The Genome, Chromosomes, DNA And Genetics Flashcards
what is a chromosome?
A long strand of DNA located in the nucleus
What is a gene? (2)
- A short strand of DNA (part of a chromosome)
- that codes for a particular characteristic
What is an allele?
- An alternative form of gene
- for a particular characteristic
Define Gene Locus
The position of a gene on a chromosome
What is independent assortment? (3)
- A process that takes place during meiosis
- in which chromosomes are reassorted
- in the formation of gametes
What is meiosis? (3)
- A type of cell division
- that produces cells (gametes)
- that have half the normal chromosome number (haploid cells)
What is mitosis? (3)
- A type of cell division
- that produces cells genetically identical
- to the parent cell and each other
What is the genotype of an allele?
- The genetic arrangement of alleles (genetic make up)
- for 1 or more traits
What is meant by phenotype? (2)
- The actual appearance of alleles (genetic make up)
- for 1 or more traits
What is meant by the term homozygous?
if the individual has two identical alleles for a characteristic
e.g. AA or aa
What is meant by the term heterozygous?
If the individual has two different alleles for a characteristic
E.g. Aa
What is meant by the term recessive?
The allele that is only expressed in the homozygous form
E.g. aa
What is meant by the term dominant?
The allele that is expressed in both the homozygous and heterozygous forms
E.g. AA or Aa
What is heredity? (2)
- The transfer of genetic information (alleles)
- from one generation to the next
What are homologous chromosomes? (3)
- A pair of chromosomes
- that are the same length
- and have genes for the same characteristics
(The alleles present may be different)
What is monohybrid inheritance?
When only one trait (gene) is considered in a genetics cross
What is a back/test cross? (2)
- a test carried out to confirm the genotype of an individual
- with a pure bred homozygous recessive
(I.e. to determine if the individual is heterozygous or homozygous dominant)
What are the stages of meiosis? (2)
- where one cell divides into two
- the two cells divide to form a total of four cells
What is a genetic disorder? (2)
- A disease caused by errors in a DNA sequence,
- disorders are heritable so can potentially be passed on to offspring
What is Cystic Fibrosis? (2)
- A genetic disorder of the cell membranes that leads to excess mucus that damages organ systems,
- caused by a recessive allele
How is cystic fibrosis inherited?
only if two recessive alleles are present
What is a carrier? (2)
- An individual who carries a recessive allele for a disorder
- but does not express the disorder’s phenotype
What is haemophilia? (2)
- An inherited condition characterised by an inability to clot blood
- haemophilia is a sex-linked condition
How is haemophilia inherited? (2)
- it is a sex-linked disorder, meaning it is found on the X-chromosome
- It takes two of the allele for a woman to get the disorder, but only one is required for a male
What are sex-linked disorders? (2)
- A genetic condition caused by genes on the 23rd chromosomes or the X or Y chromosome
- they only require one copy of an allele for male inheritance, but two for females
What is Huntington’s disease? (2)
- A genetic disorder that causes progressive deterioration of brain cells,
- does not appear until older age
How is Huntington’s disease inherited? (2)
It is expressed by a dominant allele, it will always be expressed unless an individual is homozygous recessive
- you cannot be a carrier for dominant disorders
What is Down syndrome?
A condition of intellectual disability and associated physical disorders
How is Down syndrome inherited? (2)
- Caused by a genetic trait known as trisomy, where an additional copy of the 21st chromosome is present,
- it results from an extra chromosome to make a total of 47 rather than 46
What are the X and Y chromosomes?
- the 23rd pair of chromosomes in a human,
- the combination of these determines the sex of an offspring
What gender is given by XX
What is the probability of them having a XX child?
- female
- 50%
What gender is given by XY
What is the probability of them having a XY child?
- male
- 50%
How many chromosomes are in human cells? How are they arranged?
46 —> in 23 pairs
How many chromosomes are in human gametes?
23
(Half the normal number)
How is insulin produced? (8)
- use restriction enzyme to remove human insulin gene
- remove plasmid from bacterium
- cut plasmid open using restriction enzyme
- implant insulin gene into plasmid
- put plasmid into bacterium
- place bacteria in fermenter with optimum pH, temp, nutrients etc.
- bacteria reproduce
- downstreaming: extract, purify and pack insulin
Describe how the insulin gene can be incorporated into the plasmid (3)
- restriction enzyme cuts insulin gene from human DNA
- same restriction enzyme cuts plasmid open
- insulin gene joins plasmid due to complementary sticky ends
What is the structure of DNA?
Double Helix
What is meant by the genome of an organism?
All the DNA in an organism
what are the three components of DNA - what are they represented with in diagrams?
- phosphates - circles
- sugars - pentagons
- bases - blocks with names
What are the 4 bases? Which link together?
- adenine
- thymine
- cytosine
- guanine
AT
CG
What connects bases in DNA?
Hydrogen bonds
What term describes a phosphate, sugar and base
A nucleotide
What is a base triplet? (2)
- The sequence of three bases on a single strand of DNA
- that codes for an amino acid
What are the three uses of Mitosis?
- growth
- repair of damaged tissue
- replacing worn out cells
What is genetic engineering? (2)
- A process that modifies the genome of an organism
- to introduce desirable characteristics
Where are restriction enzymes used? How do they cut? (2)
- In extraction of the human insulin gene and cutting open a bacterial plasmid
- they leave sticky ends for the other gene to bond
What is Amniocentesis? (2)
- The extraction of foetal cells from amniotic fluid (by a needle) for examination,
- to test for genetic abnormalities
name two sex-linked disorders
- colour blindness
- haemophilia
What is the name of cells with half the number of chromosomes?
Haploid cells
What is the name of cells with a normal number of chromosomes?
Diploid cells
How does the DNA of individuals differ?
Each person has different base sequences
What are karyotypes?
An individual’s complete set of chromosomes
