Biology - inheritance Flashcards
how are gametes made
by cell division (meiosis)
what type of cells does meiosis produce
non- identical cells ( every sperm cell and egg cell are different )
what is fertilisation
The fusing of the egg and sperm to create a zygote
what is asexual reproduction
- reproduction that only requires one parent because there is no mixing of genetic information
- the cells divide by mitosis and the offspring are genetically identical (clones) of the parent
- ## asexual reproduction doesn’t involve gametes
what is sexual reproduction
requiring a male and female sex cell, the gametes fuse together to form a zygote, which develops to form offspring genetically different to both parents
(there is mixing of genetic information which leads to variation in the offspring.)
what is formed as a result of meiosis
4 gametes that are all genetically different from each other
what does haploid mean
has a single set of chromosomes, half the amount of normal body cells
what does diploid mean
having both sets of chromosomes, the correct number for normal body cells
where does meiosis take place
ONLY IN REPRODUCTIVE ORGANS ( testes in men and ovaries in females )
what are the stages of meiosis
- chromosome pairs line up along the cell equator
- the pair of chromosomes are separated and move to opposite poles of the cell ( the side to which each chromosome is pulled is random, creating variation
- chromosome number is halved
- chromosomes line up along the cell equator
- the chromatids are separated and move to opposite poles
- 4 unique haploids gametes are produced
describe fertilisation and the resulting outcome
- gametes join together to restore the normal number of chromosomes, and the new cell then divides by mitosis ( which increases the number of cells)
as the embryo develops , cells differentiate forming different cell types
why is meiosis important for sexual reproduction
- increases genetic variation
- ensures that the zygote formed at fertilisation is diploid
what are advantages of sexual reproduction
- the offspring receive a mixture of genetic information from two parents = produces variation in the offspring = if there are any changes in the environment then this variation = that some of the offspring may survive ( survival advantage by natural selection )
- natural selection can be speeded up by humans in selective breeding to increase food production. = high yield
what are the advantages of asexual reproduction
-only one parent needed
-more time and energy efficient as do not need to find a mate
-faster than sexual reproduction
- many identical offspring can be produced when conditions are favourable.
disadvantage of sexual reproduction
- two parents are required. this makes reproduction difficult in endangered populations
- more time and energy are required so fewer offspring are produced
disadvantages of asexual reproduction
- because all the offspring are genetically identical there is a risk they could all die if conditions become unfavourable
how do malarial parasites reproduce
reproduce asexually in the human host BUT reproduce sexually in the mosquito
how do fungi reproduce
Many fungi reproduce asexually by spores but also reproduce sexually to give variation.
how do plants reproduce
Many plants produce seeds sexually but also reproduce asexually by runners such as strawberry plants, or bulb division such as daffodils.
where are chromosomes found
in the nucleus of the cell
what molecule do chromosomes contain
DNA
what is DNA
DNA is a polymer made up of two strands forming a double helix. The DNA is contained in structures called chromosomes.
what is a gene
small section of DNA on a chromosome
what is a genome
The genome of an organism is the entire genetic material of that organism
what is the importance of understanding the human genome
- search for genes linked to different types of disease
- understanding and treatment of inherited disorders
- use in tracing human migration patterns from the past eg can help to find ancestry
describe the structure of DNA
-DNA is made up of 2 strands that twist around to form a double helix structure
- made from four different nucleotides.
- Each nucleotide consists of a common sugar and phosphate group with one of four different bases attached to the sugar. DNA contains four bases with complementary base pairs : A = T, C = G
how does the order of bases matter
The order of bases controls the order in which amino acids are assembled to produce a particular protein.
describe the stages of protein synthesis
1st stage ( transcription ) : takes place in the nucleus
- the base sequence of the gene is copied into a complementary template molecule ( this template messenger = mRNA ( mRNA = single-stranded molecule)
-MRNA passes out of the nucleus and into the cytoplasm
2nd stage ( translation ): takes place in cytoplasm
- mRNA molecule attaches to a ribosome
- amino acids are now brought to the ribosome on carrier molecules ( tRNA)
- ribosome reads the triplets of bases on mRNA and uses this to join together the correct amino acids in the correct order
- once the protein shape is complete it folds into its unique shape , the shape enables the protein to do its job.
what are proteins
polymers of amino acids
what is a chromosome
long, coiled molecule of DNA that carries genetic material in the form of genes
how many chromosomes does a normal human body cell have
46 ( 23 pairs )
how many chromosomes does a normal human gamete have
23
how do nucleotides interact to form a molecule of DNA
sugar and phosphate join to form a sugar-phosphate backbone in each DNA strand
base connected to each sugar
complementary base pair joined by weak hydrogen bonds
how does a gene code for a protein
- a sequence of three bases in a gene form a triplet
- each triplet codes for an amino acid
- the order of amino acids determines the structure and function of protein formed
what does the specific order of the amino acids determine
the shape of the protein
what does the shape of the protein determine
determines the protein’s function
what are examples of proteins
amylase ( enzyme protein )
collagen ( structural protein )
insulin ( hormone protein )
what is the order of amino acids determined by
the sequence of bases in the gene for a protein
what is a mutation
a change to a base
what are non - coding regions of DNA
regions that can be switched on or off ( regions tell genes when to produce proteins )
what happens if there is a mutation in non - coding regionss
affects how genes are switched on and off therefore may produce a protein that is not meant to have at that time which can cause uncontrolled mitosis = cancer
what are alleles
versions of gene
what is a genotype
the alleles present regarding a particular characteristic
what does homozygous mean
a genotype with two identical alleles
what does heterozygous mean
a genotype with different alleles for a characteristic
what is the phenotype
the physical appearance of a particular characteristic, coded for by the genotype
what is a dominant allele
the allele that is always expressed in a genotype, even if there is only one present
what is a recessive allele
the allele that is only expressed if two copies are present, and there is no dominant
what is cystic fibrosis
a disorder of cell membranes is caused by a recessive allele.
what is polydactyly
having extra fingers or toes and is caused by a dominant allele.
how are embryos screened for inherited disorders
- During IVF, one cell is removed ( from an 8-cell embryo ) and tested for disorder-causing alleles. if the cell doesnt have any indicator alleles, then the originating embryo is implanted into the uterus
disadvantages of embryo screening
- can give a false positive/negative result, which can lead to unnecessary terminations or births of children with unexpected genetic conditions
- screening is expensive
-concerns arise that screening gives rise to demand for ‘designer babies’ that parents choose solely based on sex, looks, or intelligence
- large number of embryos are created but only small numbers are implanted = some healthy embryos are destroyed = unethical
what is gene therapy
where faulty alleles can be corrected and be used to treat inherited disorders
how many chromosome pairs contain the genes which determine inherited characteristics ONLY
22 but only 1 pair contains the gene that determines sex
what is the male sex chromosome
XY
what is the female sex chromosome
XX
what type of substance does a gene code for
a certain protein molecule
what are the monomers of DNA
nucleotides
what are DNA nucleotides made up of
- common sugar
- phosphate group
- one of 4 bases
why is the ‘ folding of amino acids important in proteins such as enzymes
the folding of amino acids determines the shape of the active site which must be complimentary to the shape of the substrate
describe the effect of a gene mutation in coding DNA
- if a mutation changes the amino acid sequence , protein structure and function may change ( an enzyme may no longer fit its substrate binding site or a structural protein may lose its strength )
- if a mutation doesn’t change amino acid sequence, there is no effect on protein structure or function
what is non coding DNA
DNA which does not code for a protein but instrad controls gene expression
what are the economic issues concerning embryo screening
- Cost of hospital treatment and medication will need t be considered if it is known that a child will have an inherited disorder and financial support may be needed
what is the problem with single gene crosses
most characteristics are controlled by multiple alleles rather than just one
