Download Topic 10 Genetics and Evolution

Topic 10 Genetics and Evolution
10.1 Meiosis
• Chromosomes replicate during s-phase of
interphase.
• During Prophase I, crossing over can occur
between chromatids of homologous
chromosomes.
• New Vocab. The pair of homologous
chromosomes, once they are together they are
called a bivalent
• The actual spot where they touch is called the
chiasma, there can be more than one
• Homologous chromosomes separate during
meiosis anaphase I, sister chromatids separate
during meiosis anaphase II
• Independent assortment during metaphase
says that each allele can separate independent
of the other based on how they line up.
• During metaphase there are 223 ways the
chromosomes can line up, not counting
crossing over.
10.2 Inheritance
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Dihybrid crosses
Two traits
FOIL method
RrYy = RY, Ry, rY, ry
Autosomes & Sex chromosomes
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22 pairs of autosomes
2 sex chromosomes
Autosomal traits have genes on autosome
Sex linked trait has genes on sex
chromosomes.
Linkage groups
• Genes that are on the some chromosome are
usually inherited together. Said to be linked.
• In fruit flies, genes for body color and wing
length are on the same chromosome.
• G=grey
• g=black
• L=long wing
• l=short wing
• If the g’s and the l’s are on the same
chromosome, you don’t give a genotype like
this GgLl, you have to show that they are
linked by doing this….G
L
g
l
So where the G goes, the L goes with it.
You cant foil this like normal
Polygenic Inheritance
• More than one gene influencing the trait, not
multiple alleles, multiple genes.
• It is believed that most traits are polygenic.
• Causes a spectrum of traits called Continuous
variation. Skin color and height are examples.
• Discontinuous variation is from one gene,
blue-brown, disease or no disease, etc
• Continuous traits create a bell curve
10.3 Gene pools and speciation
• Gene pool is all the genetic information in a
certain population at a given time.
• Large gene pools create large variation
• Small gene pools create small variation
• Allele frequency measures the proportion of a
specific allele in a population.
• Does not mean what % of the population have
the allele.
Evolution and allele frequency
• Frequency of alleles changes over time as
good one increase and bad ones decrease.
• Also, populations mixing can change allele
frequency.
• If allele frequency is changing, evolution is
occurring, if it is not changing, evolution is not
happening.
Hardy-Weinberg equation
• Used to calculate the frequency of alleles.
• Can be used to determine how fast a
population is changing.
• p=frequency of dominant allele
• q=frequency of recessive allele
• p + q =1
• P2 + 2pq + q2 = 1
• p2 = frequency of homozygous dominant
• q2 = frequency of homozygous recessive
• 2pq = frequency of heterozygous
Reproductive Isolation
• Something separates a population (gene pool)
• Geographical isolation-land, water etc
• Temporal isolation – time. Example is flowers
reaching maturity at different times.
• Behavioral isolation – lifestyle, habits,
courtship dance.
Directional, stabilizing and disruptive
selection
• Directional selection – when a certain
phenotype is favored over another. Causes
the phenotype to increase in frequency.
Occurs when the environment changes.
• Stabilizing selection is when a phenotype that
is different than both options is favored.
Flower nectar. Move towards the mean
• Disruptive selection – two different extremes
are both favored. Move away from the mean
Polyploidy
• Sex cells have one set of chromosomes (n)
Haploid
• Somatic cells have two sets of chromosomes
(2n). Diploid
• Polyploidy is three or more sets of
chromosomes. (3n), (4n) etc
• More common in plants than animals.
• More vigorous plant, larger fruit, resistant to
disease
Polyploidy
• Can create more replication errors, causes
differences in how they evolve.
• The process of a population changing enough
to be unable to reproduce is called speciation.
Speciation due to divergence
• Two main views as to rate of evolution.
• Small, continuous, slow (gradualism)
• Quick then long periods of time with little or no
change. (punctuated equilibrium)
• Gradualism – Darwin
• Punctuated equilibrium – more recent, due to
sudden environmental change.
• Some species go for millions of years with little or
no change. Sharks, cockroaches, horseshoe crabs
• Incompleteness of fossil record makes it difficult