Genetics Flashcards
Heredity
Passing of traits from parents to offspring
Genetics
is the study of heredity and variation
In a chromosome, genetic information is stored in a molecule of________
DNA
DNA
Has set of chemical instructions for the cell; a gene
Gene
Portion of DNA that contains information that helps produce trait
locus (plural - loci)
Each gene occupies a specific location on a chromosome
Nucleic acids
Are long polymers that hold information to specify the structure of proteins to be made in a cell
These determine the characteristics and functions a cell will have
Structure of nucleic acids
Made of subunits called nucleotides
Nucleotides are made up of 3 smaller building blocks
- Five Carbon sugar ( in a ring )
- Phosphate group
- Nitrogen Base
What are the 2 types of Nucleic Acid?
- DNA
Found in the nucleus and is the main component of genes
The sugar in the nucleotides are called deoxyribose sugar (missing oxygen from 2nd carbon)
Adenine —> Thymine
Guanine —> Cytosine
- RNA
Also found in the nucleus, and contains instructions for making proteins.
The sugar in the nucleotides is called ribose sugar.
Guanine —> Cytosine
Adenine —> Uracil`
2 types of Nitrogen Bases
Purines: Adenine and Guanine (large, double-ringed compounds)
Pyrimidines: Cytosine and Thymine (smaller, single-ringed compounds)
Chromatin
thread-like structure made up of DNA and proteins in the nucleus of a eukaryotic cell
Chromosome
structure in the nucleus of a eukaryotic cell that carries genes, formed when chromatin condenses
Chromatid
each of the two identical chromosome strands in a replicated chromosome attached by their shared centromere
Cells reproduce through controlled growth and division for 3 main functions:
Growth
Maintenance to replace dead/dying cells
Repair of tissues/organs
what are the 3 stages of cell cycle
Interphase
Mitosis
Cytokinesis
Interphase
Period between cell divisions
Cell undergoes growth, duplicates hereditary information and prepares for mitosis
Most of cell life is in this stage, misnamed as “resting phase”
What phases is Interphase broken down into? and describe each phase.
G1 phase (first gap): cell is growing and preparing for replication
S phase (synthesis): genetic information is replicated
G2 phase (second gap): final preparation for cell division
Once cell begins to divide:
The nucleus must undergo mitosis
Cytokinesis occurs at the end of the cycle
Mitosis
stage of the cell cycle during which genetic information is divided equally into 2 nuclei
Occurs in somatic cells
Any cell that is not a reproductive cell
Occurs in most tissues that must replace themselves (eg. skin)
Occurs when a parent cell divides to produce two daughter cells
Daughter cells are genetically identical to parent
What are the phases of mitosis?
Prophase, Metphase, Anaphase, Telophase
Prophase
Chromatin condenses into chromosomes, join at the centromere
Nuclear envelope breaks down
Centrioles move to poles, producing microtubules (spindle fibres)
Metaphase
Spindle fibres begin moving and aligning chromosomes
Chromosomes line up along the equator (metaphase plate)
Chromosomes are condensed and thick
Anaphase
sister chromatids separate from one another producing 2 single stranded chromosomes
Spindle fibres shorten as they pull the chromosomes to opposite poles
Telophase
Chromosomes decondense
Spindle breaks down
Nuclear envelope forms
Cleavage furrow begins in animal cells or cell plate forms in plant cells
Mitosis ends with telophase
Cytokinesis
Division of cytoplasm
Cleavage furrow pinches off
Formation of two identical daughter cells
Somatic Cells
body cells, that have a diploid number of chromosomes (two sets)
Cancer
Abnormal cell division; out of control, continuous
What are the 2 types of Tumors? And describe each of them
Benign tumours show no signs of spreading
Malignant tumors are capable of spreading and invading new tissues (metastasis)
How can you treat cancer?
Therapy: radiation, chemotherapy, immunotherapy
Sister Chromatids
are when two chromatids are held together by a centromere (they are called sister chromatids because they contain the same type of genes on them) -> “double-stranded” chromosome
Homologous Chromosomes
matching pairs of chromosomes, similar in size and shape and have the same genes, arranged in the same order
Consist of a chromosome from the male parent and a chromosome from the female parent.
Meiosis
Only occurs in eukaryotes that reproduce sexually
Only occurs in organisms that are at least diploid
Undergoes TWO divisions
1 parent cell produces 4 gamete cells
Each gamete cell contains different genetic information
What does the creation of gametes rely on?
The creation of gametes relies on meiosis, a specialized process of cell division that produces gametes!
How many stages are there in meiosis
The process of meiosis, involves two stages of cell division which in turn reduces the number of chromosomes to half the amount present (becomes haploid).
Premeiotic Interphase
DNA replicates
Two identical copies of each chromosome are made, attached at centromere
Each copy is called a sister chromatid
Prophase I
Homologous chromosomes pair together, called a tetrad (each chromosome made of 4 chromatids held together by kinetochore)
Each sister chromatid intertwines with a sister chromatid from matching homologous chromosomes, called synapsis
Once synapsis occurs, intertwined chromatids from different chromosomes break and reattach to each other
CROSSING OVER: Results in recombination of genetic information between non sister chromatids, at random points called chiasmata
Centrioles move to opposite poles, and spindle fibres appear
Metaphase I
Spindle fibers attach to kinetochore of tetrad
Tetrads line up along equatorial plate (middle)
Independent assortment occurs
Randomly lines up in the middle
Anaphase I
Tetrad is pulled apart as each chromosome moves towards the opposite pole
Chromosomes are pulled apart at the kinetochore
Sister chromatids are still intact
Telophase I
Chromosomes reach poles
Nuclear membrane reforms
Spindle fibres disintegrate
Cytokinesis for meiosis
Cytoplasm and organelles divide in half
Each daughter cell is haploid (n)
One chromosome from each original homologous pair, HOWEVER, sister chromatids still exist
Second Meiotic Division: Meiosis II
There is no replication of DNA (interphase II)
Chromosomes in daughter cells of meiosis I are in the form of sister chromatids
No crossing over occurs (no homologues to synapse)
Prophase II
Chromosomes condense
Centrioles move to opposite poles
Spindle fibres appear
Metaphase II
Sets of chromatids move to equator
Centromeres divide
Anaphase II
Chromatids move to opposite poles
Telophase II
Chromosomes unwind, and nuclear envelope forms.
Produces 4 haploid cells (sperm or ova) after cytokinesis
Cytokinesis II
Product: 4 cells, each with a haploid amount of chromosomes
They are all genetically different!
2 Methods of Genetic Variability in Meiosis
During Metaphase I of meiosis, homologous chromosome pairs separate randomly.
Some gametes may receive all paternal chromosomes or all maternal or a mixture of both.
Meiosis is an important source of GENETIC VARIABILITY!
Another way in which meiosis contributes to variability is from crossing over during prophase I
Gamete Formation (Gametogenesis)
At the end of meiosis, gametes are formed which differentiate into specialized cells
Sperm formation (spermatogenesis):
Diploid spermatogonia → primary spermatocytes → 4 spermatids
Egg formation(oogenesis):
Diploid Oogonia → primary oocytes → 1 egg + 3 polar bodies
Aneuploidy
Error in meiosis
Occurs when chromosomes do not separate properly during meiosis leading to cells having too many or too few chromosomes
Nondisjunction
Failure of homologous chromosomes to separate in meiosis I
Failure of sister chromatids to separate in meiosis II
Monosomy
fertilized cell is missing a chromosome
Trisomy
fertilized cell has an extra copy of a chromosome
Polyploidy
Every chromosome is duplicated
Can be 3n, 4n , etc
Nondisjunction Disorders
Results in cells not being able to function properly
Responsible for a lot of human genetic disorders
Eg. Down’s syndrome (trisomy 21): result of nondisjunction of chromosome 21.
The offspring receives 3 copies instead of 2.
An excess of genetic information causing people with this disorder to have mental and physical differences/challenges
List some of the Nondisjunction Disorders
Responsible for:
Down Syndrome (trisomy 21)
Physical/mental challenges
Turner Syndrome (One X chromosome)
Females born sterile
Klinefelter Syndrome (2 X and 1 Y chromsomes)
Males usually sterile; display feminine traits
Patau Syndrome (trisomy 13)
Developmental problems (brain, kidney, heart)
Karyotyping
Karyotyping can be used to diagnose chromosomal abnormalities prenatally
Cells for testing can be collected from the amniotic fluid (amniocentesis) or from villi along the lining of the uterus (chorionic villus)
Scientists count, compare, arrange chromosomes to see if there are any issues
Normally recommended for women over the age of 35
Why is a karyotyping important for women over the age of 35?
May be due to oocytes stopping at prophase I until ovulation as part of oogenesis
This results in a higher change for nondisjunction in meiosis I from older organelles which age with the individual
Inheritance
is the process of genetic transmission of a trait/characteristic from parent to offspring.
Allele
A specific form of a gene (eg. purple flower, white flower)
homozygous
If an individual has two of the same alleles (eg. both dominant or both recessive)
heterozygous
If an individual has two different alleles (eg. one dominant, one recessive) it is considered
Genotype
genetic makeup of alleles
Phenotype
appearance of a trait
What is the purpose of monohybrid crosses?
Mendel recorded his observations of peas using thousands of monohybrid crosses.
These crosses are between two organisms (in this case pea plants) with only ONE characteristic that is different.
Monohybrid crosses illustrate all of the possible combinations of gametes from a given set of parents.
They are used to calculate the probability of inheriting a particular trait.
Law of Segregation
Organism inherits 2 copies of genes, one from each parent
Organism only donates one copy of each gene
Law of Independent Assortment
Law of Independent Assortment states that if genes are on separate chromosomes, they are inherited independently of each other (unlinked)
dihybrid cross
A dihybrid cross determines genotypic and phenotypic combinations of offspring for two particular genes that are unlinked.
Two genes, each have two alleles, there can be up to four gamete combinations per parent
