B12 Flashcards
What is DNA?
Chemical that all of the genetic material in a cell is made up from. It is a polymer that is made up of two strands coiled together in the shape of a double helix.
What does DNA contain?
Coded information , the instructions to put an organism together and make it work
Where is DNA found?
In the nucleus of animals and plants , in really long structures called chromosomes
How do chromosomes usually come?
In pairs
What is a gene?
Small section of DNA found on a chromosome. Each gene codes for a particular sequence of amino acide which are put together to make specific proteins.
How many amino acids are there?
20 but make up thousands of different proteins
What is the genome?
Entire genetic material of an organism.
Why the genome is important?
Understanding it is important for science and medicine.
- allows scientists to identify genes links to different types of diseases, which could help find treatments
- also to see human migration patterns
What is sexual reproduction?
Where genetic information from two organisms combine to produce offspring which are genetically different to either parent
What happens in sexual reproduction.
Gametes are produced by mother and father by meiosis (egg and sperm cells). Each gamete contains 23 chromosomes in a normal cell. Egg and sperm fuse together to form a cell with a full number of chromosome
What does sexual reproduction involve?
The fusion of male and female gametes. There are two parente , the offspring contain a mixture of their parents genes
What is fertilisation?
When the sperm meets an egg producing offspring
Why does offspring inherit features?
Receives a mixture of chromosomes from its mum and its dad. The mixture produces variation
Examples of gametes?
Egg
Sperm
Pollen
Egg cells in plants
What is asexual reproduction?
Involves only one parent and no fusion of gametes. There is no mixing of genetic material. This leads to genetically identical offspring. Mitosis is involved
What is produced by asexual reproduction?
Clone
Examples of asexual reproduction?
Bacteria, some plants, some animals
How are gametes produced
Meiosis
How do you make gametes with only half the original number of chromosomes?
Cells divide by meiosis which involves two cell divisions
What must happen before meiosis takes place?
It divides its genetic information, forming two armed chromosomes , one arm of each chromosome is an exact copy of the other arm . After replication , the chromosomes arrange themselves into pairs
What happens in the first division in meiosis?
Chromosome pairs line up in the centre of the cell. They are then pulled apart so each new cell only has one copy of each chromosome. Some of the fathers chromosomes and some of the mothers go into each new cell.
What happens in the second division in meiosis?
Chromosomes line up again in the centre of the cell. The arms of the chromosomes are pulled apart .
Product of the second cell division?
Get four gametes each with only a single set of chromosomes in it . Each gamete is genetically different form the others because the chromosomes all get shuffled up during meiosis and each gamete gets half of the, at random
Where are gametes formed?
In the reproductive organs
What happens when two gametes fuse?
Result in new cell that divides by mitosis. Mitosis repeats many times to produce lots of new cells in an embryo . As the embryo develops they start to differentiate into different specialised cells
How many pairs of chromosomes in every human cell?
23
How many pairs control sex of the animal?
1/23
What chromosomes do males have?
XY
What does the Y chromosome cause?
Male characteristics
What chromosomes do females have?
XX
What happens when making sperm?
X and Y chromosomes are drawn apart in the first division of meiosis. 50% chance a sperm cells gets and x chromosome and 50% chance it gets a Y
How do you find the probability of getting a boy or girl?
Draw a genetic cross diagram
What are genetic cross diagram?
Models that are used to show all possible genetic outcomes when you cross together different genes or chromosomes
How to make a genetic cross diagram?
Put the possible gametes from one parent down one side and the same on the other side for the other parent. Then fill in the squares from the top and the side , pairs in the middle show the possible combinations
What do the genes inherited control?
What characteristics you develop. Different genes control different characteristics , some are controlled by a single gene
How are most characteristics controlled ?
Several genes interacting
What are alleles?
A different form of gene e.g if the gene is eye colour , the alleles could be blue eye gene , brown eye gene
What is a chromosomes?
Long coild structure composed of DNA
Stages of Meiosis simplified?
1) DNA replicates
2) cell divides twice to form 4 genetically non identical gametes
3) each gamete contains a single set of chromosomes(23 chromosomes)
What is the dominant allele?
An allele that is expressed ( even if there is only one dominant allele
What is the recessive allele?
An allele that is masked by a dominant allele. Recessive alleles are only expressed if they occur in pairs e.g bb, tt
What doe homozygous mean?
Genotype where an individual has two identical alleles for a specific gene e.g BB,tt,pp
What does heterozygous mean?
Genotype where an indiviudal allele has 2 different alleles for a specific gene e.g Bb ,Tt,Pp
What is the phenotype?
Physical expression of ones genotype due to its interaction with the environment , e.g tall, small, blonde, brown eyes
What is the genotype?
Genetic constitution of an organism, AA, Tt, rr
What is a gamete?
Sex cell that contains half the number of chromosomes than a normal body cell
How do you answer this question:
A black haired heterozygous man and a blonde haired homozygous female are having a child. What is the % probability of the child having black hair?
B=black hair
b=blonde hair
Parent phenotype: black hair x blonde hair
Parents genotype : Bb x bb
Genetic cross:
Gametes :B(sperm) b(sperm) b(egg) b(egg)
Offspring phenotype: black hair, black hair , blonde hair, blonde hair
Probability: 50:50
How do alleles operate?
Alleles or genotype, operate at a molecular level to develop characteristics that can be expressed as a phenotype
What is cystic fibrosis?
Genetic disorder of the cell membrane. It results in the body producing a lot of thick sticky mucus in the air passages and in the pancreas
What is the allele of cystic fibrosis?
Allele that causes it is a recessive allele ‘f’ carried by about 1 in 25 people. because it is recessive , people with only one copy of the allele wont have the disorder-they’re known as carriers
What is a carrier?
Someone that carries the recessive alle of a disease , they do not have that disease.
How would someone genetically get cystic fibrosis?
Both parents must be either carriers or have the disorder themselves.
What is polydactyly?
A genetic disorder where a babys born with an extra finger or toe. Doesn’t usually cause any other problems.
How is polydactyly caused genetically?
A dominant allele ‘D’ and so can be inherited if just one parent carries the defective allele. Parent with the defective allele will have the condition too as the allele is dominant. There is a 50% chance of getting it if a parent is a carrier.
What happens during IVF?
Embryos are fertilised in a laboratory and then implanted into the mothers womb.
What can you do before you implant the embryo into the mothers womb?
Remvoe a cell and analyse its genes, you can detect the genetic disorders.
Way of getting DNA to check for disorders?
Take it from an embryo in the womb
Arguments against embryonic screening?
- prejudice against people with genetic problems.
- everyone might want to start screening embryos , changing characteristics.
- screening is expensive
- ‘bad’ alleles will be destroyed and could lead to a a termination of the pregnancy
Arguments for embryonic screening?
- help stop people suffering
- costs taxpayers a lot o money treating disorders
- laws to stop it going too far
What is variation?
Differences between species and animals in the species
How can variation be genetic?
Caused by differences in the genotype. Genotype is all of the genes and alleles that an organism has. Genotype effects the phenotype- characteristics it displays. An organisms genes are inherited from the parents.
How can variation be caused by the environment?
Interactions in daily life can change the phenotype. Eating too much changes your phenotype
What is most variation determined by in the phenotype?
Mixture of genetic and environmental factors. For examples , the maximum height an animal or plant can grow is determined by its genes , but whether it grows to that height depends on the environment.
What are mutations?
Occasionally a gene may mutate. Mutations are rare , random change in an organisms DNA that can be inherited . Mutations occur continuously. It means a gene is altered , which produces a genetic variant
What is a genetic variant?
Different form of gene
What effect do most genetic variants have?
Little to no effect on the proteins of the gene code for. Most mutations have no effect on the phenotype
What happens to the gene sometimes when a mutation occurs?
Sequence of amino acids that make up proteins, gene mutations sometimes lead to changes in the protein that it codes for.
