Simple Inheritance in Animals and Plants Flashcards
What is cell division necessary for?
The growth of an organism or for the repair of damaged tissues
What are alleles?
Versions of a particular gene
Genes controlling the same characteristic
What is mitosis?
Asexual cell divison where two identical cells are formed
When do animal cells differentiate?
Early in development
Therefor cell division is mostly for repair replacement (especially mitosis)
When do plant cells differentiate?
They can differentiate throughout the life of the plant as it continues to grow
Complete the sentence:
Cells of offspring produced by asexual reproduction are produces by…
…mitosis from the parent cell.
They contain the same alleles as the parents
What are stem cells?
Undifferentiated cells with the potential to specialise into a wide variety of different cell types
What happens to the chromosomes before a cell divides via mitosis?
A copy of each chromosome is made.
One of each chromosome then goes into the new cells
Draw and label a diagram showing the stages of mitosis
- A normal body cell has 23 pairs of chromosomes (2 are shown for simplicity)
- As cell division starts, a copy of each chromosome is made
- The cell divides in two to form two daughter cells
- Each daughter cell has a nucleus containing four chromosomes identical to the ones in the original parent cell
What types of cells divide by meiosis?
Cells in reproductive organs to form gametes
What are gametes?
Sex cells.
They contain half the genetic material of ordinary body cells
Each gamete has only one gamete from each original pair.
What does this mean?
All of the gametes are different from each other and the parent cells
Why does sexual reproduction result in variation?
The gametes from each parent fuse.
So half the genetic information comes from the father, and half from the mother.
When the gametes join at fertilisation, a single body cell with new, unique, pairs of chromosomes is formed
Describe the process of meiosis
- Before division, a copy of each chromosome is made
- The cell now divides twice to form four gametes
- Each gamete has a single set of chromosomes, each with a different combination of genes
Draw and label a diagram showing meiosis
Are stem cells specialised?
No!
They can differentiate into lots of different types of cells
Where are stem cells found?
In human embyos and bone marrow
What is it hoped that one day we’ll be able to do with stem cells?
Make them differentiate into the cells we want.
These cells could then be used to treat conditions such as paralysis, e.g. by differentiating into new nerve cells
Who was Gregor Mendel?
A monk who worked out how characteristics were inherited
He was the first person to suggest the idea of seperately inherited ‘factors’
Why did it take a long time for Mendel’s ideas to be accepted?
Because scientists at the time did not know about chromosomes and genes until after he died
What are Mendel’s ‘factors’ now known as?
Genes.
Genes are found on chromosomes
Describe the structure of DNA
A very long molecule with a double helix structure
What is a DNA fingerprint?
Pattern produced by analysing the DNA which can be used to identify an individual
Does everyone have unique DNA?
Yes, except identical twins
(So… no)
What does each gene do?
Code for a particular combination of amino acids which made a specific protein
How many pairs of chromosomes do humans have?
23 pairs
What sex chromosomes do females have and what ones do males have?
Females have two X chromosomes
Males have an X and a Y
What is a sex chromosome?
A chromosome which carries the information on the sex of an individual
If an allele ‘masks’ the effect of another, what is it?
Dominant
If an allele is ‘masked’ what is it?
Recessive
What are genetic diagrams?
Biological models which can be constructed to predict and explain the inheritance of particular characteristics
What is a phenotype?
The physical appearance of a characteristic
What is a genotype?
The genetic make up of a characteristic
What does homozygous mean?
Both alleles are the same
What does heterozygous mean?
The alleles are different
What is polydactyly and what is it caused by?
Where an individual is born with extra fingers or toes
It is caused by a dominant gene
What is cystic fibrosis and what causes it?
Genetic disorder affecting the cell membranes and causes the production of thick, sticky mucus.
The mucus can effect several organs, including the lungs and pancreas
It is caused by two recessive genes
If someone has the gene for cystic fibrosis (or another recessive genetic disorder) but is not affected by it, what are they?
A carrier
How can you tell which gene is the dominant one is a Punnet square?
It has a capital letter
What is embryo screening?
Tests carried out on embyos to diagnose potential/new genetic disorders before the baby is born
How is embryo screening carried out?
- Embryonic stem cells are taken from spare embryos from IVF
- Embryos are created from adult cells
- Embryos may be taken from the umbilical cord of newborn babies
What could embryonic stem cells be used for?
To grow new tissues and organs for transplants
Why are some people concerned about the use of embryos in embryo screening?
- The research is experimental (we don’t know the outcomes)
- The embyos have the potential to be babies and are destroyed
- The embryo cannot consent
- The research is expensive
The results of embryo screening tests may give the parents choices. What might these be?
Whether or not to terminate the pregnancy
Some parents decide this is not ethical but can still prepare for the delivery of an affected baby
What happens in IVF when embyos are screened?
Only the healthy embryos are implanted into the mother
Embryos carrying faulty genes are destroyed and some people think this is unethical
