Inheritance and Variation Flashcards
Chromosomes- made of protein
chromosomes are present in the nuclei of all living cells. Each chromosome is composed of a single DNA molecule WRAPPED AROUND PROTEIN CALLED HISTONES.
dna molecules contain genteic information in the form of genes.
homologous pairs
chromosomes exist in homologous pairs, one of paternal and one of maternal origin.
22 pairs are chromosomes (which look alike)
1 pair is a sex chromosome
cell divison
when a cell divides, chromosomes with their genes are passed on to the new cells produced, known as daughter cells.
Two types of cell division
mitosis and meiosis
Mitosis
Mitosis occurs in all body cells except in the formation of gametes. During mitosis, two genetically identical cells are formed. Each cell contains the same number chromosomes as as the parent cell, i.e.
the diploid number 2n.
Importance of Mitosis
- It ensures that each daughter cell contains the diploid number of chromosomes. This maintains the
species number of chromosomes in all members of a species - It ensures that each daughter cell has an identical combination of genes.
- It is the method by which all cells of a multicellular organism’ are formed, hence it is essential for growth and to repair damaged tissues.
- It is the method used by organisms to reproduce asexually forming that ate identical to each other and the single parent
Clone
Since mitosis produces genetically identical cells, all offspring produced asexually from one parent are genetically identical and are collectively called clones.
Cloning
The process of making genetically identical organisms through non-sexual means.
Vegetative propagation
Some plants can reproduce asexuslly in certain structures of the parent plant a process known as vegetative propagation
Examples of NATURAL vegetative propagation
- New plants can grow from vegetative organs at the beginning of the growing season. Eg stem tubers and list out more
- New plants can grow from outgrowths of the parent plants such as leaf buds (BYROPHYLLUM PLANTLETS GROWS AT THE MARGIN) and RUNNERS (SAVANNAH GRASS GRASS IN UR YARD AND suckers
ARTIFICIAL Vegetative Propagation
By taking cuttings
Tissue culture
Cuttings
By taking cuttings, farmers and gardeners artificially propagate plants. Cuttings are parts of plants that
will develop roots and shoots to become new plants if given suitable conditions, e.g. stem cuttings
EXAMPLES
- When a piece of a sugar cane stem with two or three buds is placed horizontally on the soil, new
plants grow from each bud. - When a stem of hibiscus plant with a few leaves at the top is planted, roots grow from the cut end
forming a new plant.
Tissue culture
Tissue culture is used to artificially propagate plants, e.g. to propagate orchids, potatoes and
tomatoes. Small pieces of tissue called explants are taken from a parent plant and grown in a
nutrient-rich culture, under sterile conditions, to form cell masses known as calluses. Each callus is
then stimulated with appropriate plant hormones to grow into a new plant.
ARTIFICIAL VEGETATIVE PROPAGATION- bad and good
If cuttings or explants are taken from plants with desirable characteristics, e.g. a high yield, high
quality, resistance to disease or fast growth rate, then all plants produced will have the same desirable characteristics.
How to clone? (MAD SCIENTIST SH*T
To clone an animal, a nucleus is removed from an ovum of a female donor (ONE MOM) . A cell, still containing its
nucleus, is taken from the animal to be cloned and is fused with the ovum (SECOND MOM). This newly created ovum
is placed into a surrogate mother where it is stimulated to develop into an embryo (THIRD MOM). The surrogate
then gives birth to a new individual that is genetically identical to the animal from which the original
cell came, e.g. Dolly the sheep. A very low percentage of cloned embryos survive to birth, and animals born alive often have health problems or other abnormalities, and reduced life spans.
Meiosis
Meiosis occurs only in the reproductive organs during the production of gametes. During meiosis, four
genetically non-identical cells are formed. Each cell contains half the number of chromosomes as the
parent cell, known as the haploid number or n number.
Importance of meiosis
- IT ensures Each daughter cell has the haploid number of chromosomes. The diploid number can then be
restored at fertilisation. - Each daughter cell has a different combination of genes. This leads to VARIATION among offspring
which enables species to constantly change and adapt to changing environmental conditions
Heterozygous
Carrier
Homozygous dominant
Pure breeding
Homozygous recessive
Pure breeding
Albino/Albinism
Very pale skin that does not tan, white or light blond hair and very pale blue eyes nn
Normal pigmentation of hair skin and eyes NN Nn
In genetic diagrams
Include percentage, _ in 4 chance and ratio (simplify)
Co dominance
Neither allele dominates the other such that the influence of both alleles is visible in the heterozygous individual
Dominant trait
An inherited trait that results from the presence of a single dominant allele. It is seen in an individual with one or two dominant alleles
Recessive trait
An inherited trait that results from the presence of two identical recessive alleles. It is only seen in an individual with with no dominat allele
Example of co-dominance
In the IMPATIENS plant allele R stimulates red flowers allele W stimulates white flowers.
When an impatien plant with red flowers allele RR is crossed with a plant wit white flowers WW, neither allele is dominat over other and a pink flower is produced, RW is genotype
Sickle cell anaemia
Normal haemoglobin A
Abnormal allele stimulates the production of abnormal haemoglobin.
These alleles show co dominance Hb^A Hb^S
55-65% normal haemoglobin A
35-45%- abnormal haemoglobin S
Sickle cell anameia may develop in low oxygen conditions high altitude strenuous physical exercise
ABO blood groups
Controlled by three alleles I^A I^B I^O
A and B are both dominant to O
A and B are co-dominant
Only two alleles are present in any cell
E.g.
I^B I^O blood group is B
Pedigree charts
Used by genetic counsellors to identify potential risks for offspring developing a genetic disorder
- dominant (BOLDED and Capital letter)
- recessive (NOT BOLDED AND COMMON LETTER)
-female is a circle male is square
-horizontal line for marriage and sex
-vertical downwards for children/offspring
-if the PARENTS produce a child with that’s recessive AT LEAST ONE OF THEM MUST BE A CARRIER (Aa heterozygous)
-if it is unbolded recessive and therefore no dominant allele aa tt
-if they produce at least one offspring that’s a carrier or recessive they both have a recessive allele or heterozygous - only people people borne of people with the dominat trait and are dominant themselves are homozygous AND heterozygous
Sex linked characteristics
Characteristics determined by genes found on sex chromosomes only that have nothing to do with determining gender
EXAMPLE X^R
Sex determination
One pair is sex chromosomes.
XX genotype is women
XY is male.
Since the male is the only parent that can carry on the Y chromosome, males determine the sex of the offspring
Hemophilia
Sex linked condition in which blood fails to clot a cut.
In haemophilia and colour blindness only the x chromosomes carry the alleles. As a result males are more likely to have the condition as they only hv one X chromosome and if that one has a recessive trait they have the condition however since females have two X chromosomes BOTH MUST CARRY YHE RECESIVE ALLELE IN ORDER TO HAVE THE CONDITION
Variation
Continous AND Discontinous
NO two organisms are completely identical. PHENOTYPES all living organisms have thus EXPLAIN WHAT IT IS
Purebred
TT or tt
Hybrid
Heterozygous
Aa
Genetic causes of variation
Genetic variation arises in several ways:
Meiosis
Every gamete produced by meiosis has a different combination of genes as
result of:
- chromatids of homologous chromosomes crossing over and exchanging genes
-chromosomes arranging themselves around the equators of the spindles in totally random ways
Sexual Reproduction
**Mutations
Genetic variation occurs from SEXUAL REPRODUCTION
During fertilization , male and female gametes fuse in completely random ways to create different combinations of genes in each zygote.
Genetic mutation
A mutation is a sudden change in a single gene or in part of a chromosome containing several
genes. Mutations cause new characteristics to suddenly develop in organisms. Mutations occurring in
body cells cannot be inherited whereas mutations occurring in a gamete or zygote can be inherited.
Most mutations are harmful; however, a few produce beneficial characteristics which provide the
organism with a selective advantage in the struggle for survival, e.g . the peppered moth (see page 159).
Environmental causes of variation
Living organisms are constantly affected by the different factors in their environment.
Food, drugs,
physical forces, temperature and light can affect animals, Temperature, light intensity, availability of
mineral salts and water all affect plants. This variation is not caused by genes and cannot be passed on
to offspring
advantages of variation
- It enables species to adapt to changing environmental conditions, improving their chances of survival.
- It provides the raw material on which natural selection can work, and is therefore essential for
species to remain well adapted to their-environment or GRADYALLY CHANGE AND GET BETTER.
-It makes it less likely that any adverse changes in environmental conditions will wipe out an entire species since some organisms may be able to adapt to the new conditions
Continuous Variation
Continuous variation is where characteristics show a continuous gradation from one extreme to the other
without a break. Most organisms fall in the middle
of the range with fewer at the two extremes,.i.e. the
characteristics show a normal distribution.
Examples
include height, weight, foot size, hair colour, and leaf
size in plants.
Characteristics showing continuous variation are
usually controlled by many genes and can be affected
by environmental factors.
Discontinuous Variation
Discontinuous variation is where characteristics show clear cut differences with no intermediates.
Individuals can be divided into distinct categories, e.g. ABO blood groups, tongue rolling, and the
presence or absence_of horns in cattle.
Characteristics showing discontinuous variation are usually controlled by a single gene and environmental factors have little, if any, influence on them.
Speciation
The formation of new species.
As long as organisms from different groups within a species can interbreed and genes can flow
between them, the groups remain members of the same species. If groups become separated or
isolated, the flow of genes between them stops. Genetic differences gradually develop and a point is reached where members of the groups can no longer successfully interbreed. They become separate species, each with its own pool of genes
Speciation by geographical separation
This occurs when a physical barrier-prevents two groups of organisms of the same species from meeting and interbreeding. Such barriers include mountain ranges, deserts, oceans, rivers or
even streamS.
Speciation by ecological and behavioral separation
Speciation
can occur when two groups of organisms of the same species inhabit the same region
but they become adapted to different habitats in that region, which reduces-gene flow.
Behavioral
Speciation can also occur when animals exhibit elaborate courtship behaviours before mating,
which may be stimulated by the colour, markings, calls or actions of the opposite sex. If small
differences occur in any of these stimuli it can prevent mating, which prevents gene flow.
Extinction of species
Over time species can also become extinct, i.e. they no longer exist. Habitat loss, disease, predation
by introduced species, competition with introduced species or overexploitation by humans, e.g.
overfishing or overhunting, can all lead to extinction of species. For example, the Caribbean monk seal
has become extinct due to it being overhunted for its fur, meat and oil.
Natural selection
Natural selection is the process by which populations change over time or evolve, so that they remain well adapted to their environment.
THEORY OF Natural selection developed by charles darwin 1859
- Most organisms produce more offspring than are needed to replacethem, yet the numbers ofindividuals in populations remain relatively constant. In nature there must, therefore, be a constantstruggle for survival.
*All organisms show variation and much of this can be inherited. Those organisms possessingvariations that make themwell adapted to their environment are most likely to survive in thestruggle, i.e. there is survival of the fittest.
- Since the well adapted organisms are the most likely to survive, theyare the ones most likelyto reproduce, thereby passing on their advantageous characteristics to their offspring. Species,therefore, remain well adapted to their environment or they gradually change andimprovebybecoming even better adapted.
Natural selection preserves useful adaptations
The peppered moth
The peppered moth lives in Britain and is eaten by birds. Before the Industrial Revolution, the moths were black andwhite speckled and were well camouflaged against the pale
lichen-covered tree trunks on which they rested. During the Industrial Revolution, a melanic (all black) variety
appeared in the industrial area around Manchester. Thismelanic variety arose as a result of a dominant mutation and
was well camouflaged against the tree trunks which were
blackened with soot. This gave the melanic variety a selectiveadvantage in industrial areas and, over time, it became far
more numerous in these areas than the speckled variety.
Antibiotic and pesticide resistance
In natural populations of bacteria and various pests, e.g. insects, fungi and weeds, a few individualsmay carry genes that make themresistant to antibioticsor various pesticides, e.g. insecticides, fungicides and herbicides. These genes arise from mutations. When exposed to antibiotics orpesticides, these resistant organisms have a selective advantage;
they are more likely to survive and reproduce than non-resistant
organisms, passing on their resistance to their offspring. Thisis causing increasing numbers of resistant organisms to appear
within populations.
- Caribbean lizards
Anole lizards are thought to have colonised theislands of the Caribbean from Central and SouthAmerica. Through natural selection, lizards strandedon the four larger islands of Cuba, Hispaniola,
Jamaica and Puerto Rico independently evolvedinto different species with similar characteristics
that enabled them to fit similar ecological niches
on each island, e.g. twig anoles developed long, slender bodies and tails and short legs; trunk
ground anoles developed long, muscular legs, andcanopy anoles developed large toe pads. Today, the different species have equivalent species with
similar body types on each island.
Artificial selection
Artificial selection involves humans selectingandbreedingorganismsshowingdesirablecharacteristics. As a result, newbreeds, strains or varieties of plants and animals are produced with characteristics to suit human needs.
disadvantage of artifical selection
It has the disadvantage that it reduces variation in populations making them more vulnerable if environmental conditions change.
Inbreeding
Inbreeding involves breeding closely related individuals showing desirable characteristics. It is usually used to improve one particular trait. Continued inbreeding reduces the gene pool whichincreases the frequency of undesirable genes and reduces the overall fitness of the organisms. After several generations of inbreeding, outbreeding must take place to introduce new genes into a population
Outbreeding
Outbreeding involves breeding individuals from genetically distinct populations showing desirable characteristics. Offspring produced are called hybrids and usually show characteristics that are superior to both parents. This is known as hybrid vigour.
Artifical Selection in agriculture
- Increased yields, e.g. cattle that produce more milk or meat, chickens that lay more or larger eggs, sugar cane that produces more sucrose and cereal crops that produce more grain.
- Increased quality of product, e.g. meat with less fat, andcereals and ground provisions with a higher protein content.
- Faster growth rates.
- Increased number of offspring.
- Shorter time to reach maturity so that more generations are produced per year.
- Increased resistance to pests and disease. This reduces product loss and the need for pesticides.
- Increased suitability to the environment.
Artificial selection in the Caribbean
- Jamaica Hope, a breed of dairy cattle,the breed is heat tolerant, has a high resistance to ticks and tick borne diseases, and produces a high yield of milk, even when grazing on the poor pasturelands of the Caribbean.
- Sugar cane has been bred to produce varieties with a high sucrose content, increased resistance to disease and insect pests, greater suitability to its environment and improved ratooning ability.
Genetic engineering
Genetic engineering involves changing the traits of one organism by inserting genetic material from a different organism into its DNA. The organism receiving the genetic material is called atransgenicorganism or genetically modified organism (GMO).
Genetic engineering is used to:
- Protect agricultural crops against environmental threats, e.g. pathogens, pests, herbicides and low temperatures.
- Modify the quality of a product, e.g. increasing nutritional value.
- Make organisms produce materials that they do not usually produce, e.g. vaccines and drugs.
- Improve yields, e.g. increasing size or growth rate, or making organisms more hardy.
Golden rice
By inserting two genes into rice plants, one
from maize and one from a soil bacterium, theendosperm of the rice grains is stimulated toproduce beta-carotene which the body converts to vitamin A.
Golden rice should help fight
vitamin A deficiency which is a leading cause of blindness, and often death, of children in many underdeveloped countries.
Roundup resistant crops
By inserting a gene from a soil bacterium into certain crop plants, e.g. soya bean, corn and canola, the plants become resistant to theherbicide called ‘Roundup’. The herbicide can be sprayed on the crops to destroy weeds, but not harm the crops.
Bt corn
By inserting a gene from a soil bacterium into corn plants, the plants are stimulated to producea chemical that is toxic to corn-boring caterpillars. This makes the corn plantsresistant tothe caterpillars.
Genetic engineering and medical treatment
- Insulin
By transferring the gene that controls insulin production in humans into bacteria, the bacteria produce insulin which is used to treat diabetes. - Human growth hormone (HGH)
By transferring the gene controlling the production of HGH into bacteria, the bacteria produce the hormone which is used to treat growth disorders in children. - Hepatitis B vaccine
By transferring the gene controlling the production of hepatitis B antigens in the hepatitis B virusinto yeast, the yeast produces the antigens whichare used as a vaccine. Other drugs produced by genetic engineering include: - Blood clotting drugs for people with haemophilia.
- Follicle stimulating hormone (FSH) used to stimulate the ovaries to produce mature ova in women that are infertile
Advantages of genetic engineering
Some benefits of genetic engineering in agriculture are increased crop yields, reduced costs for food or drug production, reduced need for pesticides, enhanced nutrient composition and food quality, resistance to pests and disease, greater food security, and medical benefits to the world’s growing population.
disadvantages of genetic engineering
- Once a genetically modified organism is released into the environment, it cannot becontained orrecalled. Any negative effects are irreversible.
- The number of allergens in foods could be increased by transferring genes causing allergic reactions between species.
- unknown health risks may occur as a result of eating genetically modified plants andanimals.
- Large companies with funds and technology to develop genetically modified organisms could make large profits at the expense of smaller companies and poorer nations.
- *Difficult moral and ethical issues’
- Increased Weediness.
Other applications of gene technology
DNA testing or DNA fingerprinting
DNA testing involves analysing specific regions of DNA taken from cells of individuals
gene threpahy
Gene therapy
Gene therapy is an experimental technique that involves altering genes inside body cells to cure a disease or help the body fight a disease.
- By inserting a functional gene into cells to replace a defective gene that causes a disease.
- By inactivating or ‘turning off’ a defective gene that causes a disease.
- By introducing a gene into cells to help the body’s immune system tofight a disease.
