genetics

Question 1

genetics

Answer 1

• 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

Question 2

Mendelian Inheritance

Answer 2

• the first clear explanation of patterns of inner was by Gregor Mendel in 1865
• He studied the reproductive behaviour of pea plant

Question 3

Mono hybrid crosses

Answer 3

• 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)

Question 4

Alleles

Answer 4

• 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

Question 5

Homozygous

Answer 5

when two alleles are the same, the individual is homozygous for that allele (GG and gg)

Question 6

heterozygous

Answer 6

when these two alleles are different (hybrid), the individual is heterozygous (Gg)

Question 7

Genotype

Answer 7

the combination of alleles for a particular trait is called the genotype
- genotype: the genotype is an organism’s genetic information,

Question 8

phenotype

Answer 8

the physical appearance or what the offspring looks like is called the phenotype
- the phenotype is the set of observable physical traits

Question 9

First and second filial generation

Answer 9

• 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

Question 10

Co-dominance

Answer 10

• 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

Question 11

Incomplete Dominance

Answer 11

• 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

Question 12

Multiple Alleles

Answer 12

• 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

Question 13

chromosomes

Answer 13

• 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

Question 14

sex determination

Answer 14

• 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

Question 15

sex-linked characteristics

Answer 15

• 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

Question 16

red-green colour blindness

Answer 16

• 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

Question 17

haemophilia

Answer 17

• 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

Question 18

autosomal inheritance of single gene disorders

Answer 18

• 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

Question 19

dominant - autosomal inheritance of single-gene disorders

Answer 19

• 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

Question 20

huntington’s disease

Answer 20

• 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

Question 21

recessive - autosomal inheritance or single-gene disorders

Answer 21

• 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

Question 22

phenylketonuria (PKU)

Answer 22

• 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

Question 23

cystic fibrosis

Answer 23

• 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

Question 24

genetic counselling

Answer 24

• 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

Question 25

what is DNA profiling

Answer 25

• 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

Question 26

DNA profiling applications

Answer 26

• 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

Question 27

creating a DNA profile

Answer 27

• 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).

Question 28

electrophoresis

Answer 28

the pieces of DNA are sorted according to size using gel electrophoresis

Question 29

gel electrophoresis

Answer 29

• 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.

Question 30

DNA profiling using gel electrophoresis

Answer 30

• Each white band represents a segment of DNA.
• The smaller fragments travel through the gel faster (and therefore further) than the heavier ones.