Chapter 23 (Patterns of Inheritance) Flashcards
1
Q
Definition of a gene
A
Length of DNA
2
Q
Definition of locus
A
Position of a gene on a chromosome
3
Q
Definition of allele
A
A gene variant
4
Q
Definition of genotype
A
The combination of alleles present in a cell/organism
5
Q
Definition of phenotype
A
The physical observable characteristics that are expressed in an organism.
6
Q
Definition of haploid
A
Half the number of chromosomes
7
Q
Definition of diploid
A
The total number of chromosomes present
8
Q
Definition of heterozygous
A
A genotype consisting of two different alleles
9
Q
Definition of homozygous
A
A genotype consisting of two identical alleles.
10
Q
Definition of carrier
A
The genotype of an individual with two different alleles who doesn’t have the disease but can pass it on.
11
Q
Definition of dominant allele
A
An allele that is expressed in the phenotype
12
Q
Definition of recessive allele
A
An allele only expressed when the dominant allele is absent.
13
Q
Definition of multiple alleles
A
When there are 3 or more alleles present for one specific gene
14
Q
Definition of co-dominant allele
A
Both alleles are equally dominant and have an impact on the phenotype.
15
Q
Definition of pure breeding
A
the genotype is homozygous for that characteristic
16
Q
Definition of homogametic
A
Both sex chromosomes are identical
17
Q
Definition of heterogametic
A
Both sex chromosomes are different.
18
Q
Types of gene mutations
A
Insertion
Deletion
Substitution
‘Translocation
Non-disjunction
Inversion’
19
Q
What is substitution
A
One base is swapped for another base (point mutation)
20
Q
What is deletion
A
A nucleotide or nucleotides are removed. Causes frameshift in codons in mRNA. - leads to alteration of aa.
21
Q
What is insertion
A
An extra nucleotide or nucleotides are placed into the DNA sequence. Causes frameshift - leads to alteration of aa, so ppc.
22
Q
Definition of gene mutations
A
A chance to the base (nucleotide sequence)
23
Q
Why are insertion and deletions more likely than substitution mutations to result in a major change?
A
- The “sense” has been altered in both cases
- Every triplet after the first one has changed, producing a frameshift
- This is likely to have greater effects.
24
Q
What does PKU stand for?
A
Phenylketonuria
25
Ethical concerns regarding genetic testing
- May lead to abortion
- Parents face decision as to whether child should be born
- Risk of damage to embryo or mother
- Risk of getting false positive / negative result.
26
Symptoms of cystic fibrosis
Infertility in men because vas deferens may fail to form.
- Abnormally thick mucus in lungs and pancreas.
- prone to bacterial infections
27
How is Huntington's Disease caused.
Caused by insertion mutation on chromosome 4.
Autosomal Dominant Allele
In healthy person, CAG triplets repeated 10-26 times.
In CAG triplet repeated 40+
(Gene stutter)
28
Why is Huntington's disease dangerous
Caused by accumulation of protein fragments in neurones in brain - leads to neurone death, so reduces ability to send nerve impulses.
29
How is cystic fibrosis caused
Genetic disorder caused by a recessive allele found on chromosome 7. that codes for a transporter protein called CFTR.
30
Normal situation without cystic fibrosis.
Transporter proteins transport cl- ions out of cell, causing high conc of cl- ions built up outside cell.
This reduces water potential lower than that of cells' cytoplasm.
This draws water out of the cells by osmosis.
Water dilutes mucus, so its thin enough to be moved by ciliated epithelium. (uses respiration to produce ATP to enable wafting movement of cilia)
31
What do CFTR proteins do?
They sit in the cell surface membrane of cells in the alveoli.
They allow chloride ions to pass out of cells.
Faulty version doesn't produce a fully functioning protein, so chloride ion transport if disrupted.
32
What do CFTR proteins do for a Cystic fibrosis sufferer?
Transporter proteins don't pump Cl- ions out of cell, so no water is drawn out of cells.
mucus remains thick and viscous.
Ciliated epithelium is unable to clear mucus, nor can coughing.
Mucus accumulates (as goblet cells still produce it)
bacteria gets trapped and remains in uncleared mucus.
Bacterial infections are likely.
33
Possible treatments of cystic fibrosis
1. Daily physiotherapy
2. Administer pancreatic enzymes
3. Use of antibiotics
4. Lung transplant.
5. Inhaled anti-asthma therapy
6. (Males need fertility treatment)
34
What is Phenylketonuria caused by?
RECESSIVE
Caused by abnormal base sequence of DNA that codes for enzyme - phenylalanine hydroxylase
Affects PAH gene on chromosome 12.
Sufferers lack gene that codes for that enzyme, which breaks down PKU.
Phenylalanine accumulates in blood and tissue fluid causing severe brain damage in young children.
35
Symptoms of PKU
Mental retardation, epilepsy, behavioural issues, learning disabilities.
36
PKU testing and mutations info
All babies are tested for PKU
Different mutations can result in different severity levels of PKU
Substitution mutation - only change single aa in enzyme, so results in reduced enzyme function
Deletion mutation - Stops any enzyme activity, so prevents breakdown of Phenylalanine.
37
Treatment for PKU
Avoid foods containing high amounts of phenylalanine for whole life.
38
Symptoms of Huntington's disease
```
degenerative (progressive disorder)
Difficulty walking
Trouble swallowing
Confusion
Memory loss
Speech changes
```
39
When do symptoms start to show if you have Huntington's disease?
After age 30.
If more repeats, earlier onset because longer protein, which codes for specific function, protein will increase in length faster, so mass increases.
40
Huntington's Disease zygotes info
Zygotes who are homozygous dominant spontaneously aborted at early stage.
41
Ethical issues of testing existing children for Huntington's?
- Children too young to make decisions about their testing
- They haven't consented.
- Testing wil give them knowledge about their kids and if negative, could lead a normal life.
Psychological effects.
42
Definition of Codominance
Alleles at a gene locus that are both expressed so both contribute to the phenotype.
43
Blood groups info?
```
Blood groups are determined by cell surface antigens.
Alleles - IA, IB, IO (SUPERSCRIPT)
IA = allele for antigen A
IB = allele for Antigen B
IO= allele for no antigen
```
IA and IB are codominant
IA and IB are dominant to IO.
44
What are HLA antigens?
Human leucocyte antigens, that act as a major histocompatibility complex.
A poor match between HLA antigens of a transplanted organ and its recipient leads to rejection.
All cells have antigens on their csm.
45
HLA and genes?
3 main Class 1 MHC genes
HLA-A, HLA-B, HLA-C
3 minor Class 1 MHC genes HLA-E, HLA-F, HLA-G
46
What do the MHC genes do?
They code for proteins which display peptides to the immune system, which have been made within the cell. Immune system responds to cells with different HLA antigens like it would a pathogen. Foreign peptides are destroyed.
47
HLA antigens info?
HLA antigens coded by 6 gene loci on chromosome 6. Positioned very close together so tend to be inherited as a set - called HAPLOTYPE.
There are variants of the HLA-A,B,C.
Each HLA gene exhibits codominance.
Example of Gene linkage
48
What is gene linkage?
Inheritance of alleles on gene loci close together.
49
What is autosomal linkage?
Two or more genes that are located on the same chromosome that are inherited together.
( exception - if chiasma form during crossing over)
50
What is sex linkage?
A characteristic is sex linked if the gene that codes for it is carried on the sex chromosome.
(most are carried on X chromosome as its larger than Y)
51
Definition of homogametic
XX chromosomes (females)
52
Definition of heterogametic
XY chromosomes (males)
53
What is Haemophilia A?
- Genetic disorder
- Determined by recessive allele carried on X chromosome.
Results in individual failing to produce clotting factor VIII.
The recessive allele expresses an altered protein that doesn't function.
This increases clotting time, so person bleeds for a longer period of time.
So knocks can result in internal bleeding.
54
Treatment for haemophilia
Males with haemophilia have a near normal quality of life with an average lifespan of 10 years shorter than unaffected male.
55
Inheritance of haemophilia?
Males only have one X chromosome, so are hemizygous.
56
What is Nail Patella syndrome
Example of autosomal linkage?
Dominant allele, given letter N, that codes for protein involved in development of limbs in embryo.
Gene locus is on chromosome 9.
Gene locus is very close to ABO group gene so probably inherited together.
57
Symptoms of Nail Patella Syndrome
Underdeveloped kneecaps and nails, and inability to straighten elbows.
58
What is a model organism?
Species studied to enable scientists to understand biological processes.
Eg, Drosophila Melanogaster.
59
Why are fruit flies good model organisms?
- Have short generation time ( ~10 days) so many generations can be studied in short period of time
- Breed in large numbers
- Small size and low costs of care. (easy to breed)
- Detailed knowledge of their biology and genetics.
60
Requirements for using the chi squared test in genetics
large sample size
Only raw and categoric data
No zero values
61
Down's syndrome info?
Gamete has two copies of chromosome 21 (trisomy).
Zygote has 47 chromosomes.
(caused by translocation)
62
Turner's syndrome info?
Caused by non-disjunction during oogenesis. Gamete without sex chromosome (affects 23rd chromosome)
Only 45 chromosomes in zygote.
63
Physical signs of down's syndrome
Small ears, learning difficulties, decreased muscle tone at birth.
64
Physical signs of Turner's syndrome
Short stature
Elbow deformity
No menstruation
Low hairline
65
Physical signs of Klinefelter's Syndrome
Infertility
Reduced body hair
Osteoporosis
Tall stature
66
Klinefelter's syndrome info?
Only affects males
Caused by non-disjunction during spermatogenesis.
Results in oocyte being fertilised by sperm carrying both X and Y sex chromosomes, so child has extra sex chromosome XXY.
67
Sickle Cell anaemia info?
CODOMINANT disorder
Caused by base substitution mutation at single locus on chromosome 11.
Glutamic acid is replaced with valine.
Affects B ppc.
68
What does sickle cell anaemia cause?
Causes abnormal haemoglobin to become crystalline and less soluble. RBC becomes sickle shaped, so distorted, so useless at transporting O2, as the RBC get stuck in capillaries, so can't pass normally
69
Symptoms of sickle cell anaemia
Tire easily, severe anaemia, breathless easily.
70
What is a chromosome mutation
Change in number of chromosomes
| Change in structure of chromosomes.
71
Causes of chromosome mutations?
Translocation
| Non-disjunction
72
Translocation (Chromosome mutations) info?
Piece of chromosome breaks off and is transferred to another chromosome and reattaches.
Eg, Down's syndrome
Long arm of chromosome 21 breaks off and reattaches to 14, so extra chromosome 21 is produced.
73
Non-disjunction (chromosome mutation) info?
Homologous chromosomes fail to separate in meiosis I. (Ana)
OR
sister chromatids fail to separate in meiosis II. (Ana)
Gamete either has one more or one less chromosome.
74
What is inversion
Segment of the chromosome breaks off and is reinserted in the same place, but it reverse direction relative to the rest of the chromosome.
75
What is a nonsense mutation?
Triplet for aa is replaced with a triplet that is a stop codon. The ppc is truncated so doesn't function.
76
What is a missense mutation?
Triplet for aa is replaces with a triplet for a different aa. - ppc will have different primary, secondary, tertiary and quaternary structure.
77
What is a silent mutation?
The triplet for an aa is replaced with a triplet for the same aa. - ppc is unaltered.
78
What is a frameshift mutation?
A base within the triplet for aa is deleted/inserted so all triplets after this point are affected. ppc is altered.
79
What is a beneficial mutation?
Small mutation - improved ppc function. Natural selection will select individual with improved protein function, inc frequency of beneficial allele in pop.
80
What is a neutral mutation?
Mutation may result in no effect on the organism
81
How does the degenerate code reduce the effect of point mutation?
All aa, have more than one triplet coding for them, so some point mutations wont change aa that is added to ppc at that position.
82
What is genetic testing?
Assesses risk of child inheriting genetic disease.
Parental carrier testing.
Prenatal testing
Newborn screening.
83
What is a pedigree analysis?
Family history used to construct pedigree tree to calculate probability of having child with inherited disease.
