Study Guides (380,000)
CA (150,000)
UTSC (10,000)

BIOB11H3 Study Guide - Zygote, Wild Type, Chromatin


Department
Biological Sciences
Course Code
BIOB11H3
Professor
Dan Riggs

This preview shows pages 1-3. to view the full 10 pages of the document.
Cell Biology Lecture 1 Paraniya Balakumar
1
In the year 2013: many genomes completely sequenced “Bioinformaticscomes of age
Most organisms are diploid: two copies of each gene
An allele is an alternative form of the same gene
A genotype is the genetic composition of the organism
A phenotype is the observable traits that an organism exhibits or the morphology
Some traits that Gregor Mendol used to establish basis of heredity were to use the genes of tall pea
plants VS. short pea plants
He decided to measure his pea plants and disocovered that some of his pea plants were
tall and some were short in term of height, tall seems to be dominant trait over short, yellow
vs. green, and round vs. wrinkled
The idea here is to understand that for every trait there are at least two forms one of them
being dominant to the other one
He followed particular traits by conducting crosses
When one conducts a cross a sperm and egg get together; easy in plants as many are self fertile
and will do the work by itself
Punnett square gives you a possible of outcome of what you will see when one crosses
Organisms are diploid let’s look at the contribution of a sperm and the contribution of the
egg for one particular gene that being a round vs wrinkled phenotype
o If the sperm is carrying either of those two; you use the sperm to fertilize eggs what
will happen?
Sperm donates large R and egg donates a large R = progeny is going to
round
Only time you will get a wrinkled plant is when you get a small r from the
sperm and a small r from the sperm producing a recessive gene rr
o Self crossing of Rr (heterozygous) plant produced a 3:1 ratio of round:
wrinkled; you will have round producing plants vs. one wrinkled
Homozygous means that both alleles are identical (ex.dominant, recessive). If dominant,
generally the “wildtype” (RR)
Heterozygous means that both alleles differ from one another (one dominant, one
recessive (Rr)
Nulls means homozygous recessive (rr). It is generally associated with the “mutant” trait. ¼
possibility to get this , and is not found as often
4
R (round)
r (wrinkled)
R (round) r (wrinkled)
Sperm
RR Rr
Rr rr
round round
round wrinkled
Mendel: Following the round vs wrinkled seed phenotype
Conduct a cross: sperm and eggs get together; easy in plants
as many are self fertile and will do the work for you.
Phenotype: observable traits or morphology
Self crossing of Rr plant produced 3:1 ratio of round:wrinkled
Punnett Square
To understand Mendels laws-some vocabulary words:
Homozygous: both alleles are identical (e.g. dominant)
Heterozygous: alleles differ (one dominant, one
recessive)= Rr
Nulls: homozygous recessive (rr)
Generally associated with the mutant trait
If dominant, generally the ‘wildtype’ (RR)
Transcription, translation
Active protein or enzyme
Transcription, translation
Inactive protein or enzyme
Mutation that
alters genetic
code
Heterozygote example: Mother donates normal gene; father
donates mutant gene: heterozygous progeny often exhibits normal
activity
DOMINANT allele
RECESSIVE allele
Example of mutation: Wrinkled peas
Recessive allele=wrinkled
Known to be due to mutation in a gene
encoding a starch branching enzyme
Seed doesnt fill properly and thus appears shrunken or
wrinkled.
R
Insertion of 800bp disrupts gene
r

Only pages 1-3 are available for preview. Some parts have been intentionally blurred.

2
In the case of a heterozygote example in which a mother donates normal gene; and the father
donates a mutant gene: heterozygous progeny often exhibits “normal” activity
Offspring usually exhibit the normal phenotype presence of the dominant gene
Red shows the father chromosome that has the mutation in the gene (recessive) that
mutation somehow alters the genetic code and so that’s not so good
Orange shows the mother chromosome that was donated shows the dominant allele and
can see that when transcription and translation takes place an active protein or enzyme is
produced and so on
The father’s contribution translation and transcription may take place but enzyme may be
produced that doesn’t do that right thing but since the mother has donated the dominant
gene, usually in these situations of heterozygote you have a normal functioning child
As an example there is Mendel’s wrinkled peas; can see in the photograph where there is a peapod
with several wrinkled seeds = due to mutation (insertion into the gene of about 800 base pairs of this
foreign DNA sequence)
What happens for these wrinkled seeds is that the seed doesn’t fill properly and thus
appears shrunken or wrinkled
o Starch branching does not occur since there is a insertion of the 800 base pair which
in turn disrupts the gene
Mendels Laws include the law of segregation and the law of independent assortment
Law of Segregation is when two alleles of a gene segregate from one another into the
gametes. Thus, half of the gametes carry one of the alleles and the other half of the
gametes carry the second allele
o Key is to understand that alleles refer to one gene
o Inheritance of the distribution of the alleles of one gene
Law of Independent Assortment is when different genes assort independently during
gamete formation. That is, the gene for seed color segregates independently from the
gene for seed shape.
o Key is to understand that two genes are considered
4
R (round)
r (wrinkled)
R (round) r (wrinkled)
Sperm
RR Rr
Rr rr
round round
round wrinkled
Mendel: Following the round vs wrinkled seed phenotype
Conduct a cross: sperm and eggs get together; easy in plants
as many are self fertile and will do the work for you.
Phenotype: observable traits or morphology
Self crossing of Rr plant produced 3:1 ratio of round:wrinkled
Punnett Square
To understand Mendels laws-some vocabulary words:
Homozygous: both alleles are identical (e.g. dominant)
Heterozygous: alleles differ (one dominant, one
recessive)= Rr
Nulls: homozygous recessive (rr)
Generally associated with the mutant trait
If dominant, generally the ‘wildtype’ (RR)
Transcription, translation
Active protein or enzyme
Transcription, translation
Inactive protein or enzyme
Mutation that
alters genetic
code
Heterozygote example: Mother donates normal gene; father
donates mutant gene: heterozygous progeny often exhibits normal
activity
DOMINANT allele
RECESSIVE allele
Example of mutation: Wrinkled peas
Recessive allele=wrinkled
Known to be due to mutation in a gene
encoding a starch branching enzyme
Seed doesnt fill properly and thus appears shrunken or
wrinkled.
R
Insertion of 800bp disrupts gene
r

Only pages 1-3 are available for preview. Some parts have been intentionally blurred.

3
Diploid of course means that there are two copies of each gene and heredity is basically based on
two things:
a. Sex
b. What happens during genesis (different outcome every time)
Why do we get a different outcome each time? Sources of variation include:
1. Meiosis which is a reductional division in which haploid sperm and haploid eggs are produced
(only donating one or the other two possibility in each sperm or egg)
2. Recombination occurs between maternal and paternal chromosomes to give unique genetic
information
3. Specific combinations of a recombinant sperm and egg produces a genetically unique individual
2N cell (diploid) recombination 1st division (Homologs disjoin)
4N cell 2 x 2N cells 2nd division (Sister chromatids disjoin) 2N cell 2 x 1N cells
MITOSIS
One diploid "parent" cell divides to produce two genetically identical "daughter" cells.
This type of cell division is used for
asexual reproduction in unicellular organisms
o Even some multicellular species reproduce via PARTHENOGENESIS ("virgin birth").
o a CLONE is a group of genetically identical organisms produced via asexual means.
(It is not an individual organism produced via cloning.)
o In times of stress, even species that ordinarily reproduce asexually may revert to
sexual reproduction. Why might this be an advantage to the organism?
somatic (body) growth in multicellular organisms
it occurs throughout the body, wherever there is growth
MEIOSIS
One diploid "parent" cell divides to produce four genetically unique "daughter" cells which will then be
processed into gametes (the sex cells we usually know as "ova" and "sperm")
This type of cell division is used for
sexual reproduction
it requires the halving of the genetic material (DNA) in preparation for recombination with
an equal amount of DNA from the same species
it (usually) occurs in specialized regions of the body known as gonads
o ovaries (female) and testes (male) in animals
o archegonia (female) and antheridia (male) in plants
Sexual reproduction requires meiosis, a process in which a parent cell divides to produce cells
with half the genetic material of the parent.
A diploid parent cell, for example, divides to make four haploid cells. In sexual reproduction,
haploid gametes from two individuals then combine to produce a diploid zygote. An
offspring resulting from sexual reproduction is genetically different from both parents
Meiosis consists of 4 stages and two cell divisions : prophase, metaphase, anaphase, and
telophase
Before meiosis begins, in the preceding interphase, DNA replication takes place. At this
point, the chromosomes are not visible under a light microscope.
You're Reading a Preview

Unlock to view full version