Genetics Flashcards
1
Q
What is genetics?
A
- a branch of biology that studies heredity and variation in organisms
2
Q
What does genetics try to explain?
A
- both the similarities and differences between parents and their offspring
3
Q
Who was the ‘father of genetics’?
A
- Gregor Mendel
- an Austrian monl
4
Q
What realisation did Mendel have?
A
- that ‘something’ is passed on from parent to offspring
- that sexual reproduction combines these ‘somethings’ from each parent
- to produce offspring which are unique, yet the same
5
Q
What are the factors passed from parent to offspring?
A
- genes
6
Q
What is each chromatid made up of?
A
- 1 helical DNA molecule
7
Q
What is each DNA molecule made up of?
A
- a series of genes
8
Q
What is a gene?
A
- a section of DNA (series of nucleotides/bases) that controls a hereditary characteristic (trait)
- ie it is the basic unit of heredity in living organisms
9
Q
What do nearly all somatic cells have?
A
- an exact copy of all the genes in that organism
10
Q
Why does each cell contain 2 of each kind of gene (before replication)?
A
- because there are 2 of each kind of chromosome (paternal and maternal)
11
Q
What is a gene pool?
A
- the set of all genes, or genetic information, in a population of sexually reproducing organisms
12
Q
What does a large gene pool indicate?
A
- high genetic diversity
- increased chances of survival
13
Q
What does a small gene pool indicate?
A
- low genetic diversity
- increased possibility of extinction
14
Q
How active are genes?
A
- only the genes that are needed are activated and the other suppressed
- different genes are activated in different cells, creating the specific proteins that give a particular cell type its character (e.g. bone cells, brain cells, skin cells etc.)
15
Q
What are ‘housekeeping genes’?
A
- genes that are active in many types of cells, making proteins needed for basic functions
16
Q
What are hox genes?
A
- master control genes that determine the way in which the body develops from a single zygote
17
Q
What are alleles responsible for?
A
- genes responsible for controlling different versions of a trait/characteristic found in the same locus on homologous chromosomes
18
Q
What is the control of genes called?
A
- epigenetics
19
Q
What are alleles?
A
- one of two or more forms of a gene
20
Q
How are alleles passed from parent to offspring?
A
- by way of chromosomes in the gametes that are made by the process of meiosis in the sex organs
21
Q
What happens to the gametes during fertilisation?
A
- a male gamete fuses with a female gamete to form a diploid zygote
- this divides by mitosis to form an entire new organism made up of cells
- each with the same set of chromosomes and alleles as in the zygote
22
Q
What is a genotype?
A
- a genotype is made up of all the genes an organism carries on its chromosomes which it has inherited from its parents
23
Q
What is a phenotype?
A
- the physical appearance of an organism
- partly programmed by genes, its genotype, and also external factors such as exercise, diet and environment
24
Q
When is an organism homozygous for a particular trait?
A
- if the pair of alleles at a locus are the same
25
When is an organism heterozygous for a particular trait?
- if the pair of alleles at a locus are different
26
What are the kind of alleles in a heterozygous pairing?
- dominant
- recessive
27
What is a dominant allele?
- the trait that is expressed in the offspring
28
What is a recessive allele?
- the trait that is suppressed in the presence of the dominant allele and not expressed in the offspring
29
What is a monohybrid cross?
- a cross between parents with different alleles for a single gene
30
How are generations shown in genetic diagrams?
- P1 - parent generation
- F1 - first filial generation of offspring
- F2 - second filial generation of offspring
31
What is a punnet square?
- an easy way to represent a cross between 2 organisms for any number of characteristics for which the parental genotypes are known
32
What does a punnet square do?
- predicts the probability of the offspring's genotype and phenotype
- is the basic tool used for Mendelian genetics
33
What is complete dominance?
- a characteristic that is fully expressed in the phenotype of a heterozygous organism
34
What is stated in Mendel's law of segregation?
- during meiosis, allele pairs separate (segregate) so that the gametes have a single allele for each characteristic
35
What is stated in Mendel's law of dominance?
- in a cross of parents that are pure for contrasting traits, only the dominant trait will appear in the phenotype
- recessive alleles will always be masked by dominant alleles
36
What is stated in Mendel's law of independent assortment?
- the alleles of different genes segregate randomly and independently of one another during gamete formation
37
Which pair of chromosomes are the sex chromosomes/gonosomes?
- pair 23
38
What sex chromosome combination codes for a female?
- XX
39
What sex chromosome combination codes for a boy?
- XY
40
What is the sex of an organism determined by?
- the presence or absence of the Y chromosome
41
What is the inheritance of sex a special form of?
- inheritance of sex is a special form of monohybrid inheritance
42
How is the Y chromosome structured in relation to alleles?
- the Y chromosome is very short and has very few alleles on it other than those responsible for 'maleness'
43
How is the X chromosome structured in relation to alleles?
- the X chromosome is much longer and can carry many alleles along its length in addition to those for 'femaleness'
44
What are x-linked genes/sex-linked?
- the alleles that are carried on the non-homologous part of an X chromosome
45
What are some examples of sex-linked diseases?
- cleft palate
- diabetes insipidus
- red-green colour blindness
- haemophilia
- muscular dystrophy
46
Why do certain genetic diseases seem to occur more often in males than in females?
- because the male has only 1 X chromosome
- so if a gene mutates or if a gene for a disease is present on this X chromosome, the male will get the genetic disease
- if the gene is recessive, it will only be expressed in the female if both X chromosomes have the allele
47
What are examples of diseases caused by a recessive sex-linked allele on the X-chromosome?
- red-green colour-blindness
- haemophilia
48
What is the main characteristic of polygenic inheritance?
- there is more than one pair of alleles responsible for a single trait
49
How are the complex traits found in polygenic inheritance determined?
- they are determined by the interaction of many different alleles
- each having small individual effects on the offspring
- resulting in a range of phenotypes
50
What is continuous variation?
- graduations of a characteristic in a phenotype
- e.g. height in humans
51
How does continuous variation work?
- the more pairs of alleles that control a characteristic, the greater the number of possible combinations and the greater the variety of phenotypes
- each phenotype differs slightly from the next, forming a graduated series
52
What are some examples of continuous variation in polygenic inheritance?
- height
- skin colour
- metabolic rate
- longevity
53
What is a mutation?
- a sudden change in the genetic makeup (DNA) of an organism
54
How does a gene mutation occur?
- from a change in the sequence of nucleotides in a DNA molecule
- causing a change in the information the gene gives to the cell
- i.e. the codons will be altered which will result in a faulty protein or no protein at all being made
55
What are mutagens?
- factors that increase the rate of mutations
56
What are some examples of environmental mutagens?
- ionising radiation (ultraviolet light and X-rays)
- mutagenic chemicals
- viruses
- micro-organisms
57
What are the different types of cell mutations?
- somatic mutations
- gametic mutations
58
What are the characteristics of somatic mutations?
- occur in body cells
- not transmitted to the next generation
- can cause cells to become malignant, resulting in cancer
59
What are the characteristics of gametic mutations?
- occur in the reproductive organs (ovaries, testes, anthers, embryo sacs)
- produce changes to the genes in the gametes
- these germ-line mutations may lead to variation in the offspring
- eventually by accumulating these changes, a new species may evolve, a process called speciation
- may lead to hereditary diseases
60
What are the 3 kinds of mutations?
- neutral mutations
- beneficial mutations
- harmful mutations
61
What are the effects of neutral mutations?
- they do not affect the life of the organism
62
When do beneficial mutations occur most often and why?
- amongst viruses and bacteria
- due to their rapid reproduction rate
- e.g. new multi-resistant bacteria that have mutated to become resistant to antibiotics
63
How does natural selection occur as a result of beneficial mutations?
- when a mutation leads to a change in the phenotype
- resulting in organisms adapting better to new or unfavourable conditions
- allowing them to survive and breed more successfully than the rest of the population
64
What happens as a result of natural selection and beneficial mutations?
- in time the whole population will have the new genotype and a new species will have been formed
- i.e. speciation has occurred
65
How are harmful mutations usually inherited?
- as autosomal recessive traits
66
What does autosomal mean?
- relates to chromosomes that are not sex chromosomes
- i.e. numbers 1 to 22
67
How do harmful mutations occur?
- the heterozygous parents each have one normal copy of the gene and one mutated, non-functional copy
- the homozygous recessive individuals exhibit the disorder because both gene copies are non-functional and the correct gene product, a protein, is missing
68
What is a genome?
- the complete set of genetic instructions necessary to create an organism
69
What is the Human Genome Project (HGP)?
- an international scientific research project set up in 1990
70
What are the primary goals of the HGP?
- to determine the sequence of chemical base pairs which make up human DNA (DNA sequencing)
- to identify and map all the genes of the human genome from both a physical and functional point of view
71
What is the importance of learning more about the functions of genes and proteins?
- it has a major impact on the fields of medicine, biotechnology and life sciences
- e.g. genes have been discovered that are linked to Alzheimer's, bad cholesterol and heart disease and breast cancer association
72
What are genetic counsellors?
- health professionals with specialised graduate degrees and experiences in the areas of medical genetics and counselling
73
What do genetic counsellors do?
- provide information and support to families who have members with birth defects or genetic disorders
74
What sort of issues could be discussed by genetic counsellors?
- whether a couple should have children if both are carriers of a faulty gene
- if artificial insemination is a practical alternative to the problem
- if in vitro fertilisation is a possible option
- whether cousins should contemplate having children
75
What does a family pedigree show?
- the pattern of inheritance of a particular characteristic
76
What does a family tree show?
- the genotypes and phenotypes of several generations of individuals in a family
77
How are family trees useful?
- can be used to predict whether a couple is likely to pass on a genetic disorder
