Mitosis, Meiosis & Inheritance Flashcards
- how many chromosomes are their in human cells
- what are autosomes, how many are there?
- in a chromosome, which is the p arm & which is the q arm?
- 46 or 23 pairs (23 from each parent)
- non sex chromosomes i.e non X or Y
- there are 22 pairs of autosomes
- p arm is the short arm (p for petite) & q arm is the long arm
How many DNA molecules in one chromosome?
Explain the differences between chromatid, chromosome & homologous chromosomes.
- 1 chromosome= 1 DNA molecule
- chromatid is one line (sometimes called a chromosome), chromosome is X (has two sister chromatids i.e identical chromatids), homologous are two Xs.
- what are telomeres?
- what is a metaphase spread?
- define homologous chromosomes.
- repeated sequences on the end of each chromosome.
- growth is arrested in metaphase, chromosomes are stained & can view banding patterns (a&t dark, c&g light)
- have same DNA sequence & same gene in them, may have different alleles (sister chromosomes are completely identical w same alleles but non sister chromatids have same genes w different alleles)
-what is mitosis, how many chromosomes at the start compared to end, what stage of the cell cycle does it happen?
- cell division for somatic cells, produces 2 identical daughter cells w 2n
- 46 at start & 46 at end (one round of replication, one round of division)
- M phase
Outline the steps of mitosis.
P-centrosomes separating, spindle fibres created, nuclear membrane disintegrating, chromosomes condense.
PM (prometaphase)- spindles connect, centrosomes move to poles in middle of the cell
M-condensed chromosomes line up in the middle at the metaphase plate
A-chromatids or separated to opposite poles of the cell. Still called chromosomes!
T-nuclear membrane redevelops, cleavage in middle of the cell ready to split into two identical daughter cells (2n)
What is meiotic nondisjunction?
- explain what happens if it takes place at the first post-zygotic division compared to a later post zygotic division
- define mosaicism
-where the chromosomes are not pulled apart correctly in anaphase leading to an unequal number of chromosomes in the granddaughter cell.
Earlier (meiosis I)= leads to all 4 granddaughter cells being affected w an abnormal chromosome number.
Later (meiosis II)= Meiosis I happens successfully, separating of chromosomes in meiosis II leads to 2 granddaughter cells being normal & 2 having trisomy and monosomy
-mosaicism= lineages of cells w different chromosome number eg an individual w Downs may have some cells that have 47 chromosomes & some w 46- caused by mitotic non disjunction
- what is meiosis ?
- how many chromosomes are there at the beginning & end ?
- special cell division for germline cells/ sex cells, one replication & 2 divisions
- produces for non-identical daughter cells (n) with half the chromosome content of the parental cell (2n)
Outline meiosis.
P1-centrosome separate, nuclear membrane disintegrates, homologous pairs find each other. this is where crossing over may take place- recombination, chiasmata
M1-homologous pairs lineup on the metaphase plate, form a tetrad *random assortment here, combos on how homologous chromosomes line up
A1-homologous pairs separate and are pulled to opposite poles of cell
T1- nuclear membrane appears daughter cells had 23 chromosomes in each nucleus(2n)
P2-chromosomes are condensed nuclear membrane and envelope disintegrate
M2-chromosomes line up in the middle of the cell at metaphase plate
A2-The chromatids are pulled apart
T2- The chromosomes are separated in two daughter cells with half the DNA content as parent cells.
What are some consequences of meiosis?
-how often does meiosis non disjunction happen?
- generation of genetic diversity via crossing over (prophase 1) & random assortment (metaphase 1)
- maintaining chromosome number through generations
- make & female meiosis (spermatogenesis & oogenesis)
- happens too often, causes 1/3 of all miscarriages, leading cause of mental retardation
Outline spermatogenesis.
- start w spermatogonium (2n), -> primary spermatocyte-> x4 spermatids-> x4 mature sperm
- from 1 spermatocyte (2n)to 4 sperm (n) in 60 days
Outline oogenesis.
- oogonium (2n) -> primary oocyte (2n) -> large egg (n) & polar bodies (n) -> mature ovum (n)
- happens in 12-50 years
Define: genotype, phenotype, gene, allele, homozygous, heterozygous, hemizygous, dominant, recessive, co-dominant.
- genetic make up
- physical characteristics
- The stretch of DNA sequence at a specific chromosomal location that carries the code for a polypeptide
- an alternative of a gene
- two alleles of a gene that are the same
- two alleles of a gene that are different
- only one allele of the gene on the X chromosome
- The dominant allele in a heterozygote determines the phenotype
- The non-dominant allele in a heterozygote is called recessive
- Neither allele in the heterozygote is dominant and the phenotype is new eg human ABO blood types
Give some key rules of pedigree analysis
- each generation on a separate line
- label every generation with room Roman numerals top to bottom
- siblings in age order from left to right
- label every individual of every generation left to right
- shading indicates phenotype
- half shading can indicate heterozygotes
Outline autosomal recessive inheritance
- heterozygous unaffected
- affected individuals are homozygotes recessive
- 2 affected individuals will only have affected offspring
- 2 heterozygotes have 25% chance of having affected offspring
- males and females equally affected
- disease seems to come out of nowhere and can skip generations
- both parents of affected individual are heterozygous carriers
Outlined autosomal dominant inheritance
- Heterozygotes affected
- autosomal dominant diseases are really found in him is like a state therefore assume that affected individuals are always heterozygous
- every affected individual has 50% chance of having affected offspring
- males and females equally affected
- every affected individual will have at least one affected parent
- disease cannot skip a generation
