Ch13 Reproduction Flashcards
asexual reproduction basics
involves one parent
cells divide by mitosis
no variation in offspring- genetically identical clones
sexual reproduction
involves male sex cell and female sex cell
the two gametes fuse to form a zygote
offspring have variation due to mixing of genetic info
Formation of gametes
meiosis
How does meiosis work
The genetic information of a cell is copied into four sets
Each chromosome forms a pair of chromatids
The cell then divides twice in succession to form 4 gametes
each has a single set of chromosomes(the chromosome number is reduced by half- 23)
Each gamete produced is genetically unique
gametes
organism’s reproductive cells
Fertilisation
When the two gametes fuse during fertilisation, it restores the normal number of chromosomes
(23+23=46)
The combination of genes in each fertilised egg is unique(variation)
The fertilised egg then divides by mitosis, increasing number of cells rapidly
As embryo develops, the cells differentiate
haploid
23 chromosomes within a cell
diploid
46 chromosomes within a cell
Asexual fungi reproduction
common reproduction is asexual by spores
e.g. toadstools, puffballs and mould
Sexual fungi reproduction
when conditions aren’t good to give variation for survival advantage
two hyphae from different fungi join and the nuclei fuse to create new hyphae with two sets of chromosomes
it undergoes meiosis to make haploid spores which are different from original hyphae
spores produce fungi better adapted to survive
hyphae
mass of thin threads that make up fungi
sexual plant reproduction
the gametes pollen(male) and egg cells(female) are produced using meiosis
asexual plant reproduction
e.g. strawberry plants, spider plants and the divisions of bulbs in daffodils
asexual malaria parasites reproduction
only happens in human liver and blood cells
sexual malaria parasites reproduction
inside mosquito red blood cells
when mosquito takes her blood meal, the drop in temperature between human body and mosquito triggers sexual reproduction in parasites
20 minute window when sexual forms develop and bursts out of blood cells
sexual forms fuse to form zygote with 2 sets of chromosomes(variation)
zygotes undergo meiosis to produce new asexual parasites
genome of an organism
the entire genetic material of that
organism
e.g. chromosomes and mitochondria genetic info
mitochondria dna
always inherited from the mother(comes form the egg)
DNA
long polymer molecule made up of repeating nucleotide units
they twist and spiral to form a double helix
nucleotide
common sugar
phosphate group
either 4 different bases attached to the sugar
base groups
A with T on the opposite strand
G with C on the opposite strand
Nucleotides grouped into 3 bases
sequence of the three bases code for a particular amino acid
order of the bases controls the order in which amino acids are assembled to produce a particular protein
Importance of understanding the human genome
search for genes linked to different types of disease
- able to predict risk for each individual
understanding and treatment of inherited disorders
- e.g. cystic fibrosis and sickle cell disease
use in tracing human migration patterns from the past
- understanding human evolution
protein synthesis
- genes in DNA -produce a template for the proteins by reflecting the sequence of bases in the DNA
- template leaves nucleus through pores in the nuclear membrane and binds to the surface of a ribosome
- cytoplasm contains carries molecules, each attached to a specific amino acid.
- The carrier molecules attach themselves to the template in the order given by the DNA
- the amino acids are joined together to form a certain protein
- this process occurs until the template is completed
- protein detaches from the carrier molecules and the carrier molecules detach from the template and return to the cytoplasm
- protein then folds to create unique shape to carry out it’s job function e.g. structural protein it will form fibrous structures like collagen
Gene expression
the process by which specific genes are activated to produce a required protein
non-coding parts of DNA
determines how much of gene is switched on or off
variation in non-coding parts affect how genes are expressed
mutations in coding part of DNA
changes in existing genes - most don’t alter protein formed
sometimes alters protein formed to give it a different shape
e. g. enzyme active site no longer fits substrate
e. g. structural protein loses its strength
may give an advantage
e. g. more efficient enzyme
e. g. stronger structural protein
mutations in non-coding part of DNA
can affect which genes are switched on or off(expressed)
- have big effect on phenotype
allele
different versions of the same gene
each one codes for a different protein
gene
small section of DNA on a chromosome
each gene codes for a particular sequence of amino acids, to make a specific protein
dominant allele
always expressed in the phenotype even when they are only present in one of the chromosomes
recessive allele
only expressed in the phenotype if they are present on both chromosomes(no dominant alleles present)
phenotype
the physical appearance or biochemistry of an organism regarding a particular characteristic
e.g. black fur or blue eyes
genotype
the genetic arrangement(collection of alleles) that determines the traits that an organism inherited from its parents
e.g. Bb
homozygous
alleles are both identical for the same characteristic
AA or aa
homozygote- individual who has two identical alleles for a particular gene
heterozygous
alleles are both different for the same characteristic
Aa
heterozygote- individual who has different alleles for a particular gene
Cystic fibrosis
inherited disorder of cell membranes prevents movement of certain substances from one side to the other mucus becomes thick and sticky organs become clogged caused by recessive allele
polydactyl
inherited disorder - having extra fingers or toes
caused by dominant allele
Embryo screening types
Amniocentesis
- taking some fluid from around developing foetus which contains foetal cells
Chorionic villus sampling of embryonic cells
- taking a sample of tissue from developing placenta
Embryo screening disadvantages
- increase risk of miscarriage(even if foetus is healthy)
- can give false positive or negatives
- hard decision for parents- emotional turmoil
- expensive
- everyone should have the tests(costly for society to provide healthcare for child affected by genetic disorder) - ethical - could give rise to demand for ‘designer babies’
- no cure
