LT’s #1,2,3: quiz #1 Flashcards
Genetics
Study of heredity and variation of inherited characteristics
DNA
DNA stores the hereditary information in organisms. It is the information carrying molecule located in the nucleus of eukaryotic cells.
- long chain of nucleotide building blocks
- pair of nucleotide chains twist together to form double helix (A&T, G&C)
Chromatin
Term used to describe the genetic material during interphase. All of the DNA molecules and the associated proteins in the nucleus
Gene
Segment of DNA that encodes for a specific piece of information/trait (ie. gene for eye colour) Occupies specific location (locus or loci) on a chromosome
Diploid
Cells have 2 copies of each chromosome (2n)
ie. human somatic cells=46 chromosomes
Haploid
Cells have half the number of chromosomes (n)
ie. human gametes=23 chromosomes
Chromosomes
The individual coiled up molecules of DNA that contain thousands of genes. Found in nucleus of eukaryotic cells.
Homologous Chromosomes
Chromosomes that code for the same info (not genetically identical) Pair of chromosomes carrying different alleles of the same genes. (Matching pairs of chromosomes, similar in size and carrying the info for the same genes)
Chromatid
A single “arm” in a duplicated chromosome
Sister Chromatids
The two chromatids of a duplicated chromosome that are attached together at their centromere. Genetically identical
Cell Cycle
A continuous sequence of cell growth and division for all body (somatic) cells. Consists of three stages: 1) Interphase 2)Mitosis 3)Cytokinesis
For most of cell cycle DNA exists as chromatin
Interphase
The period between cell divisions. Cells undergo their normal activities of obtaining energy, synthesizing products and repairing damage.
The Three Stages of Interphase
1) G1 phase- “gap 1 phase” Cells carry out normal processes and prepare for S phase.
2) S phase- “synthesis phase” DNA is replicated for cell division. (chromatin replicate to form sister chromatids)
3) G2 phase- “gap 2 phase” Cells begin final preparations for cell division.
Mitosis
The process of cell division. Genetic material in nucleus divided equally into 2 new nuclei. There are 4 main stages (PMAT)
- occurs in somatic cells
- purpose of process is to grow, repair injured organisms, replace old+dead cells
- 1 cell division
- 2 cells produced that are genetically identical to parent cell
- 46 chromosomes in daughter cell (diploid number)
Prophase
- nuclear membrane dissolves
- preparing for division
- chromatins condense
Asexual Reproduction
Production of offspring from single parent; genetic makeup of offspring is identical to parent
ie. copperhead snake and starfish (can produce sexually or asexually)
Advantages of Asexual Reproduction
- no finding mate
- no specialized mating behaviours
- no specialized anatomy
- heredity direct and invariable
Sexual Reproduction
Production of offspring from fusion of 2 sex cells (usually from 2 different parents); genetic makeup of offspring is different from either parent (merging of 2 haploid gametes)
Advantages of Sexual Reproduction
Variable offspring and traits to adapt to change
Metaphase
-chromosomes line up in middle of cell
Anaphase
The chromatids are separated by the spindle fibres which are attached for eh centrioles and the new chromosomes are pulled to opposite sides of the cell.
Telophase
Nuclear membrane reforms. There are 2 nuclei. Chromatins begin to uncoil.
Cytokinesis
The division of the cytoplasm and organelles. Occurs after mitosis.
Cell Division
The mother cell divides into 2 identical daughter cells.
Why Mitosis?
Cell division occurs in all of our body cells expect for our sex cells. Our body cells contain 46 chromosomes (23 pairs)
Why do our body cells need to divide?
- allows a zygote (fertilized egg) to mature into an embryo
- helps an organism physically grow bigger (ie. humans grow taller)
- helps to repair an injured organism
- replaces old and dead cells
Meiosis
Division process that prevents “doubling” of genetic material from occurring. Creates gametes with half the number of chromosomes (haploid cells) It is the division of the nucleus (and the chromosomes inside of it) in sex cells. One cell divides into 4 cells with a lower chromosome number. This process happens continuously in all living things that are made up of more than 1 cell, after puberty. In males this process leads to the formation of sperm cells and in females leads to one egg cell at a time.
- occurs in sex cells (germ cells)
- purpose is to produce genetic variation and create gamete cells
- 2 cells divisons
- 4 cells produced that are genetically different from partent cell
- haploid chromosome number in daughter cells (23 chromosomes)
Germ Cells
Location of meiosis in body. Males (testicles) Females (ovaries)
Meiosis: Interphase
Chromosome duplicates and is waiting to divide
What links together the two sister chromatids after DNA replication?
Centromere
Prophase I
- chromosomes condense
- nuclear membrane dissolves
- spindle fibres form
- centrioles move toward poles
- homologous pairs line up in tetrads
- crossing over occurs (chromosome segments are exchanged)
Metaphase I
Pairs of homologous chromosomes line up in the centre of the cell and spindle fibres attach to each pair of sister chromatids
Anaphase I
Homologous pairs are pulled apart and the homologous chromosomes are moved to opposite sides of the cell
Telophase I & Cytokinesis
- chromosomes gather at opposite sides of the cell
- cytoplasm divides
- 2 new genetically different daughter cells are formed each with 2 chromosomes (haploid)
Prophase II
- a new spindle forms around the chromosomes
- the cell prepares to divide
- nuclear membrane breaks down
- centrioles begin to move to poles
Metaphase II
Sister chromatids line up at centre of cell
Anaphase II
- centromeres divide
- chromatids are pulled apart to opposite sides of the cell
Telophase II & Cytokinesis
- a nuclear membrane forms around each set of chromosomes
- cytoplasm divides
- chromosomes uncoil
- 4 new daughter cells are produced with 2 chromosomes in each (haploid, n=2)
- 1 copy of each chromosome
- 1 allele of each gene (different combinations of alleles for different genes along the chromosome)
Crossing Over
In the tetrad, chromatids often break off at the end and swap places with the sister chromatid. This process allows for genetic variation. The location of recombination is called the chiasma.(exchange of genetic info between on sister chromatids of a homologous pair during prophase I)
Independent Assortment
The random distribution of a chromosome to a daughter cell depending on how the chromosomes line up in Metaphase 1&2.
-2^n
n=# of chromosome pairs
-2^2=4 gamete options
-2^23=8388608 gamète options
Tetrad
A pair of homologous chromosomes, each with 2 sister chromatids
Importance of Meiosis
- creates genetically different gametes
- each daughter cell created is different
- variation and diversity of living organisms
Gametogenesis
The development of haploid cells into gametes. This process differs between males and females
Spermatogenesis
- occurs in male testes
- results in four genetically different sperm cells
- during this process sperm grow a tail and gain the ability to swim
Oogenesis
- occurs in female ovaries
- results in the production of one viable and three non viable eggs (polar bodies)
- polar bodies result from unequal division of cytoplasm (there is only enough cytoplasm to support one egg)
What’s a mistake in meiosis?
- too many or not enough chromosomes which can lead to genetic disorders
- chromosomes may have errors on the chromosome that can lead to new traits being expressed
Mutations
When DNA is damaged or changed so that the code carried by that gene is no longer the same (not all mutations can be seen/noticed and not all of them are bad)
-errors are detected by analyzing the Karyotype
Karyotype
- profile of organism’s chromosomes to diagnose genetic disorders
- a photographic inventory of an individuals chromosomes
- best photographed during late prophase or metaphase
- a Karyotype usually shows 22 pairs of autosomes and one pair of sex chromosomes
Autosomes
A chromosome that is not involved in determine the gender of an organism
-humans have 22 pairs of autosomes
Sex chromosome
- chromosome that determines the gender of an organism
- humans have one pair of sex chromosomes
- males: XY
- females: XX
Non-disjunction
Errors in meiosis occur when the chromosomes fail to separate properly. Results in gametes with more or less than the haploid number of chromosomes.
- meiosis I: homologous chromosomes fail to separate
- meiosis 2: sister chromatids fail to separate
Monosomy
- the loss of one chromosome
- having only one copy of a particular chromosome where there should be a homologous pair
- ie. Turner syndrome: missing X chromosome or posses an abnormal X chromosome
Trisomy
- the gain of one extra chromosome
- occurs when there are 3 chromosomes in place of one homologous pair
- ie. Down syndrome: extra chromosome #21
Non-disjunction of homologous chromosomes in meiosis I
Results in no normal cells produced, 2 with one extra chromosome and 2 with one missing one
Non-disjunction of sister chromatids in meiosis 2
Results in 2 normal cells and one with and extra chromosome and one missing one
Chromosomal Errors
- deletions
- duplications
- inversions
- translocations
Deletions
Sections of DNA are missing
Duplications
Sections of DNA are duplicated
Inversions
Sections of DNA are attached in reverse order
Translocations
Sections of DNA are reattached to the wrong chromosome (non-homologous)
Down Syndrome
- trisomy 21 (extra chromosome 21)
- developmental and intellectual disabilities
- 1 out of 800 live births
- chances increase with maternal age to 1/40 if mother is 40 or older
Turner Syndrome
- one X only (missing other X)
- 1 out of 2500 female live births
- do not reach sexual maturity
- fetuses tend to be miscarries before 20th week of pregnancy
Klinefelter Syndrome
- two X, one Y
- 1 out of 500 male live births
- usually sterile and exhibit some feminine body characteristics
Patau Syndrome
- trisomy of chromosome 13
- 1/25500 live births
- major developmental problems: brain, kidney and heart defects
- often only live a few months
Edwards Syndrome
- trisomy of chromosome 18
- 1/6000 live births
- most fetuses die before birth, otherwise tend to live less than a month
- many organ systems defective
Possible trisomy of chromosomes…
- 13, 15, 18, 21 and 22
- it is usually fatal if the embryo has trisomy of any of the other autosomal chromosomes
Name and describe a genetic disorder that can be diagnosed using Karyotyping
- Charcot-Marie-Tooth disease (CMT)
- caused by a duplication of chromosome 17
- leading to reduced muscle size, muscle weakness, and motor balance difficulties
Notation for Karyotyping
- # of chromosomes, gender, and extra or missing chromosome
- ie. 47, XXY
- ie. 47, XX, +21
