bio exam Flashcards
What is interphase? What main events take place here as the cell is waiting to begin division?
Cell carries out its normal functions, grows, and makes copies of its genetic material in preparation for the next stage of the cycle
Divided into three phases. The length of these phases varies depending on the species and type of cell
G1- cell is getting bigger but will approach maximum size in order to support the transportations of chemicals and proteins, this is when the cell makes proteins needed for replication
is the cell large enough? does it have enough energy?
S- DNA is doubled before entering mitosis where it will be split in half
proper proteins (CDKs) signal division
G2- microtubules are used to move proteins, vesicles, mitochondria, chromosomes, etc. around the cell in preparation for mitosis
has everything been replicated without mistakes or damage?
Distinguish between the different phases of meiosis (including diagrams)
Miosis
- produces 4 cells from one parent cell, and each cell has 23 chromosomes
- requires two parents to produce genetically distinct offspring (exception: identical twins).
- It involves the fusion of a male sperm reproductive cell (sperm) and a female reproductive cell (egg).
- These gametes fuse and become a zygote in a process called fertilization.
- Cells from one parent are referred to as haploids because they contain a single set of chromosomes.
- Once the gametes are fertilized, they become diploid because they now contain a full set of chromosomes from both parents, this is called a zygote.
- haploid gametes are important to keep the chromosome number from doubling in each future generation. they are produced by a process called miosis, which only occurs in the reproductive organs (ovaries and testes)
- In miosis, DNA replicates once but nucleus divides twice
Prophase I
- Chromosomes are formed and condensed and line up beside each other (synapsis)
- Here the homologous chromosomes participate in crossing over where they exchange genetic information
This provides genetic diversity
Metaphase I
- Chromosomes align in pairs at the centre of the cell
Anaphase I
- Chromosome pairs separate to opposite ends of the cell with sister
chromatids remaining together
- Note: a chromosome from the mom went one way, and a chromosome from the dad went another way
- This allows for a mix on either side which is called independent assortment, leading to genetic diversity
- The number of chromosomes is reduced from diploid (2n) to haploid (n)
- The number of genetically distinct gametes that can be produced from a diploid cell is 2n
- n= the number of chromosome pairs
If humans have 23 chromosome pairs, there are 223 (~8 million) genetically distinct gametes that can be produced during meiosis!
Telophase I
- Two daughter cells are formed with
each daughter containing one chromosome of the pair (mom or dad)
- Chromosomes uncoil, spindle fibres disappear, nucleus reforms
- There are now two haploid daughter cells
Meiosis II
- The cells from Meiosis I are haploid as they do not have 2 copies of each chromosome.
- They remain haploid, but further separate to create four gametes
Prophase II
- Unlike Prophase I, crossing over does not occur here
- DNA does not replicate
- Chromosomes condense, and the nucleus disappears
- Centrosomes move to the opposite ends
Metaphase II
- Chromosomes line up at the centre of the cell
- Note: they are no longer in pairs
- Spindle fibres attach to centromeres
Anaphase II
- Spindle fibres pull chromosomes apart
- Sister chromatids move separately to each pole
- Independent assortment occurs again
Telophase II
-Chromosomes unwind
- Nucleus reforms
- Cytokinesis occurs producing 4 haploid daughter cells that are ready for fertilization!
How are haploid gametes created? What is formed through their fertilization?
- Cells from one parent are referred to as haploids because they contain a single set of chromosomes.
- Once the gametes are fertilized, they become diploid because they now contain a full set of chromosomes from both parents, this is called a zygote.
- haploid gametes are important to keep the chromosome number from doubling in each future generation. they are produced by a process called miosis, which only occurs in the reproductive organs (ovaries and testes)
- In miosis, DNA replicates once but nucleus divides twice
- During meiosis I, homologous chromosomes (one from each parent) pair up and exchange genetic material through crossing over. They then separate, resulting in two daughter cells, each with a haploid set of chromosomes.
- In meiosis II, the two daughter cells from meiosis I each divide again, similar to mitosis but without chromosome replication. This results in a total of four haploid gametes, each with a unique combination of genetic material.
- The zygote, formed through the fusion of sperm and egg, is diploid. It contains a complete set of chromosomes (one set from each parent) and has the potential to develop into a new organism through cell division and differentiation.
What is the outcome of mitosis? What is the outcome of meiosis?
Mitosis
Mitosis is a type of cell division that occurs in somatic (non-reproductive) cells. The outcome of mitosis is the formation of two identical daughter cells, each with the same number of chromosomes as the parent cell. The key points about mitosis are:
Purpose: Growth, repair, and maintenance of multicellular organisms.
Number of Divisions: One division.
Number of Daughter Cells: Two.
Genetic Composition of Daughter Cells: Identical to the parent cell and to each other.
Chromosome Number: Diploid (same as the parent cell).
Genetic Recombination: No genetic recombination (except for rare mutation events).
Meiosis
Meiosis is a specialized type of cell division that occurs only in cells destined to become gametes (sperm and egg cells). The outcome of meiosis is the formation of four non-identical daughter cells, each with half the number of chromosomes of the parent cell. The key points about meiosis are:
Purpose: Production of gametes (sperm and egg cells) for sexual reproduction.
Number of Divisions: Two divisions (meiosis I and meiosis II).
Number of Daughter Cells: Four.
Genetic Composition of Daughter Cells: Each daughter cell is genetically unique due to crossing over (genetic recombination) during prophase I of meiosis.
Chromosome Number: Haploid (half the number of chromosomes as the parent cell).
Genetic Recombination: Occurs through crossing over during prophase I, leading to genetic diversity among gametes.
What is nondisjunction? How does this happen? What does it cause?
occurs when homologous chromosomes fail to separate during anaphase I or sister chromatids fail to separate during anaphase II. This can cause an extra chromosome (trisomy) or a missing chromosome (monosomy)
During meiosis I, homologous chromosomes (pairs of chromosomes) should separate, with one member of each pair going to each daughter cell. If nondisjunction occurs during meiosis I, both chromosomes of a homologous pair move to the same daughter cell, resulting in one cell receiving an extra chromosome and the other cell lacking that chromosome.
During meiosis II, sister chromatids should separate, with one chromatid going to each daughter cell. If nondisjunction occurs during meiosis II, both chromatids of a chromosome move to the same daughter cell, resulting in one cell having an extra chromosome and the other cell lacking that chromosome.
can cause Genetic Disorders: Aneuploidy resulting from nondisjunction can lead to genetic disorders and developmental abnormalities in offspring if an aneuploid gamete participates in fertilization.
Example: trisomy 21, which is known as down syndrome, causes facial characteristics, heart defects, susceptible to respiratory disease, Alzheimer’s, and intellectual disability
What are the products of oogenesis? What are the products of spermatogenesis?
oogenesis
- Meiosis takes place in the ovaries
- Begins with a diploid cell called an oogonium
- These cells reproduce by a combination of mitosis and meiosis but stop at Prophase I and wait their turn to continue since only one goes at a time
- Meiosis I only continues for one cell each month beginning at puberty
- When the cell divides it divides unevenly creating one polar body (cannot be fertilized) and one viable egg
- The viable egg will continue through Meiosis I and Meiosis II (pausing at Metaphase II), in preparation for fertilization
- If the viable egg is fertilized by a sperm, the cell can complete Meiosis II, producing a second polar body
- The haploid nucleus of the egg cell then fuses with the haploid nucleus of the sperm cell to complete fertilization and produce a diploid zygote
- production of eggs
Spermatogenesis
- Meiosis takes place in the testes
- Begins with a diploid cell called a spermatogonium
- These cells reproduce by a combination of mitosis and meiosis to create four mature sperm cells
- production of sperm
3 key differences:
(1) In oogenesis cytokinesis is unequal in daughter cells
- Ensures only one zygote forms during fertilization so that nutrients are not divided
(2) At birth the ovary contains all the cells it will ever have that will overtime develop into eggs, whereas sperm continuously
develop throughout the male’s reproductive years
(3) Oogenesis has a long resting period after prophase I until they are activated by hormones to continue the process
What is a nucleotide? How does a DNA and RNA nucleotide differ?
- DNA consists of two molecules that are arranged into a ladder-like spiral shape structure called a double helix
- A molecule of DNA is made up of millions of tiny subunits called nucleotides
- Each nucleotide consists of three things:
(1) Pentose sugar
-5 carbon sugar - DNA has deoxyribose sugar
- RNA has ribose sugar
(2) Phosphate group
-A phosphorus oxygen bond - Important because it links the sugar from one nucleotide to the phosphate of the next to connect many together
(3) Nitrogenous base - There are 4 bases in DNA:
○ Thymine (T)
○ Adenine (A)
○ Cytosine (C)
○ Guanine (G) - There are 4 bases in RNA:
○ Uracil (U)
○ Adenine (A)
○ Cytosine (C)
○ Guanine (G)
complementary base pairs
A pairs with T → forms a base pair with 2 hydrogen bonds
C pairs with G → forms a base pair with 3 hydrogen bonds
Note: in RNA A pairs with U instead of T
Know the difference between the inheritance pattern of autosomal and sex-linked traits
Autosomal Traits:
Autosomal traits are determined by genes located on the autosomes (non-sex chromosomes). Humans have 22 pairs of autosomes and 1 pair of sex chromosomes (XX in females and XY in males). Here are key features of inheritance for autosomal traits:
- Dominant Autosomal Traits:
If an individual inherits at least one copy of the dominant allele (A), they will exhibit the trait.
- Recessive Autosomal Traits:
An individual must inherit two copies of the recessive allele (a) to exhibit the trait.
Inheritance Pattern:
- Autosomal traits follow Mendelian inheritance patterns (e.g., dominant-recessive, co-dominant, etc.).
They can affect both males and females equally because they are not linked to the sex chromosomes.
Sex-linked traits
Sex-linked traits are determined by genes located on the sex chromosomes (X and Y). Since females have two X chromosomes (XX) and males have one X and one Y chromosome (XY), the inheritance patterns for sex-linked traits differ between males and females:
- X-linked Recessive Traits:
These traits are carried on the X chromosome.
Males are more commonly affected because they have only one X chromosome. If a male inherits a recessive allele on the X chromosome from his mother, he will express the trait.
- X-linked Dominant Traits:
These traits are less common than X-linked recessive traits.
Both males and females can inherit and express the trait if they have at least one dominant allele.
- Y-linked Traits:
These traits are very rare and are inherited only through the Y chromosome.
They are passed down from father to son.
Example: Y-linked traits include male-specific traits like male infertility due to mutations on the Y chromosome.
Know how to perform autosomal and X-Linked monohybrid crosses.
A cross of two individuals that differ by one trait
Punnett Square: A 2 x 2 chart used to determine the probability of results when two individuals are crossed
P Generation: The parents in the initial cross
F1 Generation: The offspring of the first generation cross
F2 Generation: The offspring of the second generation cross
(1)The possible gametes produced by the parents are written at the top and along the side
(2) The gametes are combined to produce all of the possible F1 genotypes
(3) Genotype and Phenotype Ratios are expressed
- When a cross involves parents that are homozygous for a trait, the F1 generation will always be heterozygous
- The F2 generation will always have a genotypic ratio of 1:2:1 (1 homozygous dominant: 2 heterozygous: 1 homozygous recessive)
- The F2 generation will always have a phenotypic ratio of 3:1 (3 dominant: 1 recessive)
Be able to complete a dihybrid cross for both the F1 and F2 generations.
Dihybrid cross
- Used to determine the inheritance pattern of two different traits
- Remember the Law of Independent Assortment: traits are on different chromosomes, therefore they are inherited separately
- This gives us 16 possible genotypes, and 4 possible phenotypes with each dihybrid cross!
What is artificial selection? What are some ways this process is used today?
Selective pressure exerted by humans on populations as way to improve or modify desirable traits
Examples:
● Cats or dogs bred for appearance
● Cows bred for more muscle for meat
● Chickens bred to produce more eggs
Artificial selection is used by farmers to:
1) Increase nutritional value
2) Increase production and the economy for countries dependent on crops
3) To be drought-resistant or pest-resistant
Consequences of AS
- Monoculture: only one crop is grown in the same space at the same time producing genetically identical plants. This will reduce genetic diversity
If a new disease infests the crops most of them will be affected
Positive Consequences
- Growing requirements
- Maintenance
- Pest control
- Standardized harvesting
- Greater yield
Negative Consequences
- Weak soil
- More fertilizer
- Spread of pests
- Spread of diseases
- More pesticides
Gene Banks contain seeds from early plant ancestors. These seeds can survive for long periods of time and can be introduced into modern plants if needed Goal: preserve genetic diversity
What is the difference between convergent and divergent evolution?
convergent evolution
similar traits arise because different species independently adapted to similar environmental conditions (example: birds and bats both have wings, but they don’t have a common ancestor)
Divergent evolution
species similar to the ancestral species diverge and become distinct due to changing environmental conditions (example: birds have a common ancestor but they have different types of beaks based on their diet)
What is the difference between homologous, analogous, and vestigial structures?
Homologous Structures
- Structures that have similar structural elements and origin
- May have a different function
- Originate from a common ancestor
○ Example: hair on mammals
Analogous Structures
- Structures that do not have a common evolutionary origin
- Perform similar functions
- Provide evidence for adaptations to suit the environment
○ Fins on a dolphin vs. fins on a fish
Vestigial structure
-reduces versions of what was once functional structures in an ancestral species
Know examples of incomplete and codominance
Incomplete dominance- MIX OF TWO COLORS
- Neither allele completely masks the other
- Both alleles are equally dominant, causing a completely new phenotype that looks like a blend of the other two
- Example: flower colour in snapdragon plant
- Snapdragon Flower Color:
In snapdragons, flower color shows incomplete dominance.
Red (RR) and white (WW) homozygous flowers produce pink (RW) heterozygous offspring.
- Andalusian Chickens:
Feather color in Andalusian chickens exhibits incomplete dominance.
Black (BB) and white (WW) homozygous chickens produce blue (BW) heterozygous offspring.
Codominance- TWO COLORS BESIDE EACH OTHER
- Both dominant alleles are equally expressed at the same time in a heterozygote
- Example: Hair colour in a roan cattle
ROAN: an animal that has a fur coat of
alternating hair colours expressed at the
same time!
- ABO Blood Group System:
The ABO blood group system in humans demonstrates codominance.
Individuals with genotype IAIB have both A and B antigens on their red blood cells, expressing both alleles equally.
- Roan Cattle Coat Color:
Coat color in roan cattle is an example of codominance.
Red (RR) and white (WW) homozygous cattle produce roan (RW) heterozygous offspring, which have both red and white hairs evenly distributed throughout their coat.
What is natural selection? What are the three types?
Natural selection only occurs when there is genetic diversity within a species
- If an organism produces offspring that also survive to reproduce, that organism is said to be fit for the environment
- Fitness: the contribution that an individual makes to the next generation by producing offspring that will survive long enough to reproduce
- High Fitness: many viable offspring
- Low Fitness: few viable offspring
- Natural selection is situational because it depends on the environment and available traits
- It does not anticipate the change in the environment and has no direction or purpose
- There are times when one trait may have no relevance for survival until a selective pressure turns that trait into a selective advantage
3 types:
-Stabilizing selection: favors intermediate phenotypes and acts against extreme variations of the phenotype
-Directional selection: favors phenotypes at one extreme over the other (especially in environmental change)
-Disruptive selection: favours the extremes of a range of phenotypes which can cause the intermediate to be eliminated
What are the possible genotypes and phenotypes associated with blood type? What kind of inheritance patterns are evident when looking at blood types?
- One single gene determines a person’s blood type by coding for a type of antigen protein (molecule that stimulates the body’s immune system) to attach to the red blood cell membrane
- The gene is designated, I and has three
common alleles: IA , IB, i - Presence of allele A produces an A antigen
- Presence of allele B produces a B antigen
- Presence of both alleles A and B produce both antigens
- Presence of allele i produces no antigen
Genotype IAIA or IAi: Blood type A (phenotype).
Genotype IBIB or IBi: Blood type B (phenotype).
Genotype IAIB: Blood type AB (phenotype).
Genotype ii: Blood type O (phenotype).
Be able to contrast the findings of Charles Darwin and Jean-Baptiste Lamarck.
Jean-baptiste Lamarck
- Suggested species increased complexity and became better adapted to their environment over time until they achieved perfection
- Proposed the idea of the inheritance of
acquired characteristics where characteristics acquired in an organism’s lifetime could be passed onto offspring
- He would explain a giraffe’s long neck by: Giraffes had to stretch their neck to
reach the top of trees (food)
- This learned characteristic was useful
and was passed onto future generations
- Use vs. Misuse (things that are used
will be passed on, things that are not
used will not be passed on)
Charles Darwin
- Travelled the coast of South America and made natural and geographical observations
- Proposed the Theory of Natural Selection→ life has changed and continues to change based on natural pressures
His observations:
1. Flora and fauna of the different regions were distinct from those in Europe
→ Rodents in South America (SA) were similar to each other but different from other continents
2. Fossils of extinct animals looked very similar to living animals
→ Extinct glyptodon and modern armadillo from SA
3. Finches and other animals Darwin saw on the Galapagos Islands closely resembled animals he had observed on the West Coast of South America
4. Galapagos species (tortoises and finches) looked identical at first but:
→Varied slightly between islands
→ Each appeared to be adapted to eating different types of foods (different beak size and shape)
5. Through his experience with artificial selection (breeding pigeons, studying dogs and flowers), he knew it was possible for traits to be passed down from parent to offspring.
- From here, using the idea of survival of the fittest he developed the theory of Natural Selection.
As written in his book The Origin of Species:
1) Organisms produce more offspring than are able to survive
2) Individuals of a population very extensively
3) Individuals better suited to local conditions survive and reproduce
4) Processes for change are slow and gradual
- Darwin never used the word evolution, he called it descent with modification
- To Darwin evolution meant progress
- Natural Selection does not demonstrate progress; it has no set direction
Know the sources of evidence for evolution and examples of each.
the fossil record
-Specific fossils are found within specific layers
-(strata) of sedimentary rock
-Paleontologists use this to determine dates
- Not all organisms appear in the fossil record at the same time
- Transitional fossils are always being researched and found to fill in the space between the past and the present, where some organisms developed differently.
biogeography
- The study of the geographical distribution of species
- Geographically close environments are more likely to have related species
- Animals found on islands closely resemble animals on the nearest continent
- Fossils of the same species can be found on the coastline of neighboring continents
anatomy
Homologous Structures
- Structures that have similar structural elements and origin
- May have a different function
- Originate from a common ancestor
○ Example: hair on mammals
Analogous Structures
- Structures that do not have a common evolutionary origin
- Perform similar functions
- Provide evidence for adaptations to suit the environment
○ Fins on a dolphin vs. fins on a fish
Embryology
-The study of prebirth stages of an organism’s development
-This helps us to see evolutionary ancestors between organisms
DNA
- comparing genetic sequences can help determine similarity
- Two organisms with similar DNA suggests that they inherited these traits from a common ancestor
