5 Simple inheritance in animals and plants Flashcards
Why do organisms need new cells?
to grow
to replace cells which are worn out and to repair damaged tissue
What is a gene?
a small packet of information that controls a characteristic or part of a characteristic of your body
it is a section of DNA
What is an allele?
different forms of the same gene
What is a chromosome?
genes grouped together
How many chromosomes are in the nucleus of a human body cell?
46
23 pairs
How does the human body gain 46 chromosomes?
One of each pair is inherited from your father and one from your mother
your sex cells - gametes only have one pair of each pair of chromosomes
What is mitosis?
the cell division in normal body cells which produces two identical cells
What happens in asexual reproduction?
cells of the offspring are produced in mitosis from the cells of their parent
contain exactly the same alleles as their parent with no genetic variation
Why is mitosis important?
must replace cells which are constantly being lost
e.g. skin - must make new cells to replace those lost from the surface
300 million body cells die each minute
What is the name given to cells which are unspecialised?
stem cells
Where can we find stem cells in humans?
human embryos have only unspecialised cells which specialise over time
can also be found in adult bone marrow but not as effective
What is the name given to cells which have now got a particular job e.g. liver, skin or muscle cells?
they have differentiated
What does it mean when a cell has differentiated?
when they divide in mitosis they can only form more of the same type of cell
restricted
Are plants cells differentiated?
no
they continue to grow for their entire life and don’t differentiate permanently
How easy is it to clone plants and animals?
plants = easy because they can become unspecialised and undergo mitosis many times to form a clone animals = difficult because cells are permanently differentiated - must use embryo
What is meiosis?
cell division takes place only in reproductive organs of animals and plants
in humans this is the ovaries and the testes
meiosis results in sex cells, called gametes, with only half the number of chromosomes (ova and sperm)
How does meiosis work?
the genetic material is copied
cell divides twice to form four gametes, each with a single set of chromosomes
What happens during fertilisation?
each gamete has a single set of chromosomes
they fuse together, sharing DNA to create a single cell with a full set of chromosomes
once complete, the unique ovum (genetically varied) begins to divide by mitosis to form a new individual etc.
What are the differences between sexual and asexual reproduction?
sexual = gametes produced by meiosis in sex organs of parents, introduces variety as each gamete is different, one set of chromosomes from each parent fuses together
asexual = produced as a result of mitosis from parent cells, contain exactly the same chromosomes and genes as the parent, no genetic variation
What is a zygote?
a single new cell formed from an egg and sperm cell fusing
Why do adults have stem cells in tissues?
in order to replace damaged cells caused by injury or disease
How can we use stem cells?
to treat previously incurable conditions…
- can be encouraged to grow any type of cell in the body
- could grow nerve cells for spinal cord injuries
- could grow whole, new organs for transplants
- to treat blindness
What are the problems with using stem cells?
- most embryonic stem cells come from aborted embryos and spare embryos in fertility treatment which raises ethical issues
- religious groups among others believe it is wrong to use them as they question whether it right to use a potential human being as a source of cells, even if it to cure others
- embryo can’t give permission which is seen by some as a violation of human rights
- concern that using embryonic cells may cause cancer if they are used to treat sick people
- making stem cells is a slow, difficult and expensive process
- hard to control stem cells and progress is slow
What is the ‘future’ of stem cell research?
- embryonic cells have been found in the umbilical cord of newborn which could help overcome some ethical concerns
- new ways have been found to grow adult stem cells found in bone marrow and other tissues, even though there is only a limited amount of cell types currently it could help avoid using embryos
- therapeutic cloning could be used to provide cloned embryonic cells to the adult donor which would mean that organs etc made would not be rejected
Who was Gregor Mendel?
- an Austrian monk born 1822 who became a monk to get an education
- he was the first person to suggest separately inherited factors, which we now call genes
- became the father of modern genetics
- Mendel was ahead of his time, his published work in 1866 was not recognised until 1900
What did Gregor Mendel experiment?
breeding experiments with pea plants
What did Gregor Mendel discover?
- he found that characteristics were inherited in clear and predictable patterns
- suggested there were separate units of inherited material
- realised that some characteristics were dominant over others and that they never mixed together
What are chromosomes made up of?
large molecules of DNA (genes are only small sections of this)
What does DNA do?
- carries instructions to make the proteins that form most of your cell structures
- proteins include enzymes that control your cell chemistry
- genes make up chromosomes in the nucleus of the cell, they control the proteins which make up different specialised cells that form tissues which then form organs, organ systems and then makes up the whole body
What is a gene?
a small section of DNA that codes for a particular combination of amino acids, which make a specific protein
a gene is made up of many bases and the order controls which amino acids are put together…
What are long strands of DNA made up from?
a combination of 4 different bases grouped into 3s which codes for an amino acid
What can a change or mutation in a single group of bases (chemical) cause?
can change or disrupt the whole protein structure and the way it works
How does DNA differ between people?
- everyone except identical twins has a unique DNA that can be used to identify them using DNA fingerprinting
- members of the same family will have strong similarities in their DNA
What do the sex chromosomes do?
determine if your are a male or female
What is the chromosome pattern for being male/female?
female = XX male = XY
What are some features controlled by?
a single gene
What is an allele?
a version of a gene (genes have different forms called alleles)
What is a dominant characteristic?
the characteristic that sill show up in the offspring even if only one of the alleles is inherited
What is a recessive characteristic?
the characteristic that will show up in the offspring only if both alleles are inherited
What does the term homozygous mean?
an individual with two identical alleles for a characteristic
e.g. DD, dd
What does the term heterozygous mean?
an individual with different alleles for a characteristic
e.g. Dd
What is a genotype?
this describes the genetic makeup of an individual regarding a particular characteristic
e.g. Dd, dd
What is a phenotype?
this describes the physical appearance of an individual regarding a particular characteristic
e.g. dimples, no dimples
What is a genetic disorder?
a disease which is inherited
What is Polydactyly?
- when babies are born with extra fingers or toes
- most common form caused by a dominant allele
- it can be inherited from one parent who has the condition
- people can remove the extra digit if they wish
What is cystic fibrosis? (symptoms, treatment, cause etc)
- a genetic disorder which affects many organs of the body, particularly the lungs and the pancreas
- over 8500 people have it in the UK
- organs become clogged up with thick, sticky mucus which stops them working properly - reproductive system is also affected so many are infertile
- treatment includes physiotherapy and antibiotics in order to try and keep the lungs clear of mucus and infections
- enzymes are used to replace the ones that the pancreas can’t produce and thin the mucus
- there is no cure
- caused by a recessive allele so must be inherited from both parents (usually born to heterozygous parents who are unaffected)
- 1 in 25 has the cystic fibrosis allele
How could genetic diseases potentially be cured?
genetic engineering - by cutting out faulty genes and replacing them with healthy ones
genetic testing - allows people to see if they are carriers (can test embryos in IVF to put the healthiest in the womb but this raises ethical issues)
What are the arguments for in the use of embryonic stem cells?
- embryonic stem cells offer one of the best chances of finding treatments for many different and often serious conditions such as spinal injury, Alzheimer’s and diabetes
- embryos used are generally spare from infertility treatment which would be destroyed anyway
- embryos are being created from adult cells for use in research and therapy - they would never become babies
- it may be possible to use embryonic stem cells from the umbilical cord of newborn babies so that no embryos need to be destroyed for research and treatments to go ahead
- embryonic stem cells could be used to grow new tissues and organs for transplants
What are the arguments against in the use of embryonic stem cells?
- embryonic stem cell treatments are very experimental and there is a risk that they may cause further problems such as the development of cancers
- all embryos have the potential to become babies - therefore it is wrong to experiment on them and destroy them
- embryos can’t give permission to be used in experiments or treatments, therefore it is unethical
- it is taking a long time to develop any therapy that works - the money and the research time would be better spent on other possible treatments such as new drugs or using adult stem cells
What are the ethics of screening?
- people can take a genetic test for faulty alleles (e.g. Huntington’s disease is caused by a dominant allele) however it can make a hard decision as to whether to marry and have a family etc
- sometimes you can screen developing embryos to check for genetic disorders providing the option of an abortion to save the child suffering with serious problems but this raises ethical issues
- can use IVF and screening to put only healthy embryos in the womb if the family has a history of inherited disorders
