Genetics: Cells Flashcards
What are the three stages of the cell cycle in order?
Interphase, mitosis, cytokinesis
What stage of the cell cycle is the longest?
Interphase
What are the four phases of mitosis
Prophase, metaphase, anaphase, telophase
What 3 parts make up a nucleotide?
Deoxyribose sugar (pentagonal), phosphate group (circular), one of four nitrogenous bases (rectangular)
When nucleotides are linked together, what molecule is created?
Nucleic acids (DNA or RNA)
What shape is created when nucleotides link together?
Double-helix
Name the four nitrogenous bases used to create a DNA molecule
Purines: adenine, guanine
Pyramidines: thymine, cytosine
What is complimentary base pairing?
When two complimentary strands of DNA link up, adenine can only pair with thymine and guanine can only pair with cytosine because of their size and attraction
Describe the relationship between DNA, chromatin, chromosomes, genes, alleles, homologous chromosomes, and sister chromatids
DNA is the molecule that carries genetic instructions. Chromatin is the thin complex of DNA and proteins. Chromosomes are condensed structures made of chromatin. Genes are segments of DNA that code for a trait. Alleles are different versions of a gene. Homologous chromosomes are chromosome pairs. Sister chromatids are replicated copies of a chromosome
What are the two purposes of meiosis?
Genetic reduction: meiosis begins in diploid cells with the aim of producing haploid cells
Genetic recombination: creates sex cells that have a different combination of alleles by recombining the alleles in homologous chromosomes
What is crossing over?
Occurs in prophase I. Homologous chromosomes line up side-by-side in an alignment called synapsis, which forms a tetrad. They can then swap sections of genetic code between these chromosomes (genetic recombination). It can occur anywhere and in any amount among homologous pairs
What are the phases of meiosis?
Meiosis I: prophase I, metaphase I, anaphase I, telophase I
Meiosis II: prophase II, metaphase II, anaphase II, telophase II
Explain the difference between oogenesis and spermatogenesis
Oogenesis: meiosis in females. Begins before birth up to prophase I, then starting at puberty, one cell will complete meiosis each month until menopause. Takes a diploid oogonia and creates two polar bodies and one healthy egg cell. This is due to uneven distribution of cytoplasm
Spermatogenesis: meiosis in males. Takes a diploid spermatogonia cell and produces four haploid sperm. Begins at puberty and continues throughout life
What are some errors that can occur during crossing over?
Cri du Chat: deletion of a section of chromosome
Charcot-Marie-Tooth disease: duplication of a section of a chromosome (chromosomes 17 is longer, leading to low muscle definition, numbness, discoordination)
FG syndrome: inversion of a section of a chromosome (occurs only in males, leading to low muscle tones)
Chronic Myelogonous Leukemia: translocation of a section to a different chromosome (piece of chromosome 9 gets added to chromosome 22)
What is nondisjunction?
An error in the number of chromosomes, in which homologous chromosomes do not separate during anaphase I or when sister chromatids do not separate properly during anaphase II. The result is the production of sex cells that have either too few or too many chromosomes. Nondisjunction disorders increase with age, significantly in 40+ aged women
What is the name of the disorder that is Trisomy 21?
Down Syndrome
Describe prophase
No nucleus, chromatin condenses into visible chromosomes, centrioles move towards the poles and begin forming spindle fibres, nuclear membrane begins to disappear
Describe metaphase
Nuclear membrane completely dissolved, chromosomes line along the equator of the cell, spindle fibres attach to the centromeres of each chromosomes
Describe anaphase
Sister chromatids are pulled apart at the centromere towards opposite ends of the cell by the spindle fibres
Describe telophase
The chromosomes have reached the opposite ends of the cells, they start to unwind becoming less visible, nuclear membrane and nucleolus forms around each set
Describe interphase
Cells carry out their normal functions, grows, makes copies of its genetic material
What are the three stages of interphase?
G1, S-phase, G2
Describe the G1 stage of interphase
Major period of growth
Describe the S-phase of interphase
DNA (in its long, stringy form called chromatin at this time) is replicated
Describe the G2 stage of interphase
Further growth and molecule synthesis in preparation for mitosis, the cell is still carrying out its normal functions during all these phases
Describe cytokinesis in animal cells
Microfilaments constrict forming an indentation in the cell membrane along the equator of the cell. This eventually pinches off into two identical daughter cells, which are each back in G1 of interphase
Describe cytokinesis in plant cells
A new structure called a cell plate forms between the daughter nuclei. A cell wall forms on each side of the cell plate
Describe how DNA is replicated during interphase
The double-helix unwinds and each strand of DNA serves as a template for a new strand. Each new double-helix contains one original strand and one new strand
Describe meiosis I
One diploid cell is divided into two haploid cells
Describe prophase I
Homologous chromosomes line up side-by-side in an alignment called synapsis which forms a tetrad. They can then swap sections of the genetic code between these chromosomes (crossing over). This is where genetic recombination occurs
Describe metaphase I
Homologous chromosomes, which are paired in tetrads, line up together along the equator. Independent assortment occurs, in which the homologous chromosomes are pulled towards whichever pole they are closest to. The side they line up on is random. This alone can produce over 8 million different chromosome combinations
Describe anaphase I
The tetrads are pulled apart by spindle fibres towards the poles. One homologous chromosomes containing 2 sister chromatids moves to each end of the cell
Describe telophase I
The homologous chromosomes begin to uncoil and cytokinesis takes place forming two double-stranded haploid cells. Although the cells are haploid, they each contain chromosomes made of two sister chromatids attached at the centromere, so they can divide again
Describe meiosis II
Nearly identical to mitotic division except this division is haploid and mitosis is diploid. During this division, each of the two haploid cells from meiosis I will divide again to form a total of four haploid cells
Define chromosome
A long strand of DNA
Define gene
A section of a chromsome containing a sequence of DNA that codes for a trait and can be passed on to an offspring
Define allele
A different version of the same gene (Ex. One chromosome may have an allele for brown hair while another has an allele for blonde hair. They are both coding for the same gene of hair colour, but they are different forms of the gene)
How many chromosomes are in human body cells?
46
What is true about each homologous pair of chromosomes?
They contain genes for the same characteristics (Ex. Chromosome 1 contains, along with many others, the genes for blood protein and for a starch-digesting enzyme in saliva)
What are the sex chromosomes of a male and female?
Male: XY
Female: XX
What is the term for all other chromosomes except sex chromosomes?
Autosomes
Proteins are polymers made of units of what monomer?
Amino acids
How many different amino acids are there?
20
What is the term for three successive nucleotides?
Codon
How many codons code for one amino acid?
One
What is determined by the sequence of nucleotides?
What proteins to make, and thus, how to grow, develop, and function
Define genome
The complete sequence of DNA of an individual including all chromosomes
Define karyotype
A photograph of all the pairs of homologous chromosomes lined up
Describe cell theory
- All living things are made of one or more cells
- Cells are the smallest units of living organisms
- All cells come from pre-existing cells by cell division
What is the purpose of the cell cycle?
- Growth and repair of the organism
- Repair of tissues and organs
- Maintenance to replace dead cells
What is the term for a serious error in the mitotic process?
Mutation
Describe mutations
A permanent change or error in the DNA. They are passed down during mitosis to daughter cells, therefore they are localized groups of cells rather than in every cell in the body. They are caused by mutagens, toxic compounds, radiation, or viruses
When a sperm cell and an egg fuse together, what do they form?
Zygote
What is the human diploid number?
46
What is the human haploid number?
23
Define haploid
Having only one full set of chromosomes
Define diploid
Having two complete sets of chromosomes
Describe somatic cells
Diploid, each containing pairs of homologous chromosomes
Describe gametes
Haploid cells, each with half the number of chromosomes of their parent cells
Describe prenatal testing for nondisjunction disorders
When a pregnant woman has medical tests performed on the fetus to find information about possible physical and chromosomal anomalies. Tests include ultrasounds and amniocentesis, an invasive test, which carry risks with them
Review a diagram of mitosis
Review a diagram of meiosis
Review the shape and sequence of DNA strands
Give an example of a trisomy and monosomy
Trisomy: Trisomy 21 is Down Syndrome
Monosomy: Turner Syndrome is a female with only one X chromosome
