selective breeding Flashcards
genome
the sum total of genes in an organism
phenotype
the observable characteristics of an organism. depends on a genotype and environment
genotype
the alleles present in an organism
locus
position on a homologous chromosome of a particular gene
homologous chromosome
a pair of chromosomes that have the same gene loci but not necessarily the same allele
allele
alternative form of a gene
gene
length of DNA that codes for a polypeptide
gene pool
Total number of all alleles of all genes of al individuals within a particular population at a given time
population
all the organisms of one species in a habitat
species
A group of similar organisms that can interbreed to produce fertile offspring
dominant allele
the allele which exerts an affect on the phentoype of the heterozygote
recessive allele
The allele which has no effect on the phenotype of the heterozygote
co-dominant allele
When both alleles exert an effect on the phenotype of the heterozygote
gamete
a sex cell e.g. sperm or ovum
zygote
the fertilised female gamete
homozygous
A genotype in which the 2 alleles of a gene are the same
heterozygous
A genotype in which the 2 alleles of a gene are different
haploid
Cells containing one full set of chromosomes
diploid
Cells containing two full set of chromosomes
what is variation?
difference that exists between individuals.
variation between species and within species
variation between species
Different species have different genes which results in different phenotypes
variation with A species
Individuals of the same species have the same genes but different alleles (version of gene)
what is genetic diversity
Genetic diversity is the “total number of different alleles in a population”
what causes variation in a species?
genetic and environmental factors
genetic factors causing variation?
Mutations
Meiosis (crossing over and independent assortment)
Random fertilisation of gametes
equation for genetic and environmental contributions
VP = VG + VE
VP is phenotypic variation
VG is the genetic component
VE is the environmental component
qualitative differences?
Fall into clearly distinguishable categories with no intermediates
e.g. different blood groups
This is discontinuous variation
quantitative differences
do not fall into clearly distinguishable categories
e.g. height in humans
This is continuous variation
what happens if variation is mainly due to genetic factors
then organisms fit into a few distinct forms with no intermediates as it is usually controlled by a single gene
what occurs if variation is mainly due to environmental factors?
then organisms don’t fit into distinct forms & have many intermediates as it is usually controlled by a many gene (polygenes)
what is the definition of selective breeding?
“The production of desired changes in the phenotype of an organism by artificially selecting as parents those individuals which show the desired phenotype to a larger degree than other individuals”
what does selective breeding cause?
- changes in phenotype
- changes in allele frequency
what changes in allele frequency occur?
- increase in desired allele
- decrease in non desired allele
examples of general aims of selective breeding
- increase yield of crops
- increase animal performance (racehorses etc.)
- produce pest resistant/disease resistant variations of farm animals/crops
- produce particular characteristics/phenotypes in pets
what are the male parts of plants?
stamen, which includes:
- Anther
- filaments
what are the female parts of plants?
carpel which includes:
- stigma
- style
- ovary
- ovules
which part of the plant produces the male gametes?
anther
during fertilisation the pollen grains are transferred to what part of the plant and how is this achieved?
Anther (on the stamen) to the stigma.
wind, water, insects or animals
what is the function of the endosperm?
provides nourishment to the embryo
What is meant by the term “inbreeding depression”?
- reduction in size/yield/vigout/fertility
- occurs when “natural out breeders” are repeatedly inbred
What is meant by the term “hybrid vigour”?
- An offspring hybrid that has a greater yield and more vigorous growth than either parent – often occurs when crossing natural outbreeders
What does selective breeding depend on?
choosing as parents individuals who owe their desirable phenotype to their genotype and not to their environment
What is heritability?
the proportion of phenotypic variation that is genetic
what does successful selective breeding require?
high heritability
what is the range of heritability values and what do they mean?
0 (no genetic contribution) and 1 (no environmental effect)
what do heritability values of less than 0.02 mean?
that selective breeding will have little effect
what is natural selection?
a process resulting in the survival of those individuals from a population of animals or plants that are best adapted to the prevailing environmental conditions. The survivors tend will tend to survive and reproduce in greater numbers than others of their kind, thus ensuring the perpetuation of those favorable alleles/ traits in succeeding.
what is artificial selection?
Modification of a species by human intervention, such as breeding, so that certain desirable alleles/ traits are represented in successive generations.
The different breeds of cows and domestic dogs are products of artificial selection.
ways of selective breeding a plant?
- traditional
- marker assisted breeding
- transgenic technology
- gene editing
what techniques are used in selective breeding for animals?
- artificial insemination
- cloning and embryo transplantation
- progeny testing
- cloning by somatic cell nuclear transfer
- in vitro fertilisation
what problems are encountered with traditional animal selective breeding techniques?
- size (mammals are large)
- time taken to reach sexual maturity
- long gestation period
- produce a small number of offspring
what is progeny testing?
Progeny testing is testing the value of an individual’s genotype by looking at the progeny produced by different matings
Can be used in plant or animals, but more important in animals because of their commercially important characteristics
artificial insemination in cattle
- male semen is placed directly into the vagina to uterus of the female using a catheter.
what are the three most commonly used techniques for collecting bull semen?
- artificial vagina
- digital manipulation
- electroejaculation
facts about artificial vagina
- male must be conscious
- male must not be risk to humans
- often used for cattle & horse breeding
- uses thermal and mechanical stimulation
- male mounts and penis is diverted into AV
what’s the role of a “teaser cow” and what are male steers often used instead of female cows?
Teaser animals are mounted by the bull . They should be calm and a similar size to the bull
Female teasers are not recommended because of the risk of them becoming inseminated and risk of spreading venereal disease so may steers are used instead
give 2 reasons why electroejaculation used to collect semen from wild animals e.g. lions?
- Animal must be anaesthetised before removing semen
- Does not require a mount animal
- Electroejaculation units are small, portable and battery operated and so can be used in the field
advantages of artificial insemination?
- sperm can be shipped to any country
- access to range of males
- saves stress of mating
- AI quickly available when needed
- saves cost of buying male
what are the disadvantages of AI?
- damage of stored sperm
- requires vet/skill
- cost high
- unnatural, unethical
- problems should sire have genetic defect
what are the problems with traditional selective breeding techniques in animals?
- Length of gestation period in mammals can restrict the rate of selective breeding
- Small number of offspring produced by each animal will also restrict selective breeding
How are selective breeding problems resolved?
- cloning livestock embryos
- cloning embryos and transfer to surrogate mothers
how do you split embryos? (STEPS to zygote)
- (Choose cow with desirable characteristic e.g. high milk yield
- Choose bull with desirable characteristic e.g. offspring have high milk yield)
Cow is treated with hormones to stimulate egg production – superovulation
Collect ova/eggs by flushing out from the oviduct
Collect sperm
invitro fertilisation to form a zygote
how do you split embryos? (STEPS to implantation)
zygote
mitosis
16 cell embryo grown in vitro
split embryo in vitro
Embryos implanted into surrogate mother cows
Mitosis & differentiation occurs
Produce genetically identical clones
what must be remembered about cloning?
Clones are all genetically identical to each other BUT not genetically identical to the parents.
method of cloning and embryo translation
Desirable female superovulated using follicle stimulating hormone (FSH)
Desirability of female and male, determined by progeny testing
Eggs are harvested
Eggs are fertilised in vitro (IVF)
OR female inseminated by male (AI)
Embryos are washed out of uterus
Embryo may be cloned (embryo splitting)
Embryo may be genetically tested for genetic defects or sexed
Embryos may be implanted in surrogate
Surrogate treated with hormones to prepare uterus and synchronise oestrus
Embryo may be implanted into different species (important with endangered species)
Embryo may be temporarily implanted in small ‘portmanteau’ species e.g. rabbit for transport
Embryos are frozen for future
More than one embryo can be implanted at same time
diagram of cloning using somatic cell nuclear transfer
uses of reproductive cloning?
- this is used to make a complete organism that is genetically identical to another organism
- could be used to save endangered animals
- could be used to produce elite animals
- pet cloning
- used to produce animals for research
advantages of nuclear transfer for selective breeding?
Controls genetic variability – all the variables that come from genetic differences are removed therefore results are more reliable
disadvantages of nuclear transfer
- It is expensive
- A varied response typical of a normal population may not be seen
- Clones may have unknown health issues
ethics around cloning
- animal welfare
- human impact (safety of livestock used for food)
- environmental impacts
why is IVF used?
- to treat male and female infertility
- used as a research tool in animal breeding
- used in genetic screening
what are some examples of males having difficulty conceiving?
- Sperm ducts blocked
- Sperm produced has low motility
- Low sperm count
- Impotence
- Sexual dysfunction
what are some examples of females having difficulty conceiving?
- Ovaries do not produce ova
- Oviduct blocked
- Fertilised oocyte fails to implant
- Cervical mucus produces anti- sperm antibodies
- Ovarian tissue destroyed e.g. by cancer treatment
- Premature menopause
what are the levels of treatment for IVF?
- enhance ovulation (clomid, gonadotrophin)
- place sperm loser to eggs in uterus: IUI (intrauterine injection)
- place sperm in dish with eggs
- place sperm inside eggs
What is the IVF procedure (Down regulation)
2-4 week treatment with hormones that prevent the release of natural reproductive hormones. Given by nasal spray or injection.
What is the IVF procedure (Follicular stimulation/ superovulation)
FSH injected daily for 7-14 days. Follicles in ovary develop into mature oocytes
What is the IVF procedure (monitoring and collection)?
ovaries monitored using ultrasound and oocytes collected from ripe follicles via a catheter
What is IVF procedure? (STEP 4)
Eggs and sperm are placed in a sterile nutrient solution and mixed to allow fertilisation (outer layer of oocyte may be deliberately damaged)
What is the IVF procedure? (implantation)
1 or 2 embryos are transferred to uterus as a ball of 8 -16 cells. Surplus embryos may be frozen
what is an additional process that can be used for IVF?
It is possible to remove one cell from the developing embryo and test for genetic defects prior to implantation – pre implantation genetic diagnosis (PIGD)
What are the ethics of artificial insemination?
- Conflict between need for donor anonymity and child’s right to genetic information about parent
- Allows women without a male partner to have a child
- There may be pressure on potential donors to undergo genetic testing
- Donor and recipient should ‘match
What are the issues with IVF in terms of babies and pregnancy?
- risk of multiple births
- IVF babies may be more likely to be premature and may be lighter
- What happens to ‘spare’ embryos and who owns them?
what are the risks to female (IVF)?
Risk of ovarian hyper stimulation syndrome (OHSS)
issues surrounding pre-implantation genetic diagnosis?
- Moral status of embryo
- Reduction of genetic disease in next generation
- Financial benefit to society
- Creation of saviour siblings?
- Eugenics?
risks surrounding cloning
- High failure rate
- Developmental problems
- Abnormal gene expression
what is the first stage of plant fertilisation?
after the pollen grain lands on the stigma, the tube cell produces a pollen tube through the style into the ovule
what is the third stage of plant fertilisation?
after they reach the ovule, one of the gametes (male) fuses with the female gametes leading to fertilisation
what is the second stage of plant fertilisation?
the male gametes travel along with the tube nucleus through the pollen tube
what is the fourth stage of plant fertilisation?
- fertilisation leads to the formation of zygote
- the other male gamete fuses with the polar nuclei to eventually form endosperm
what is the fifth stage of plant fertilisation?
- The zygote divides multiple times to form an embryo within the ovule.
- The endosperm provides nourishment to the embryo
- eventually the ovule develops and turns into a seed
