Chapter 18:Regulation of Gene Expression

• • One main circularchromosome
• • DNA is usually naked
• • Compact genome - mostDNA is coding (genes)
• • Always HAPLOID
• • Reproduce by binary fission(asexual) producing clones– Genetic variation comes frommechanisms that are NOT associatedwith reproduction

Many linear circular chromosomes

DNA is wrapped around proteins called histones(chromatin)

Large genomes-­‐less than 3% of DNA codes for genes

Haploid or diploid

Animals and higher plants are mostly diploid

In higher plants and animals, reproduction is usually connected with genetic recombination

• 1.)   
• Mendel didn’t know
• about Meiosis, but we do now. State and explain both of Mendel’s laws and
• identify the event of meiosis that is responsible for each of them. Be sure to
• mention which phase of meiosis these events occur in..

 

• The law of
• segregation states that each organism has two alleles for each gene. They
• separate from each other during meiosis I in anaphase.

• Independent
• Assortment is when the genes of multiple traits segregate independently when
• gametes are formed during anaphase II. Each cell receives half of the normal
• amount of chromosomes.

• Dominance depends
• if a chromosome inherits a certain allele. This occurs during crossing over of
• genetic material in prophase I

 

• 2.)   
• Mendel’s laws can
• explain the inheritance of many characteristics and combinations of traits. For
• some other situations, however, the story is more complicated. Give and explain
• three different situations when certain traits or combinations of traits that
• are inherited in more complicated ways than what Mendel’s laws would predict.
• (These must be three separate reasons, not just three different examples of the
• same phenomenon.

 

• Incomplete Dominance is when neither
• trait is completely dominant to each other. An example is when a red flower and
• a white flower breed and the genes for red pigments are not dominant or
• recessive. It has a few pigments of red but not enough for a pure color. The
• offspring may have a pink color.

 

• Overdominance is when a heterozygote can
• express a phenotype more extreme than the parent generation.  In tomatoes the wild-type genes evenly
• express fruit and plant growth. The mutant allele produced more leaves. When
• mixed in a heterozygous offspring the result is much more fruit which is
• preferable to humans.

 

• Codominance happens
• when two or more alleles influence the phenotype of an organism. An example is
• human blood types. Blood type 0 codes for no antigen however blood types A and
• B codes for each antigen. A and B are neither recessive or dominant to each
• other so both can exist in a person’s body giving us Blood type AB.

 

• 3.)   
• Describe what
• happens to the DNA of A human somatic cell throughout the course of one
• complete cell cycle. Tell this like a story where you are a reporter “watching”
• the DNA. Don’t bother with anything else – just tell the story of the full cell
• division cycle from the point of view of DNA.

 

• The DNA
• spends most of its time being read like a most to create RNA strands. In fact
• in certain cells that do not divide DNA will spend all its time in this state.
• In the S phase DNA replicates with each new strand coming together with a
• parent strand in the semi conservative model. 
• During mitosis is where things begin to get more interesting. Prophase
• is where chromosomes condense and the mitotic spindle begins to form centrosome
• pairs separate holding some of the microtubules. IN prometaphase the nuclear
• envelop dissolves exposing the chromosomes and kinetochores are formed for the
• microtubules to grab onto. Metaphase is where chromosomes line up and the
• sister chromatids are opposite each other. They form an imaginary line called
• the metaphase plate down the middle of the cell. During anaphase the sister
• chromatids are pulled apart as the cell elongates. Finally at telophase the
• sisters are fully separated and the nuclear envelope beings to form once more
• of each cell.

 

 

 

• 4.)   
• First, make up two
• traits and two versions of those traits. (For example, you could say height and
• weight and pretend there were only two versions of each – tall/short and
• heavy/light. But think of your own examples!) Secondly, give a short
• explanation, as if to someone with no knowledge of genetics, how They would be
• inherited if they were located close together on the same chromosome. Third,
• explain how it would be different if they were located on different
• chromosomes. Your explanations should include some example scenarios or data.

 

• Genetic
• Recombination  Linkage
• map

• Crossing over occurs in
• Prophase 1 of meiosis