Genetics Flashcards
What is DNA?
A molecule that carries genetic information (deoxyribonucleic acid)
What is the purpose of a chromosome?
It contains a molecule of DNA where genetic information is stored DNA is more precisely in long fibers called chromatin which is the material that makes up a chromosome
What is a gene?
It is a segment of a DNA molecule that codes for a particular trait; found at a specific location on a chromosome. -Genes also code for proteins -Mistakes in genes=mistakes in proteins
What is the structure of DNA?
DNA consists of a long chain of subunits called Nucleotides. DNA is a molecule composed of two Polynucleotide chains that coil around each other to form a double helix that carries genetic instructions.(It is a double helix)
What is the composition if a nucleotide?
DNA consisting of a long chain of subunits (smaller units)
What are the 3 parts of a nucleotide?
- A ring-shaped sugar called deoxyribose
- A phosphate group
- A nitrogenous base (made of carbon and nitrogen)
What is the sugar-phosphate backbone (handrails)?
Nucleotides link together by phosphodiester bonds to create a polynucleotide chain.
What are nitrogenous bases (the stairs)?
The nitrogenous base form base-pairs via hydrogen bonding and join the two complimentary strands in DNA.
What are nitrogenous bases joined to?
The DNA backbone by a glycosyl bond..
What are the 2 types of nitrogenous bases?
Pyrimidine bases (single ring) and Purine bases (double ring)
What are all the pyrimidine bases?
Uracil (U) (found in RNA) Thymine (T) Cytosine (C)
What are all the purine bases?
Adenine (A) Guanine (G)
What nitrogenous bases bond with each other?
Adenine (A) always bonds with Thymine (T), Cytosine (C) always bonds with Guanine (G) *Note: The two strands are antiparallel (they start in opposite directions)
How many chromosomes do humans have?
Human body cells have 46 chromosomes (2 pairs of 23). 44 of the chromosomes are autosomes. 2 are sex chromosomes
What are the stages of the cell cycle?
- Growth Phase 1
- Synthesis Phase
- Growth Phase 2
- Mitotic Phase (Mitosis occurs here)
What are the stages of mitosis?
PMAT (Prophase, Metaphase, Anaphase, and Telophase)
What happens during prophase in Mitosis?
- -Chromosomes begin to shorten and thicken
- -Nuclear membrane dissolves
- -Centrioles move to opposite poles of the cell
- -Spindle fibers attach to the centromeres, which hold the sister chromatid together.
What happens during metaphase in mitosis?
-Chromosomes line up in the middle of the cell
What happens during anaphase in mitosis?
-Sister chromatids are pulled apart by spindle fibers and move to opposite ends of the cell
What happens during telophase in mitosis?
- -Nuclear membranes form around the chromosomes on either end of the cell
- -The cell pinches in the middle (Then Cytokinesis takes place where it divides the cytoplasm of a parental cell into two daughter cells)
What are telomeres?
Every time DNA replicates, a small amount of DNA is lost. To help reduce this loss, the chromosomes have protective caps called telomeres. After many many many many divisions, the telomeres become too short and the cell can no longer divide.
What are genetically modified organisms (GMO’s)?
Genetically modified organisms (GMOs) involves inserting a desired gene from one species into the DNA of another species. (Ex. healthy fats genes inserted into pigs to make them more healthy)
In which type of cells does mitosis occur?
Eukaryotic cells
What is the result of mitosis?
A parent cell has divided successfully into two identical daughter cells.
What are sister chromatids?
The identical copy of a single chromosome that remains attached to the original chromosome at the centromere.
What is cloning?
The process of producing one individual that is genetically identical to another, using a single cell or tissue. (Can be a natural process or unnatural)
What is a karyotype?
a picture of all the chromosomes in a cell.
What are all the stages of meiosis?
Prophase I, Metaphase I, Anaphase I, Telophase I, Prophase II, Metaphase II, Anaphase II, Telophase II.
What happens during prophase l in meiosis?
- -Homologous chromosomes line up beside each other, creating sister chromatids
- -Spindle fibres form, centrioles form
- -Crossing over occurs
What happens during metaphase l in meiosis?
- -Homologous chromosomes line up at the middle of the cell
- -*In meiosis, homologous chromosomes line up beside each other
What happens during anaphase l in meiosis?
Homologous CHROMOSOMES are separated and move towards opposite poles (i.e. the chromosome 1s are separated, the chromosome 2s are separated, etc.) Independent assortment occurs: some of your chromosomes from your mother go to one cell, and some go to the other
What happens during telophase I in meiosis?
- -Two nuclei are formed: each new cell now has 2 copies of each chromosome.
- -Spindle fibres break down
- -At this point, the sister chromatid are identical
What happens during prophase II in meiosis?
- -Spindle fibres form
- -Centrioles form
*Note sometimes before prophase II, Interphase II occurs.
What happens during metaphase II in meiosis?
-Chromosomes line up up at the middle of the cell
What happens during anaphase II in meiosis?
- -Chromosomes separate
- -Notice that this time the sister CHROMATIDS split apart, meaning we will only have half the number of chromosomes in each daughter cell
What happens during telophase II in meiosis?
- -Nuclear membrane forms
- -4 daughter haploid cells are produced (sperm or egg cells)
- -Each cell has one of each homologous chromosome
- -Each cell is unique because of: Independent assortment, crossing over
What are the types of cells that undergo meiosis?
Sperm and egg cells will undergo meiosis in order to reproduce.
What is the result of meisosis?
Haploid gametes are formed.
What are diploids?
Diploids have two sets of each chromosome. For each pair, one chromosome is from your mother and one chromosome is from your father
What are haploids?
Haploid cells have one of each chromosome. Each chromosome could be from either your mother or father.
What is fertilization?
The haploid sperm and haploid egg join together to form a diploid zygote.
What are Homologous Chromosomes?
A pair of chromosomes that code for the same feature
What is crossing over?
A process to ensure a genetically unique gamete (sperm or egg), the homologous chromosomes exchange random sections of DNA
How is genetic variation achieved in meiosis?
-Crossing over -Independent assortment
What is spermatogenesis?
When sperm is created (4 non-identical haploid sperm cells)
What is oogenesis?
When an egg is created (4 non-identical haploid cells, one ovum and three are polar bodies)
What is a sex chromosome?
A chromosome that participates to determine the sex of the child. (XX = Female, XY = Male)
In which meiosis phases do nondisjunction mutations occur?
Nondisjunction mutations in Anaphase I and Anaphase II
What happens in anaphase I that causes nondisjunction mutations?
- -In anaphase I, sometimes the spindle fiber snaps, and both homologous chromosomes go to one side.
- -This eventually creates 2 daughter cells with too many chromosomes (24), and 2 with not enough (22).
What happens in anaphase II that causes nondisjunction mutations?
- -In anaphase, sometimes the spindle fiber snaps, and both sister chromatid go to one side
- -This leaves one daughter cell with too many chromosomes (24) and one with not enough (22)
What is down syndrome?
Down syndrome is the most common disorder caused by nondisjunction. People with down syndrome have a third copy of chromosome 21. This is why it is known as trisomy 21.
What is the risk factor of down syndrome?
The risk factor increases with age.
What are some of the causes of down syndrome?
Due to the spindle fibers in the egg becoming more brittle and weak.
What are the symptoms of down syndrome?
-Heart defects (in approx 50% of cases) -Small jaw -Intellectual delay (including language and speech) -Flattened face -Atlanto-axial instability (joint between C1 and C2 vertebrae) -Behavioral symptoms include stubbornness and impulsivity
Describe the karyotype of someone with Patau syndrome.
Individuals with Patau Syndrome have a third copy of chromosome 13. Known as trisomy 13
Describe the karyotype of someone with Edwards syndrome.
Individuals with Edwards Syndrome have a third copy of chromosome 18. Known as trisomy 18
Describe the karyotype of someone with Klinefelter syndrome.
-Affects only males -Males with Klinefelter Syndrome have an extra chromosome X (XXY)
Describe the karyotype of someone with Turner syndrome.
-Affects only females -Girls with Turner Syndrome have only one X chromosome
What is a positive mutation?
Mutations that have a positive effect in the organism that it occurs in (ex. Lactose tolerance)
What is a neutral mutation?
Change in the DNA sequence that has no positive or negative effect on the organism.
What is a negative mutation?
Altered gene that has a negative effect on the survival of an organism (ex. cancer)
What is a point mutation?
Point mutations change a single nucleotide
What is translocation?
A fragment of one chromosome attaches to another chromosome.
What is deletion?
A fragment of a chromosome is lost during DNA replication. Results can be severe if code is lost for important proteins.
What is duplication?
One or more genes in a chromosome are repeated.
What is inversion?
A series of genes are reversed.
What are spontaneous mutations?
Spontaneous mutations occur randomly
What are induced mutations?
Induced mutations are caused by exposure to an outside factor (ex. radiation, smoking)
What is heredity?
The passing traits from parents to offspring
Who is Gregor Mendel?
Studied heredity by crossing pea plants with different physical traits.
What are the two reasons for using pea plants in Mendel’s tests?
- Garden peas vary on seven characteristics that are expressed as one of two traits only
- Pea flowers have both male and female reproductive organs. Garden peas are both self-fertilizing (self-pollinate) and cross-fertilizing (pollinate others)
What is Mendel’s law of heredity?
- For each gene (e.g. gene for the characteristic of flower colour), an organism carries two alleles: one from each parent.
- Each pair of alleles segregates (separates) during the formation of sex cells.
- Each parent contributes one allele for each gene during cross-fertilization (sperm and egg).
- The dominant allele is always expressed even when the a recessive allele is present.
What is an allele?
A specific form of a gene.
What is homozygous?
The individual has two alleles for a particular gene that are the same.
What is hetrozygous?
The individual has two different alleles for a gene.
What is a dominant allele?
-The allele that, if present, is ALWAYS expressed. -Example: For plant height: TT or Tt
What is a recessive allele?
The allele that is expressed ONLY IF it is NOT in the presence of the dominant allele i.e. if the individual is homozygous for the recessive allele.
What is genotype?
the genetic makeup of an individual. -The Code -The set of alleles that an individual has
What is phenotype?
An individuals’ outward appearance with respect to a specific characteristic. -What it looks like! -The alleles that are expressed determine an individual’s phenotype
What is P?
Parent generation (parents plants used)
What is F1?
First offspring generation (children of P generation)
What is F2?
Second offspring generation (grand-children, offspring of F1 generation)
What is a Punnett square?
A diagram that summarizes every possible combination of each allele from each parent.
What is a monohybrid?
The offspring of two different true breeding plants that differ in only one characteristic.
What is a monohybrid cross?
-A cross designed to study the inheritance of only one trait -To track the inheritance of a single trait, Mendel crossed true breeding plants that differed from each other in only one characteristic, such as flower colour.
Describe Mendel’s monohybrid cross.
-Mendel took two pure-bred plants that only differed in one trait (flower colour). -Parent A was a pure-bred plant with purple flowers. -Parent B was a pure bred plant with white flowers
What were the results of Mendel’s experiments?
-Mendel allowed the F1 generation to self pollinate. -F2 generation consisted of plants with purple flowers and white flowers. -This meant that the trait for white flower had not disappeared but had somehow been masked. -Experiment was repeated many times and the results were consistently that the traits in the F2 generation were in a ration of 3:1 (75% purple & 25% white).
What is a test cross and how does it work?
-A cross used to determine the genotype of an individual expressing a dominant trait/phenotype. -Breed the unknown phenotype with a homozygous recessive (pp) to determine the identity of the unknown allele.
What is the Law of Segregation?
A scientific law stating that:
- Organisms inherit two version of genes, one from each parent.
- Organisms donate only one version of each gene to their gametes because the genes separate during gamete formation (meiosis).
What is incomplete dominance?
A situation where neither allele dominates the other and both have an influence on the individual; results in partial expression of both traits. (Ex. a red flower and white flower could create a pink flower)
What is codominance?
A situation where both alleles are expressed fully to produce offspring with a third phenotype.
What are genes with multiple alleles?
Traits that have more than 2 possible alleles (ex. blood types)
What are all the blood types?
- Carbohydrate A (Blood type A)
- Carbohydrate B (Blood type B)
- Both carbohydrates (Blood type AB)
- No carbohydrates (Blood type O)
- *I^A and I^B are dominant to i and I^A and I^B are codominant
What are blood antibodies?
Proteins in blood made by the immune system to fight against a pathogen. Antibodies determine which type of blood can be received in a blood transfusion.
What blood type is the universal donor?
Type O is the universal donor because it has no surface carbs, meaning there is nothing to attack
What blood type is the universal acceptor?
Type AB is the universal acceptor because it has no antibodies so it won’t attack anything
What are polygenetic traits?
Traits influenced by multiple genes. Polygenic traits will display a wide range of phenotypes due to the additive effect of many genes.
What role does the environment play on phenotype?
The environment can play a role in the phenotype. Ex. If hydrangeas are grown in acidic soil, they have blue flowers. If they are grown in basic soil, they have pink flowers
What are sex linked traits?
Any gene located on a sex chromosome is called a sex linked gene (X and Y chromosomes)
Describe the differences between X and Y chromosomes.
Nearly all of these genes are located on the X chromosome, while very little genetic information is located on the Y chromosome.
What are some examples of sex-linked disorders (attached to the X chromosome)?
-Colour blindness -Hemophilia -Duchenne -Muscular -Dystrophy -Fragile X -Rett Syndrome
What are X-linked dominant disorders?
If a disorder is dominant, then the disordered X chromosome is dominant over the normal X chromosome. X^D is dominant over X
XX^D displays the disorder
X^DX^D displays the disorder
X^DY displays the disorder
What are X-linked Recessive Disorders?
If the disorder is recessive, then the regular X chromosome dominates over the disordered X chromosome, but the Y chromosome does not. XX^d does not display the disorder X^dX^d displays the disorder X^dY displays the disorder
What is a carrier?
An individual who carries and is capable of passing on a genetic disorder that may or may not show symptoms. Women are usually carriers as they usually will not display symptoms of a disorder but are able to pass it to a child.
Can you remember sex-linked Punnett squares?
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