genetics Flashcards
1
Q
genetics
A
- genetics is the scientific study of genes and heredity - of how certain qualities or traits are passed from parents to offspring
- from very early times farmers recognised that characteristics of plants and animals
2
Q
Mendelian Inheritance
A
- the first clear explanation of patterns of inner was by Gregor Mendel in 1865
- He studied the reproductive behaviour of pea plant
3
Q
Mono hybrid crosses
A
- a cross is the mating of two organisms
- monohybrid cross - only one pair of contrasting alleles/characteristics studied (e.g. yellow and green seed colour in less, blue and brown eye colours)
- characteristics are represented by two letter (one for the allele inherited from the mother, one for the allele inherited from the father)
- if the allele is dominant it is w shown as a capital letter (green pod colour - G)
- the recessive allele is shown as a lower case letter (yellow pod colour - g)
4
Q
Alleles
A
- for pure-breeding plants of green seed colour, GG is used
- pure-breeding plants if yellow seed colour are gg
- Hybrid with one factor of each characteristic are Gg
- these factors, G and g, are called alleles, they are different forms of a gene
- you inherit one allele from each parent
5
Q
Homozygous
A
when two alleles are the same, the individual is homozygous for that allele (GG and gg)
6
Q
heterozygous
A
when these two alleles are different (hybrid), the individual is heterozygous (Gg)
7
Q
Genotype
A
the combination of alleles for a particular trait is called the genotype
- genotype: the genotype is an organism’s genetic information,
8
Q
phenotype
A
the physical appearance or what the offspring looks like is called the phenotype
- the phenotype is the set of observable physical traits
9
Q
First and second filial generation
A
- first filial generation of F1 generation is the first set of offspring obtained from the parental generation or “P” generation
- second filial generation or F2 generation is the offspring from the F1 generation. the F2 generation is the result of a cross between two F1 individuals
10
Q
Co-dominance
A
- Co-dominance – where two or more alleles are equally dominant
- This means that if both alleles are present, they will both be observed
- In the heterozygous condition, both alleles are expressed equally with NO blending
- Presented by using two different capital letters
- Example: dominant black (BB) + dominant white (WW) = speckled black and white phenotype (BW)
- IAIB is an example of co-dominance
11
Q
Incomplete Dominance
A
- Incomplete dominance occurs when the dominant allele is incompletely dominant, meaning it does not dominant the recessive allele entirely
- Results in the dilution of the dominant allele with respect to the recessive allele, resulting in a new heterozygous phenotype.
- Both alleles of a gene are expressed often resulting in an intermediate phenotype
- blending
12
Q
Multiple Alleles
A
- Multiple alleles – There are more than two alleles for a particular characteristic
- An example of this can be seen in ABO blood groups in humans
- A person may have the blood type A, B, AB or O determined by the alleles responsible for two different protein antigens found on the membrane of red blood cells
- Consists of two dominant and one recessive allele
- Allele IA and IB are dominant over allele i
- i is recessive
13
Q
chromosomes
A
- sex chromosomes: a type of chromosome involved in sex determination. humans have two sex chromosomes, X and Y, that in combination determine the sex of an individual
- females have two X chromosomes and males have one X and one Y chromosome
- autosomal chromosomes: the 22 pairs of non-sec chromosomes are called autosomes
14
Q
sex determination
A
- all the eggs produced by a female possess a X chromosome
- half the male’s sperm contains an X chromosome and half contain a Y chromosome
- it is therefore the father’s sperm that determines the sex of the child
- if an X-bearing spermatids fertilises the egg, the zygote will be a female, if a Y-bearing sperms fertilised the egg, the zygote will be male
15
Q
sex-linked characteristics
A
- sex linked characteristics are characteristics controlled by the genes on the sex chromosomes
- when writing genotypes of sex linked characteristics, the sex chromosomes are written as capital letters and the allele, is written as superscripts for the X chromosomes
- they may be dominant or recessive
- males, who have only one copy if the X chromosomes, are more likely to be affect by a sex-linked disorder than females, who have two copies
- e.g. red-green colour blindness, haemophilia
16
Q
red-green colour blindness
A
- the ability to distinguish between the colours red and green is controlled by a gene located in the X chromosome
- those who can’t distinguish between the two colours possess the recessive allele of this gene
- a recessive allele is able to be masked by the presence of a dominant allele in females, however this is not possible in males
- this is why the frequency of having red-green colour blindness is higher in males
17
Q
haemophilia
A
- haemophilia is another sex-linked characteristic
- a disease in which the blood clots slowly or not at all
- the defective allele is recessive and is carried on the X chromosome
- males can be either normal or haemophiliacs, females can be homozygous normal, a heterozygous carrier, or haemophiliacs
18
Q
autosomal inheritance of single gene disorders
A
- single-gene disorders are disorders caused by the inheritance of a single defective gene
- autosomal inheritance relates to traits including disorders that are inherited on the autosomal chromosomes
19
Q
dominant - autosomal inheritance of single-gene disorders
A
- caused by dominant alleles in the autosomal chromosomes
- typically, traits that are controlled by dominant allele are easily passed on as only one allele is needed to that trait to be shown
- however dominant alleles that cause severe defects in people are rarely passed on as people with such diseases frequently die before they have the opportunity to reproduce
20
Q
huntington’s disease
A
- dominant autosomal
- causes neurons to gradually break down and die
- the disease attacks areas of the brain that help to control voluntary movement, as well as other areas
- symptoms typically appear after 40 years of age
- this means that the condition is likely to be passed on to offspring, and these children may not be aware that they have inherited it
21
Q
recessive - autosomal inheritance or single-gene disorders
A
- children who are homozygous recessive for an autosomal single gene disorder will be affected by the condition
- incidence is low because the chances of a carrier from one family mating with another carrier of the same recessive condition to make a homozygous recessive child is low
22
Q
phenylketonuria (PKU)
A
- recessive autosomal
- people with this disease lack the gene that controls the production of the enzyme responsible for the conversion of amino acid phenylalanine to tyrosine
- phenylalanine accumulates in the bloodstream and becomes toxic, resulting in damage to brain
23
Q
cystic fibrosis
A
- controlled by recessive allele, dominant
- 1 in 25 australians are carriers
- a defective gene that makes the body produce abnormally thick and sticky fluid called mucus
- mucus in CF patients is very thick and accumulates in the intestines and lungs
- the result is malnutrition, poor growth, frequency respiration infections, breathing difficulties, and eventual permanent lung damage
24
Q
genetic counselling
A
- by examining the incidence of a disorder in the family tree, the probability that a a particular condition will occur can sometimes be determined
- the couple can then decide whether to risk having a baby with an inherited disorder
- although genetic counselling and modern diagnostic techniques can alleviate much suffering, the responsibility for decision making must lie with the individuals concern. the decision to risk having child with a genetic disorder, or to terminate a pregnancy, is not made lightly
25
Q
what is DNA profiling
A
- identifies the unique genetic makeup of individuals and can be used to determine parentage
- every individual’s DNA is inherited from his or her parents and is unique
- definition: a technique that uses banding patterns of DNA fragments as a means of identification
- patterns occur due to size differences of fragments
- everyone’s DNA profile is unique (except identical twins)
- DNA profiling - also known as DNA fingerprinting
26
Q
DNA profiling applications
A
- establishing an individual’s identity (e.g. that of a corpse or in crime investigation)
- determining their parentage
- in anthropological research
- detecting genetic disorders and/or mutations
27
Q
creating a DNA profile
A
- a DNA profile can be created fr in a very tiny sample of DNA (e.g from the saliva or a fingerprint on a glass). A profile can even be established from very old or damaged DNA.
- from a single sample many copies can be produced using a technique called the polymerase chain reaction (
- there are many differences in the DNA of different people and it is not practical to look at all of em
- usually, ten key sections of DNA are studied. the DNA lengths are known to vary widely between individuals in each of these sections
- each section is isolated using restriction enzymes that cut the DNA strange at specific sequences
- the sections of DNA are inherited from both parents
- when the ten sections are analysed it is highly unlikely that anyone else will share the same pattern of repeats (≈ 1 in a billion chance of someone having exactly the same lengths of DNA for all of the 10 sections).
28
Q
electrophoresis
A
the pieces of DNA are sorted according to size using gel electrophoresis
29
Q
gel electrophoresis
A
- the samples to be tested are injected into small wells in a sheet of porous, jelly-like material
- an electric current is passed through the gel and the fragments are drawn towards the positive end, with small fragments travelling faster than the larger ones.
30
Q
DNA profiling using gel electrophoresis
A
- Each white band represents a segment of DNA.
- The smaller fragments travel through the gel faster (and therefore further) than the heavier ones.
