Genetics Flashcards
(112 cards)
1
Q
What is genetics?
A
The study of heredity
2
Q
What is genetic information carried in?
A
Genes
3
Q
What are genes carried on?
A
DNA double helix ( which forms chromosomes)
4
Q
Size order?
A
genes- DNA- Chromosomes
5
Q
What are the two types of human gametes?
A
Ova and spermatozoa
6
Q
What is a chromosome?
A
A strand of genetic material ( DNA)
7
Q
What is DNA?
A
A long molecule that is made up of thousands of segments called genes
8
Q
How many chromosomes does a human gamete contain?
A
23
When an ovym and a sperm unite the corresponding chromosomes pair up/
9
Q
How many chromosomes in a fertilised cell?
A
46 ( 23 pairs)
10
Q
Which chromosomes determine a person’s sex?
A
The two sex chromosomes of the 23rd pair
11
Q
In a female which are the sex chromosomes?
A
XX ( both of these are large chromosomes)
12
Q
In a male which are the sex chromosomes?
A
XY ( the Y is a smaller chromosome)
13
Q
What is the cell division process called which produces ova and sperm?
A
Meiosis
14
Q
What happens in meisosis?
A
Each of the 23 pairs of chromosomes in a cell splits.
The cell then divides and each new call receives on set of 23 chromosomes
15
Q
What are genes?
A
Segments of a DNA chain.
Genes are arranged in sequence on a chromosome
16
Q
What determines the properties of an organism?
A
The sequence of genes in a chromosome
17
Q
What is the gene locus?
A
The location of a specific gene on a chromosome
18
Q
Does the locus of each gene vary from person to person?
A
No it doesn’t vary.
This is what allows each of the thousands of genes in an ovum to join the corresponding genes from a sperm when the chromosomes pair up at fertilisation.
19
Q
What is the genotype?
A
The genetic constitution of a person
20
Q
What is the phenotype?
A
The detectable outward manifestation of a genotype
21
Q
What are DNA bases>
A
Adenine, Thyamine, Cytosine and guanine.
Arranged in an order that is unique for each person
22
Q
What is a genome?
A
One complete set of chromosomes containing all the genetic information for one person.
23
Q
What are some practical uses of genetic sequencing in healthcare?
A
Can test patients for specific gene errors.
E.G if a patient is at risk of developing colon cancer
or inviduals with a personal or family history of breasst or ovarian cancer.
24
Q
How many genes exist for every locus in an offspring?
A
Two ( as every parent contributes one set of chromosomes and therefore one set of genes) to their offspring.
25
What is an allele?
A variation of the same gene
26
if a person has identical alleles on each chromosome they are...
homozygous for that trait
27
If a person has alleles that are different on each chromosome they are...
heterozygous for that trait
28
What are polygenic traits
They require the interaction of more than one gene
29
What are the categories of trait?
homozygous ( identical alleles on each chromosome)
hetrozygous ( different alleles for that trait on each chromosome)
polygenic ( require the interaction of more than one gene)
30
What is a dominant gene?
On autosomal chromosomes, one allele may exert more influence in determining a specific trait.
31
What is a recessive gene?
On autosomal chromosomes ( non sex determining) one allele may be less influential
32
What are autosomal chromosomes
Non sex determining
33
How are recessive alleles expressed?
If both chromosomes carry recessive versions of the alleles?
34
Do males or females have less genetic material and why?
Males have less genetic material than females.
Because the Y chromosome is smaller than the X. Therefore, this means that only have one copy of most genes on the X chromome.
35
Can a male pass genetic material from his X chromosome to his sons?
No.
Because a man transmits an X chromosome only to his female children.
Male children receive a Y chromosome.
36
What does multifactorial inheritance mean?
Reflects the interaction of at least two genes and the influence of environmental factors
37
What is an example of a multifactorial trait?
Height
In general the height of an offspring peaks between the heights of the two parents.
However, nutritional patterns, healthcare and other environmental factors also influence development of such traits such as height.
38
What are some factors that may contribute to multifactorial inheritance?
```
use of drugs, alcohol or hormones by either parent
maternal smoking
maternal or paternal exposure to radiation
maternal infection during pregnancy
prexisting diseases in the mother
nutritional factors
general maternal or paternal health
maternal-foetal blood incompatibility
inadequate pre natal care
```
39
What are genetic defects?
Defects that result from changes to genes or chromosomes
40
What are the categories of genetic defects?
Autosomal
sex linked
multifactorial
41
What are teratogens?
Environmental agents that can cause structural or functional defects in a developing foetus. May cause spontaneous abortion, complications during labour and delivery or hidden defects in later development).
( infectious toxins, maternal diseases, drugs, chemicals and physical agents)
42
What is a mutation?
A permanent change in genetic material
43
How can mutations ( a permanent change in genetic material) arise?
exposure to radiation, certain chemicals or viruses
They can also happen spontaneously and can occur anywhere in the genome
44
What are some consequences of mutations?
May produce a new trait that can be transmitted to an offspring
no effect
change the expression of a trait
change the way a cell functions
some mutations can cause serious or deadly defects, such as congenital anomalies or cancer
45
What is an autosomal disorder?
An error which occurs at a single gene site on the DNA strand
46
How many sex chromosome and autosome pairs does each individual have?
1 pair of sex chromosomes
22 pairs of autosomes
Total: 23 pairs of chromosomes ( 46 chromosomes in total)
47
Are most hereditary disorders caused by autosomes or sex chromosomes and why?
Autosomal chromosome defects.
Because there are 22 pairs of autosome chromosomes compared to 1 pair of sex chromosomes.
48
What is a dominant transmission?
Affect male and female offspring equally
| Children with one parent affected have a 50% chance of being affected.
49
What is recessive inheritance?
Affects male and female offspring equally.
If both parents are affected then the offspring will be affected.
If both parents are unaffected by carry the defective gene each child has a 25% chance of being effected
If one parent is affected and the other isn't a carrier then none of the offspring will be affected but all will carry the defective gene.
If one person is affected and the other is a carrier then 50% of their children will be affected.
50
What are sex-linked disorders?
Disorders that are linked to genes on the sex chromosomes
51
Where are the genes for most sex linked disorders?
On the X chromosome.
Therefore, males are more commonly affected as they only have one X chrosome. In females ( x,x) the other X chromosome can overpower the gene on the other X chromsome and.
52
What are some examples of multifactorial disorders?
```
Cleft lip
Cleft plate
Congenital heart diseases
Anencephaly
Clubfoot
```
```
Type 2 diabetes
hypertension
hyperlipidemia
most autoimmune diseases
most cancers
```
Environmental factors most likely influence the development of multifactorial disorders during adulthood.
53
What causes congenital anomalies or birth defects?
Aberrations in chromosome structure or number
Include the loss, addition or rearrangement of genetic material
54
Do chromosome aberrations occur more during meiosis or mitosis?
Meiosis.
It's a more complex process.
Potential contributing factors- maternal age, radiation and use of some therapeutic or recreational drugs.
55
What is translocation?
The relocation of a segment of a chromosome to a non-homologous chromosome.
Occurs when chromosomes split apart and rejoin in an abnormal arrangement.
56
What is a monosomy?
A condition in which the number of chromosomes is one less than normal.
An autosomal monosomy is incompatible with life.
57
What is a trisomy?
The presence of an extra chromosome
58
What is mosicism
A mixture of both abnormal and normal cells ( two or more cell lines in the same person).
The effects depend on the number and location of abnormal cells.
59
What is disjunction?
Occurs during meiosis and mitosis.
How chromosomes normally separate
60
What is non disjunction?
During meiosis and mitosis the normal process of disjunction ( separation) causes an unequal distribution of chromosomes between the two resulting cells.
Incidence of this increases with parental age.
61
What is the total number of chromosomes in a fertilised cell?
46
23 pairs
In the nucleus of a fertilised cell
62
According to genetic theory, if a child has cystic fibrosis ( CF) this must mean...
Both parents must transmit the gene for F
The trait for CF is a recessive gene
63
The presence of an extra chromosome is called
trisomy
Results from non disjunction
64
What is the definition of a mutation?
A permanent change in genetic material
Can occur spontaenously or as a result to exposure to radiation, certain chemicals or viruses
65
What is a phenotype?
The outward, detectable manifestation of a person's genetic makeup or genotype
e.g brown eyes.
66
What is the sugar molecule of DNA called?
Deoxyribose
Made up of five carbon molecules ( what gives it it's pentagon shape)
67
What is the structure of DNA?
A pentose sugar ( five carbon atoms)
bound to a phosophate molecule
bound to one of four nucleotides ( nitrogenous bases- four types_
68
What is the backbone of the DNA double helix?
The sugar-phosphate backbone
The pairing of the bases is what gives it it's rung son the ladder
69
How many nitrogenous bases are there in DNA?
X4
Adenine
Thyamine
Guanine
Cytosine
Each bonds to it's complementary base
70
What forms the genetic code?
The sequence of the four bases
71
How many bases code for a specific amino acid?
Three
72
Which base bonds with adenine?
Thymine
There are always two bonds between these two nucleotides
73
Which base bonds with Guanine?
Cytosine
There are always three bonds between these two nucleotides
74
How many pairs of chromosomes in the nucleus of a somatic cell in the human body?
23 pairs
The total number of chromosomes is therefore 46.
75
Each chromosome consists of...
functional units called genes
76
Do chromosomes normally exist in pairs?
Yes.
One is contributed by male parent, the other by female parent.
77
Do gametes contain paired chromosomes?
NO.
They contain 23 unpaired chromosomes
78
FACT
A particular type of cell ( for example a lung cell) will only use certain parts of the genetic code ( the genome) in its nucleus to do its job
79
What are genes?
They are located on chromosomes and provide the instructions for the cells to build amino acids and hence form proteins.
80
What four molecules make up the genetic coe>
Adenine
Thymine
Cytosine
Guanine
The sequence of these bases is read in groups of three ( called a triplet or codon)
It's the various arrangements of codons that produce different amino acids to make up different proteins.
81
What is a mutation?
A permanent change in a base that is physically expressed.
82
Do all cells in the body contain an identical copy of the genome?
No.
Gametes have only half the genome.
Erythrocytes have no nucleus and therefore none of the genome.
All other somatic cells ( other than RBCs) contain a full, identical copy of the individual's genome.
83
What are male chromsomes?
XY
Since females carry only X chromsomes a mother will only ever donate X chromsomes to her offspring.
It is therefore the male partner who determines the gender of the offspring since males can donate either an X or Y chromosome.
84
What is an allele?
Each form of a gene
85
When is a dominant characteristic expressed?
If the dominant allele is present on one or both chromosomes in a pair
e.g the allele for brown eyes is dominant, where as the allele for blue eyes is recessive
86
What does homozygous dominant mean?
Means an individual has a dominant allele on both chromosomes in a pair.
Dominant alleles are represented by upper case letters
87
What does homozygous recessive means?
Means an individual has inherited two copies of a recessive allele.
Recessive alleles are represented by lower case letters.
88
What is a punnett square?
Shows possible genetic combinations.
89
Which chromosome carries sex linked genes?
Almost all are on the X chromosome and are recessive.
The Y chromosome is very small and therefore carries very little genetic information.
In males, sex linked genes behave like dominant genes because the Y chromosome is unable to counteract the negative effects of the recessive gene.
90
Why do females rarely suffer from colour blindness or haemophilia?
These are on sex linked genes.
The other X chromosome ( which is not normally affected) can balance out the bad gene on the other X chromosome.
Can't happen with XY as not enough genetic material on Y to balance it out. Therefore, males are more likely to be affected.
91
In mitosis how many daughter cells are produced?
2
92
In meiosis how many daughter cells are produced?
4
93
How many chromosomes will exist in a daughter cell of meiosis?
23 unpaired chromosomes.
Said to be haploid
The nucleus copies the 23 chromosomes but the cell then divides twice.
94
In what cells does meiosis occur?
Gametes. ( ova and spermatozoa).
The chromosomes are unpaired.
Only become paired when the sperm and egg cells meet up.
95
What is a genotype?
The combination of alleles that an individual possesses for a particular trait- such as eye colour.
96
Are dominant genes always expressed>
YES
The characteristic will always be expressed, even when there is only one copy of the dominant allele.
97
What is a gene locus?
The location of a specific gene on a chromosome
98
Does a gene locus vary between individuals?
No.
This allows accurate chromosome matching ( pairing) when the egg and sperm unite at fertilisation.
99
What is a zygote?
When two gametes meet.
A zygote has 46 chromosomes ( 23 pairs)
100
What does the term phenotype describe?
The physical trait produced by the alleles
When a dominant phenotype is expressed it is impossible to tell if it's a homozygous dominant or hetrozygous dominant trait.
101
What is a genome?
A complete set of chromosomes containing all the genetic information of an individual.
102
Is a genome unique to each invidual
Yes.
Identical twins are the exception.
It is the arrangement of the bases which makes the genome unique.
103
What does mitosis produce?
Genetically identical cells.
It produces two daughter cells that are an exact replica of the cell from which they were copied.
104
What processes is mitosis responsible for?
Growth, repair and replacement of cells
105
What is a mutation?
A permanent change in genetic material
106
Does a cell have the ability to correct a mutation?
Yes.
Every cell has the ability to detet and correct changes to the sequence of nucleotides bases as part of the cell cycle.
However, if a mutation is not detected and corrected, it may cause a different protein to be made which can induce a new, different and sometimes unwanted trait in the new cells.
107
What are some of the effects of mutations?
None
Sometimes, where new proteins develop that are undesirable, it can affect the cell function.
This in turn can have lethal effects, such as development of congenital abnormalities or cancer.
108
Can a gene exist in more than one form?
YES
Different alleles of the same gene can exist.
Each form of a gene is called an allele.
The order of bases in the alleles is very slightly different so they code for slightly different variations of the same characteristic.
E.G the gene that codes for blood groups has three alleles A,B, and O.
109
What is a person who is a carrier?
Hetrozygous for a genetic disease but does not suffer from the illness.
E.G me and A1ATD.
E.g cytsic fibrosis.
110
What is multi-factorial inheritance?
Interaction between two genes along with environmental influences.
e.g height, heart disease and a number of inherited cancers.
111
What is cytokinesis?
Final phase of cell replication.
The newly formed cell contents physically separates into two cells.
112
What are the names for the phases of mitosis and meiosis?
```
Interphase
Prophase ( doubling of DNA)
Metaphase ( Assembly in centre of cell)
Anaphase (separation of chromosomes)
Telophase
Cytokinesis ( in meiosis this phase happens twice)
```
