Genetics (General) - Unit 2 Flashcards
Very briefly describe mitosis. What are the three purposes for mitosis?
- Asexual reproduction of cells involving a single parent producing identical daughter cells
- This is to create life, growth (more cells = more size), tissue repair
What are the two phases and subphases in the process of mitosis?
Interphase
- G1: Cell grows and performs normal functions
- Synthesis: DNA replications occurs
- G2: replication of organelles, prep for cell division
Mitosis
- Prophase
> Preparation
> Nuclear membrane and nucleolus disappear
> Spindle fibers form between each end of cell
> Centrioles move to cell poles, aster rays form around centrioles
> Chromatin condenses to form chromatids, forming chromosomes
> Each replicated copy of DNA is called a chromatid, 2 chromatid copies is one
- Metaphase
> Spindle fibers move chromosomes to center of cell
> Anaphase
> Spindle fibers separate chromatids into single chromosomes and pull to separate poles
- Telophase
> DNA returns to thin chromatin, nuclear membrane and nucleolus reappear, aster rays disappear in animal cells
- Cytokinesis
> Organelles in the cytoplasm divide, plant cells create cell plate, animal cells create cleavage furrow
What does DNA stand for? Briefly describe it’s function.
- DNA = Deoxyribose nucleic acid
- Contains all the information needed to keep an organism running
- Primary way to pass on hereditary information
Explain the basic structure of DNA.
- Consists of 2 molecules that are arranged into a ladder-like structure called a double helix
- Difference between the pentose sugar on RNA and DNA is the hydroxyl group on #2 carbon where DNA is missing an oxygen molecule
- Made up of millions of tiny subunits called nucleotides (can also makeup RNA)
- Each nucleotide consists of
- Phosphate group (circle)
- Pentose sugar (deoxyribose, ribose) (pentagon)
nitrogenous base (DNA rings) (rectangle) - Linked together by phosphodiester bonds between phosphate group of one nucleotide and sugar of another
- Sugar and phosphate groups alternate to form a sugar-phosphate backbone
- Backbone: sugar phosphate backbone, and nitrogenous base rungs
Name and explain the two types nitrogenous bases.
Purines 2 rings: adenine, guanine
Pyrimidines 1 ring: cytosine, thymine, uracil (in RNA)
Explain hydrogen bonds? What are the combinations of nitrogenous bases?
Two strands of DNA are held together by hydrogen bonds between nitrogenous bases, when bases join, they follow a pattern called complementary base pairing (purines and pyrimidines)
A+T = 2 hydrogen bonds
C+G= 3 hydrogen bonds
How do chromosomes form DNA?
Chromatin is winded tightly to form chromosomes, in the chromatin it is supercoiled, wrapping histones into the coils, creating nucleosomes, this unwinded creates double helix DNA
Give a detailed description of chromosomes.
- Made up of DNA that is organized into sections called genes
- Each gene controls a specific trait of an organism
- Each chromosome has different set of genes
- Genes have specific DNA sequences
- Somatic cells contain two of every chromosome- one from each parent
- This makes them diploid cells (2 chromosome)
- The genes on each part of chromosome code for the same info, but are not always identical, this makes them homologous
> ex. both code eye colour but one blue, one brown) - Humans have 22 pairs of somatic homologous chromosomes and one pair of sex chromosomes
- Since chromosomes are only visible during cell division, they are usually shown replicated with sister chromatids
- Each chromatid copy initially has identical information
- The information on each chromosome pair is similar but not identical
- Same sequence of genes code for the same trait
- Somatic cells have 46 chromosomes (23 pairs)
- In reproduction, male and female eggs and sperm keep the chromosome number from doubling in each succeeding generation
- Produced by cell division process, meiosis
- Gametes (sex cells) have only one of each kind of chromosome; these cells are said to be haploid (½)
- Meiosis is the cell division that occurs in sex organs to reduce the number of chromosomes from diploid to haploid by separating homologous pairs
- Spermatogenesis = sperm production
- Oogenesis = egg cell production
- Produces 4 cells from one parental cell, each have 23 individual chromosomes
What is an allele?
A different form of the same gene
> ex. brown eyes allele v. blue eyes allele
Explain the process of meiosis.
Prophase 1
- Chromosomes become visible
- Homologous chromosomes line up side by side, they undergo synapsis where they connect and pair up to form a tetrad
- DNA segments may be exchanged by crossing over
- This creates genetic variation
Metaphase 1
- Paired homologous chromosomes line up at the equator
- Pole they face is random, creating process called segregation or independent assortment
- This ensures genetic variation
Anaphase 1
- Homologous chromosome pairs separate to opposite poles, sister chromatids still attached
Telophase 1
- End up with 2 haploid cells, each cell has only one of each chromosome pair
Cytokinesis
- Cell divides into two cells, reduces resultant cells (23)
Interkinesis (Interphase II)
- Rest period, no DNA replication occurs
Prophase II
- Start of meiosis II
- Chromosomes do not pair
Metaphase II
- Lining up of chromosomes each with 2 sister chromatids
Anaphase II
- Chromatids separate and daughter chromosomes travel to poles
Telophase II
- Nuclear membrane begins to form around the chromatids, now they are individual chromosomes
- 4 haploid cells are produced (4 chromatids)
Why does meiosis occur?
- To produce sperm and egg
- This begins from germ cells which are specialized cells predestined to go through meiosis
- Fertilization is the process that creates diploid fertilized eggs called zygotes
How are gametes formed (two processes)?
Oogenesis
- Process of making haploid egg cells (oocytes)
- Begin in womb, in ovaries
- Progress until prophase 1 and pauses
- At puberty ‘paused’
- Oocytes continue to metaphase II and await fertilization
- Only one offspring because oogonium divides in oocyte then oocytes divide into polar bodies, only one egg is bred, all polar bodies die
- Polar bodies are unequal division of cytoplasm that result in smaller oocytes, still equal division of organelles but they die
- Goal is to produce a fortified egg that supports fertilization
Spermatogenesis
- Process of making haploid sperm cells (spermatocytes)
- Begins in male puberty
- Continuous process in testes
- 4 offspring
- Goal is to fertilize egg with speed and agility because few ovum
What are the five possible changes in chromosome structure?
Duplication: section appears twice in a row
Inversion: section is coded but inverted
Deletion: section is deleted
Insertion: section is inserted into another
Translocation: they code but in the wrong places
Give a brief description of chromosomal errors.
- Errors caused by changes in chromosome number during meiosis is called nondisjunction
- Either monosomy (loss of a chromosome) or trisomy (extra)
- Best spotted in metaphase because that is when chromosomes are lined up and visible along the equator
- Nondisjunctions happen during anaphase I or II where cells don’t separate properly (fail to separate or separate unevenly)
Why did Mendel use garden peas?
- Peas are easy to grow, producing a large number in short time
- Peas have distinct traits that are easy to detect
- Peas are self-fertilizing, the organs are enclosed by the flower, allowing Mendel to control how the peas reproduce
- Purebred: all offspring are identical to each other and parents
