Genetics Flashcards
Genes
units of DNA coding for a particular piece of information
Chromosomes
segments of DNA which also contain proteins
Cell cycle
- contains interphase and division
Interphase
- G1: cell makes components that allows the cell to divide to make two identical cells
- S: DNA is synthesised as each cell has to have its own copy of genetic material
- G2: cell continues to grow
Prophase
- chromosomes condense
- each chromosome made from 2 chromatids joined at a region called the centromere
Telomere
- region at the end of a chromosome
- protects chromosome from damage
Metaphase
- chromosomes line up along the metaphase plate of the cell as a spindle has formed
- fibres extend down from opposite poles to the middle of the cell and grab hold of the centromere
- spindle fibres attach to the kinetochore
Kinetochore
- complex of proteins surrounding the centromere
- where spindle fibres attach to
Spindle fibres
- forms of proteins called microtubules
- initiated from opposite poles of the cell
Anaphase
- once spindle fibres attach to kinetochore, microtubules contract and pulls them apart to opposite sides
Telophase
- 2 nuclei are produced
- 2 daughter cells are formed
Meiosis
Meiosis I
- each chromosome is replicated so sister chromatids are formed
- homologous chromosomes form bivelant with each other
- spindles form, attach to centromeres, pull chromosomes apart
Meiosis II
- starts with 2 products which have one copy of each chromosome
- spindle fibres form and attach to centromere
fibres shorten and pull apart chromatids
- 4 haploid products are formed
Diplotene
- stage during Prophase I
- there are regions within bivelants where sister chromatids interact
- parts of sister chromatids break and rejoin by crossing over
- forms chiasma
Independent assortment
- allows different products to be formed from different combinations of chromosomes
- bivelants assort independently
Wild-type
common form of a character (normal)
Mutant
rare form of a character (affected)
Homozygous
2 identical alleles
Heterozygous
2 different alleles
Phenotype
the appearance controlled by combination of alleles
Dominant inheritance
if an affected individual has an affected parent
Test cross
used to determine genotype of an individual who is showing the dominant feature phenotype
Pleitropy
a single gene mutation influences multiple phenotypes and characteristics
Expressivity
variation in degree to which the phenotype is shown
Penetrance
individual in one generation can have the mutant genotype, but do not express the phenotype
Incomplete dominance
- form of inheritance where one allele for a specific trait is not completely expressed over its paired allele
- results in third phenotype which physical trait is a combination of both
Complete dominance
- form of dominance in heterozygotes
- allele regarded as dominant completely overrides effect of allele that is recessive
Sex linked chromosomes
genes on the X chromosome are said to be sex linked
Epistasis
interaction of phenotypes controlled by different genes, but affect the same character
Complementation test
- genetic experiment that indicates whether two mutations affect one gene or two different genes
- one gene = no complementation
- two genes = complementation
Pseudo-autosomal region
- regions at each end of the Y chromosome, which allow it to align with the X chromosome
SRY gene
- determines male development
Aneuploidy
- when there is an abnormal number of chromosomes
- eg. down syndrome has 47 chromosomes as there are 3 copies of chromosome 21
1 copy - monosomy
2 copies - disomy
3 copies - trisomy
4 copies - tetrasomy
Trisomy
- results in death in other chromosomes apart from 13, 18 and 21
- occurs through problem in meiosis
- non-dysjunction is failure to separate either homologous chromosomes or sister chromatids
Barr bodies
dark staining region representing inactive x chromosome
X chromosome inactivation
- known as dosage compensation
- prevents females having too much of same gene expressed
- one copy of each gene is switched off in either chromosome
Polyploids
- organisms with extra copy of chromosomes
- fatal in humans, acceptable in plants
- results in larger appearance
Mutations
occur when DNA sequence is changed
Epigenetics
study of change in activity of genes that do not result from changes in DNA sequence
Genomic imprinting
- expression of different genes is determines by with parent it is inherited from
- imprint is erased in germline cells
- imprint is maintained in somatic cells
Epigenetic mark
mechanism that switches off X chromosome
Cell autonomous phenotype
- determined by the genotype of the cell it has formed from
- only cells with mutant genotype show mutant phenotype
Cell non-autonomous phenotype
- cells can show mutant phenotype regardless of their genotype
Hardy Weinberg equilibrium
- no change in allele frequency from one generation to another
p2 + 2pq + q2 = 1
Hardy Weinberg true if:
- there is random mating there is no selection - there is no migration - there is no mutation - population is large
Anisogamy
gametes differ in size
Hermaphroditism
- organism has both male and female gametes
- favoured if mate searching efficiency is low
