B2.7 + 8 Cell Division and Inheritance + Speciation Flashcards
Where are pairs of chromosomes found?
In the nucleus
What is a ‘gene’?
A section of DNA containing instructions to make a specific protein
How do cells code for proteins?
- Each gene codes for a particular combination and order of amino acids which make a specific protein.
- DNA also determines what protein the cell produces which determines what type of cell it is e.g haemoglobin - red blood cell
Name 2 exceptions to the rule of everyone having unique DNA
- Identical twins
- Clones
Name 2 uses of DNA fingerprinting
- Forensic science: DNA taken from a crime scene is compared with suspect’s DNA
- Paternity testing
What do chromosomes contain?
Genetic information
What are two uses of mitosis?
- Growth
- To produce replacement cells for damaged ones
How many chromosomes do diploid cells have?
46 (23 pairs)
How many chromosomes do haploid cells have?
23 (no pairs)
What are the only haploid cells in the body?
Gametes
What are the reproductive organs of a male?
The testes
What are the reproductive organs of a female?
The ovaries
What is meiosis?
A type of cell division producing gametes, cells with half the number of normal chromosomes
What is mitosis?
A type of cell division when a cell reproduces itself by splitting to form two identical clones
Why do gametes only have 1/2 the number of chromosomes?
So at fertilisation a diploid number is restored to the fertilised cell
Explain the process of mitosis.
- Chromosomes are duplicated
- DNA forms X-shaped chromosomes with each ‘arm’ being an exact duplicate of the other
- They line up at the centre of the cell and attach to spindle fibres
- These fibres pull them apart and two arms of each chromosome goes to opposite ends of the cell
- Membranes form around each of the sets of chromosomes (now the new nuclei of two cells)
- They cytoplasm divides in half (Cleavage)
- Two new genetically identical cells are formed
What type of reproduction uses mitosis?
Asexual reproduction
Name an example of an organism which reproduces asexually.
Strawberry plants forming runners
Explain the process of meiosis.
- Chromosomes duplicate
- In the first division, the chromosomes line up at the centre of the cell
- Pairs are pulled apart to the opposite ends of the cell, so each new cell only has one copy of each chromosome
- Some of the first cell’s and some of the second cell’s chromosomes go into each new cell
- In the second division, the chromosomes line up again in the centre of the cell, the arms are then pulled apart. (like mitosis)
- Four new gametes are formed with 1/2 the number of normal chromosomes
What happens after fertilisation?
The cell grows by repeatedly dividing with mitosis
Define differentiation
Becoming specialised for a particular function and being unable to change into other types of cell.
What is differentiation caused by?
Genes switching on and off
What is the difference between animal cells and plant cells in differentiation?
Animal cells only differentiate at an early stage once and then lose the ability whereas plant cells retain it throughout their life.
How is plant cell differentiation used?
Huge numbers of identical plant clones are grown from one tiny piece of tissue.
What is a stem cell?
Undifferentiated cells which can develop into any different type.
What are embryonic stem cells?
Stem cells extracted from very early human embryos that can differentiate into any type of cell.
How do researchers control embryonic stem cell differentiation?
By changing the environment they’re growing in.
What conditions/diseases could embryonic stem cells cure?
- Heart disease (beating heart muscle)
- Diabetes (insulin producing cells)
- Paralysis (new nerve cells)
What are adult stem cells?
Stem cells found in the bone marrow that can only differentiate into red and white blood cells
Name a condition adult stem cells can treat
- Sickle cell anaemia (new blood cells)
Why are people against stem cell research?
- Human embryos are potential life
- Embryos have no say
- Scientists should use other sources of stem cells rather than embryos
What is an ‘allele’?
Different versions of the same gene which determine different characteristics.
What are the offspring of asexual reproduction like?
They have the same alleles as their parents
What are the offspring of sexual reproduction like?
They have variation, a combination of alleles from both their parents.
What pair of chromosomes determines the male sex?
XY
What pair of chromosomes determines the female sex?
XX
Define ‘dominant allele’
An allele that produces the same phenotype whether its paired allele is identical or different.
Define ‘recessive allele’
An allele that only produces the same phenotype if its paired allele is identical.
Define ‘homozygous’
An individual which two identical alleles for a characteristic
Define ‘heterozygous’
An individual which two different alleles for a characteristic
Define ‘genotype’
The genetic make up of an individual regarding a particular characteristic
Define ‘phenotype’
The physical appearance of an individual regarding a particular characteristic
What is the shape of a DNA molecule?
A double helix
Who was Mendel?
A monk who discovered the laws of inheritance by breeding pea plants.
Why was Mendel not believed at the time about his work?
- DNA/genes hadn’t been discovered
- He was not a reputable scientist
What is poldyactyly?
A genetic disorder caused by a dominant allele where a baby is born with extra toes or fingers.
What is cystic fibrosis?
A genetic disorder caused by a recessive allele where the body produces excess mucus in the air passages and pancreas.
How are embryos screened for genetic disorders?
- During IVF, before implanting an embryo, a cell is removed from each one.
- Their genes are analysed
- Embryos with ‘healthy’ alleles are implanted and those without are destroyed.
What are the arguments for embryonic screening?
- It will stop people suffering
- Treating disorders costs taxpayers money
- During IVF most of the embryos are destroyed anyway
- There are laws in place to stop it going too far (e.g not allowing sex selection)
What are the arguments against embryonic screening?
- Expensive
- Can lead to designer babies
- Implies people with genetic disorders are ‘undesirable’
- Rejected embryos are destroyed - they had potential for human life.
What are fossils?
The remains of organisms from many years ago found in rocks.
Name 3 ways fossils can be formed.
- Gradual replacement by minerals
- From casts and impressions
- Preservation.
Describe how gradual replacement by minerals produces fossils.
- Teeth, shells and bones don’t decay easily
- They are eventually replaced by minerals forming a rock like substance shaped like the original part
- The surrounding sediments also turn to rock but the fossil stays distinct
Describe how casts and impressions produce fossils.
- An organism is buried in a soft material (e.g clay)
- The clay later hardens around it and the organism decays leaving a cast around itself.
Give examples of fossils that come from impressions (3)
- An animal’s burrow
- Plant’s roots
- Footprints
Describe where and how preservation produces fossils.
- In amber and tar pits there’s no oxygen/moisture so decomposers don’t survive.
- In glaciers it’s too cold for decomposers to work
- In peat bogs it is too acidic
What are fossils useful for?
Finding out how living things evolved
Why is the fossil record incomplete?
- Some are yet to be discovered
- Fossilisation is rare
- Many fossils in rocks have been destroyed due to geological activity
- Many early organisms were soft bodied and soft tissue decays
What are 6 causes of extinction?
- The environment changes too quickly
- A new predator kills them all
- A new disease kills them all
- They can’t compete with another species for food
- A catastrophic event kills them all
- A new species develops
Define ‘speciation’
The development of a new species, when populations of the same species become so different they can no longer breed fertile offspring
Define ‘species’
A group of similar organisms that can reproduce to give fertile offspring
Describe the process of speciation
- Any population contains genetic variety - they have a wide range of alleles that control their characteristics
- if one population becomes isolated from the other, the conditions they are living in are likely to be different
- Natural selection will therefore occur differently in each group and the alleles selected that control the characteristics which help an organism survive will be different
- Eventually the two populations will have changed so much over time that they can’t interbreed successfully
