❤️🔥3- inheritance Flashcards
genome
the entire set of the genetic material of an organism
each gene within a genome
is made up of a small section of DNA that codes for a particular sequence of amino acids- these sequences form different types of proteins
having two alleles the same is called
homozygous
having two alleles which are different are called
heterozygous
genes control
our characteristics as they code for proteins that play important roles in what our cells do
in the nucleus of a cell, the DNA
double helix supercoils to form structures called chromosomes- they are only visible through cell division
human body cells contain __ chromosomes
23 pairs of chromosomes
one chromosome from a pair is
inherited from each parent
each chromosome pair is called
a homologous pair
the 23rd pair of chromosomes are
the sex chromosomes
in females the sex chromosomes are
the same- a homozygous genotype (XX)
in males the sex chromosomes are
different- a heterozygous genotype (XY)
how many chromosomes do gametes contain
23 individual chromosomes
haploid
23 chromosomes
diploid
23 pairs of chromosomes
a gene is
a short length of DNA found on a chromosome that codes for a particular characteristic
alleles are
variations of the same gene- As we have two copies of each chromosome, we have two copies of each gene and therefore two alleles for each gene
One of the alleles is inherited from the mother and the other from the father
This means that the alleles do not have to ‘say’ the same thing
alleles can be
dominant or recessive- A dominant allele only needs to be inherited from one parent in order for the characteristic to show up in the phenotype
A recessive allele needs to be inherited from both parents in order for the characteristic to show up in the phenotype.
If there is only one recessive allele, it will remain hidden and the dominant characteristic will show
gamete
sex cells
chromosome
threads which carry genetic information in the form of genes- located in the nucleus of cells
gene
short lengths of DNA found on chromosomes which code for specific proteins
allele
alleles are different versions of a particular gene
dominant
a dominant allele is always expressed, even if only one copy is present
recessive
a recessive allele is only expressed if two copies are present (therefore no dominant allele present)
homozygous
if two alleles of a gene are the same
heterozygous
if two alleles of a gene are different
genotype
the combination of alleles that control each characteristic
phenotype
the observable characteristics of an organism
who is responsible for determining the sex of a child
the male as only he has a Y chromosome
characteristics which are controlled by more then one gene are described as
polygenic
mitosis is used for
growth, repair of damaged tissues, replacement of cells and asexual reproduction
process of mitosis
Just before mitosis, each chromosome in the nucleus copies itself exactly (forms x-shaped chromosomes)
Chromosomes line up along the centre of the cell where cell fibers pull them apart
The cell divides into two; each new cell has a copy of each of the chromosomes
importance of mitosis
All cells in the body (excluding gametes) are produced by mitosis of the zygote
Mitosis is important for replacing cells e.g, skin cells, red blood cells and for allowing growth (production of new cells e.g. when a zygote divides to form an embryo)
mitosis
Mitosis is cell division which produces two identical diploid cells for growth and repair
meiosis
Meiosis is the type of cell division that produces gamete
when gametes are formed chromosomes must be
halved - otherwise there would be double the number of chromosomes after they join at fertilisation in the zygote
when does the halving of chromosomes occur
during meiosis, as so it is described as a reduction division in which the chromosome number is halved from diploid to haploid, resulting in genetically different cells
process of meiosis
Each chromosome makes identical copies of itself (forming X-shaped chromosomes)
First division: chromosomes pair up along the centre of the cell, recombination occurs and then cell fibres will pull the pairs apart, each new cell will have one of each recombinant chromosome pair
Second division: chromosomes will line up along the centre of the cell, cell fibres will pull them apart (as with mitosis)
A total of four haploid daughter cells will be produced
importance of meiosis
Production of gametes e.g. sperm cells and egg cells, pollen grains and ovum
Increases genetic variation of offspring
Meiosis produces variation by forming new combinations of maternal and paternal chromosomes every time a gamete is made, meaning that when gametes fuse randomly at fertilisation, each offspring will be different from any others
features of mitosis
two daughter cells produced, daughter cells are diploid, daughter cells are genetically identical to each other and to the parent cell, one cell division occurs
features of meiosis
four daughter cells produced, daughter cells are haploid, daughter cells are genetically different from each other and the parent cell, two cell divisions occur
variation
differences between individuals of the same species
variation can be dividing into two types depending on
how you are able to group the measurements
two types of variation
-Continuous variation is when there are very many small degrees of difference for a particular characteristic between individuals and they are arranged in order and can usually be measured on a scale
Examples include height, mass, finger length etc. where there can be many ‘in-between groups
-Discontinuous variation is when there are distinct differences for a characteristic
For example, people are either blood group A, B, AB or O; are either male or female; can either roll their tongue or not - there are no ‘in-betweens’
phenotypic variation can be caused in two main ways:
environmental- caused entirely by the environment in which the organism lives
genetic- controlled entirely by genes
meiosis creates
genetic variation between the gametes produced by an individual - this means each gamete carries substantially different alleles
during fertilisation any
male gamete can fuse with any female gamete to form a zygote - this random fusion of gametes at fertilisation creates genetic variation between zygotes as each will have a unique combination of alleles
characteristics of all species can be affected by environmental factors such as
climate, diet, accidents, culture and lifestyle
discontinuous variation is usually caused by
genetic variation alone
mutations are
rare, random changes that occur in the sequence of DNA bases in a gene or a chromosome
mutations occur
continuously
mutations in a gene can lead to
a change in the protein that the gene codes for
most mutations don’t alter the protein or
only alter it slightly so that its appearance or function isn’t changed
an insertion mutation
changes the amino acid that would have been coded for by the group of three bases in which the mutation occurs
an insertion mutation also has a knock on
effect by changing the groups of three bases further on in the DNA sequence
a deletion mutation
changes the amino acid that would have been coded for by the group of three bases in which mutation occurs
a deletion mutation has a knock on
effect by changing the groups of three bases further on in the DNA sequence
a substitution mutation
will only change the amino acid for the group of three bases in which the mutation occurs- it will not have a knock on effect
evolution is
the change in the frequency of a phenotype in a population over many generations
Darwins theory
Individuals in a species show a wide range of variation caused by differences in genes
Individuals with characteristics most suited to the environment have a higher chance of survival and more chances to reproduce
Therefore these characteristics are passed to their offspring at a higher rate than those with characteristics less suited to survival
Over many generations, these beneficial characteristics become more common in the population and the species changes (the species evolves)
antibiotics are
chemical substances made by certain fungi or bacteria that affect the working of bacterial cells either by disrupting their structure or function or by preventing them from reproducing
antibodies are effective
against bacteria but not against viruses
antibiotics target processes and structures that are
specific to bacteria cells- as such they do not generally harm animal cells
antibiotics have been
overused and antibiotic resistance has developed in many different types of bacterial species
bacteria resistance to antibiotics
Bacteria, like all organisms, have random mutations in their DNA
One of these mutations may give them resistance to an antibiotic
If an organism is infected with bacteria and some of them have resistance, they are likely to survive treatment with antibiotics
The population of the resistant bacteria will increase
If the resistant strain is causing a serious infection then another antibiotic will be needed
A strain of Staphylococcus aureus has developed resistance to a powerful antibiotic methicillin, this is known as MRSA (Methicillin resistant Staphylococcus aureus)
MRSA can infect wounds and is difficult to treat without antibiotics
preventing resistant bacteria
Doctors need to avoid the overuse of antibiotics, prescribing them only when needed – they may test the bacteria first to make sure that they prescribe the correct antibiotic
Antibiotics shouldn’t be used in non-serious infections that the immune system will ‘clear up’
Antibiotics shouldn’t be used for viral infections
Patients need to finish the whole course of antibiotics so that all the bacteria are killed and none are left to mutate to resistant strains
Antibiotics use should be reduced in industries such as agriculture – controls are now in place to limit their use in farming
reducing the spread of resistant strains of bacteria
Good hygiene practices such as handwashing and the use of hand sanitisers have reduced the rates of resistant strains of bacteria, such as MRSA, in hospitals
The isolation of infected patients to prevent the spread of resistant strains, in particular in surgical wards where MRSA can infect surgical wounds
antibiotics do not affect viruses-
Viruses cannot be treated with antibiotics
This is because antibiotics work by disrupting cell functions such as respiration, or breaking down the structure of the cell in some way
However, viruses do not carry out any cell functions and do not have cell walls, cell membranes or any cell organelles as viruses infect and utilise the machinery of animal cells to reproduce, which are not affected by antibiotics.
Therefore the action of antibiotics do not affect them
