabilising selection results in…
variation about the mode being reduced
disruptive selection is when…
extremes at both ends of the phenotype are favoured
disruptive selection results in…
two or more different species forming
what is an inhibition zone?
a patch where bacteria cannot grow on the agar
the size of an inhibition zone tells you…
how well an antibiotic works
