Chapters 3, 5, & 10 Flashcards
(51 cards)
Outline similarities b/w meiosis I & meiosis II.
- reductive division of chromosomes to produce haploid nuclei
- 4 main stages of meiosis
- division of nucleus & cytoplasm
- nondisjunction occurs in both meiosis I & II
Outline differences b/w meiosis I & meiosis II.
- meiosis I involves interphase before prophase but meiosis II does not
- meiosis I produces 2 haploid cells while meiosis II produced 4 haploid cells
- chromosomes at end of telophase in meiosis I contain 2 sister chromatids, while chromosomes at end of meiosis II contain only 1 chromatid
- in meiosis I, whole chromosomes move to opposite poles of cell while in meiosis II, chromatids move to opposite poles of cell
- chromosome number is HALVED in meiosis I, while chromosome number remains the SAME in meiosis II
- crossing over takes place in meiosis I but not in meiosis II
Outline causes of variation in organisms
- crossing over in meiosis
- random orientation
- fertilisation
- mutations
Law of Independent assortment
independent assortment of genes is due to the random orientation of pairs of homologous chromosomes in meiosis I
dihybrid crosses
crosses in which the parents differ in 2 characteristics that are controlled by 2 different genes
Define genotypic ratio
proportions of the various phenotypes produced by the crosses
Define epistasis
interaction b/w genes –> the expression of 1 gene is modified by the expression of 1 or more other genes
Define speciation
the process by which one group of species diverges into 2 or more species
State 3 types of reproductive isolation
temporal, behavioural, georaphic
Define gene pool
consists of all the genes & their different alleles present in an interbreeding population
What is behavioural isolation?
involves differences in courtship / mating behaviours
What is allopatric (geographic) isolation?
physical barriers exist bw two population
State one factor that can lead to reproductive isolation
polyploidy
Define sympatric speciation.
when there are no physical barriers preventing any members of a species from mating with another, and all members are in close proximity to one another
more common in plants –> polyploidy
Define stabilising selection
favours average phenotype
Define directional selection
when one extreme of the trait is favoured
Define disruptive selection
favouring both extreme phenotypes / the intermediate phenotype has LOWER REPRODUCTIVE FITNESS
Evidence for evolution
- fossils –> show how different species existed in the past / changed over time
- selective breeding –> of domesticated (animal/crop plants) shows that artificial selection can cause rapid change
- homologous (anatomical structures) show common ancestry
- DNA/base/amino acid sequences show how species diverged
How does selective breeding provide evidence for evolution?
- crop plants / domesticated animals produced by selective breeding
- e.g. dogs developed from wolves
- artificial selecting to eliminate undesirable varieties
- selective breeding can cause significant rapid change over time from the original wild species
- changes due to selective breeding shows natural selection can cause change/evolution in species
How do homologous structures provide evidence for evolution?
- similar structure, different function
- pentadactyl limn w/ 5 digits
- adaptive radiation
- e.g. human hands used for tool manipulation, while bird/bat wings used for flying
Key features of natural selection
- overproduction of offspring
- natural variations b/w individuals
- some are better adapted
- better adapted = survival, reproduction
- passing on characteristics to offspring
- frequency of favourable alleles increases in gene pool
- speciation
Define clade
a group of organisms that evolved from a common ancestor
Define cladogram
tree diagrams that show the most probable sequence of divergence in clades
What is allele frequency?
the number of the allele in a population divided by the total number of alleles of the gene
