Genetics Flashcards
(105 cards)
0
Q
Define chromosomes, how many do humans have and how many genes on each. Genetic material…. (4)
A
- Long chains of DNA wrapped around a packaging protein forming rod-like/thread-like structures.
- Humans have 46
- Hundreds or thousands of genes on each chromosomes.
- Genetic material is formed in cell nucleus in the form of chromomes.
1
Q
Define DNA (3 - name, define)
A
- Deroxy-ribose nucleic acid
- Chemical which carries genetic info in nuclei of cells.
- Made up of phosphate units, sugar units and four types of bases.
2
Q
Define gene (2)
A
-Piece of DNA which codes for a particular protein and therefore a characteristic.
OR
-A section of DNA on a chromosome that provides instructions for the cell to make a protein.
3
Q
What does a chromosome consist of? (1)
A
Each chromosome consists of a DNA molecule that is tightly coiled around special packaging proteins
4
Q
When are chromosomes visible? (1)
A
During cell replication
5
Q
What’s the relationship between chromosomes and species? (1)
A
Each species has a fixed number of chromosomes in the body cells of all individuals.
6
Q
Do body cells (somatic cells) have an odd or even number of chromosomes? (1)
A
EVEN
7
Q
What’s a homologous chromosome pair, where do each come from + how many? (4)
A
- Two chromosomes that contain different alleles for the same gene
- Each maternal chromosome had a corresponding paternal chromosome. These matched pairs are called a homologous pair
- Chromosomes can be sorted into similar shaped pairs.
- 23 maternal chromosomes and 23 paternal chromosomes
8
Q
The two chromosomes of………. (characteristics)
A
…..a homologous pair carry genes for the same characteristics
eg hair colour, blood group.
9
Q
What is a Double Helix?
A
It’s the name given to the twisted ladder shape of the DNA
10
Q
What are hydrogen bonds?
A
attractive forces that hold the two strands of DNA together
A = T and C =- G <—– A and T have two hydrogen bonds and C and G have three hydrogen bonds
11
Q
What’s a nucleotide?
A
a UNIT built up of a base
a sugar
a phosphate group.
12
Q
What’s complementary base pairing?
A
Used to describe how the bases A always bonds with T and C with G.
13
Q
Why are chromosomes stained?
A
To show patterns of bands
14
Q
What’s a karyotype?
A
Homologous chromosomes (similar shape + size + bands) can be paired and numbered from largest to smallest to produce a diagram called a karyotype.
15
Q
Difference between a karyotype and genome?
A
In ONE cell (both same DNA material):
Karyotype: organised DNA material
X X X X X X X
X X X X X X X
X X X X X X X
Genome: the total genetic material in no specific order
+-)(+)&@+^#(%^&$
)@&(+#^$^+%%+
“<P|+)(&@&@+^
16
Q
What’s DNA? (3) [define, double helix and sides of ladder)
A
- DNA is a very long molecule that carries the genetic INSTRUCTIONS an organism needs to grow, function + reproduce.
- A DNA molecule is made up of two linked strands, twisted into a double helix
- Each side of the ladder is a chain of alternating sugar and phosphate units.
17
Q
What does a base (A, T, C or G) attach to in the DNA molecule?
A
Each sugar unit has one of the four bases attached to it.
18
Q
How are the two strands of the DNA linked?
A
Linked by attraction (hydrogen bonds) between complementary base pairs.
19
Q
How many base pairs (not bases) make up the DNA in a human cell?
A
Around 3 billion base pairs make up the DNA in a human cell.
20
Q
Define Genome
A
The full sequence of DNA of an organism is known as its genome (the genetic make-up of an organism)
21
Q
How many letters code for an amino acid?
A
3
22
Q
What’s genetic code?
A
The sequence (order) of the bases along the DNA molecule is the genetic code.
23
Q
What does the genetic code tell the cell?
A
The code tells the cell what proteins to make so that it can live, grow and divide.
24
What does every 3 base code for? (2)
A specific amino acid. (ATT = always PINK, CGT = always BLACK)
each triplet of bases along a gene codes for a specific AA
25
Why are proteins vital for life? (2)
-Form structures like skin, bone and hair
eg keratin in hair
-Make up enzymes which control the chemical reactions of cells
eg the enzymes pepsin, lipase and amylase are produced by cells to digest our food.
26
What are proteins made up of?
Hundreds or thousands of amino acid (AA) units
27
What does the sequence of AA units determine?
The specific role of protein
28
What do protein synthesis enzymes do?
They read the base sequence and assemble the AA of a protein (translation machines)
29
Define allele (2)
- Different version of a gene found at a particular location (locus) on a pair of chromosomes.
- Alleles are genes that occupy the same position on homologous chromosomes.
30
What do alleles code for? BUT.....(1)
The same characteristic (eg eye colour) BUT they have a slightly different order of bases causing different traits (eg brown eyes + blue eyes)
31
What do alleles produce amongst individuals?
Alleles produce VARIATION in individuals
32
Why do alleles occur in pairs?
Because chromosomes are paired, alleles occur in pairs.
33
What are used to represent the alleles of a gene?
Upper case and lower case letters
34
Define characteristic
An attribute of an individual that is coded for by an allele
eg eye colour
35
Define trait
the particular feature that is determined by an allele
| eg brown eyes, blue eyes
36
Difference between characteristic and triat?
A characteristic is a like a type of attribute that's CODED for by an allele, and a trait is the actual attribute that's DETERMINED by allele
37
What does each gene carry?
It carries the instructions for making a specific protein, which in turn determines a particular trait.
38
What can vary on a gene? What are they called? (2)
- The actual sequence of bases making up a particular gene can vary between individuals
- These variants of the gene are called alleles
39
What's a mutation?
A sudden, permanent change in a gene or a whole chromosome
40
What's the locus?
Genes for a particular characteristic are at the identical position (the LOCUS) on the same chromosome pair for individuals of that species.
41
How do new alleles result?
They result from a mutation in the DNA molecule and produce new variations
42
Difference between gene and allele?
Genes are the length of DNA that codes for a particular protein/characteristic while an allele is a particular form a gene.
43
What causes different traits to be observed?
The proteins made from each allele will be slightly different causing different traits to be observed
44
Mutations can be caused by.... (2)
- Exposure to chemicals or radiation
| - Error in the replication of DNA just before the cell divides.
45
Are mutations harmful or beneficial. Explain why. (2)
- Most are harmful as they code for modified proteins that don't function properly.
- Occasionally a mutation is beneficial, as it codes for a modified protein that functions better than the original.
46
When can the mutations NOT be inherited?
If mutation occurs in a BODY CELL then only those cells produced from this cell are affected. The mutation cannot be passed to offpsring.
47
When can a mutation be passed on to offspring?
If mutations occurs in GAMETES (sperm or egg) then the mutation can be passed on to offspring IF that particular gamete is fertilised.
48
What is the ultimate source of genetic variation?
Mutations as they can result in new beneficial alleles within a population.
49
What's a gamete?
A sex cell i.e. a sperm or egg (OVUM) in animals. Ovum and pollen in plants
50
What are gonads?
Sex organs (testes, ovaries)
51
Define dominant allele (2)
-The allele which will be expressed in the phenotype if it is present as either a single gene or as two genes
eg B
-Always expressed even if only one copy is present.
52
Define recessive allele (2)
-The allele which is only expressed if these are two such allels
eg b
-Only expressed if dominant allele is not present.
53
Define genotype (2)
-It's the specific pair of alleles that the organism carries for a particular trait.
-What genes you carry
eg BB or bb or Bb (homozygous vs. heterozygous)
54
Define phenotype (2)
-The expression of the genotype, this is what you look like
eg brown or blue eyes - if it's a visible trait.
-Physical expression of allele carried
55
The genotype determines....(2)
- Genotype determines the phenotype
| - Allele codes for specific protein (genotype) and then protein determines the trait (phenotype)
56
Define heterozygous (2)
-Having dominant and recessive allele
eg Bb
-They are 'carriers' in pedigrees
57
Define homozygous (2)
-A pair of alleles that are the same
eg BB or bb (homozygous dominant and homo recessive)
-Known as 'purebred' (i.e. they only pass on one type of allele to their offspring)
58
Define DNA replication
The process the cell uses to make a copy of its DNA
59
When does DNA replication start? What happens after? (2)
- Immediately before the cell divides.
| - At the end, each chromosome is duplicated - each copy having identical DNA.
60
Define mutation in reference to DNA replication
An error in duplicating the base sequence is called a mutation
61
Define mitosis.
Type of cell division that produced new body cells for growth, repair and replacement.
62
Put chromatid and centromere in a sentence
Each replicated chromosome is called a CHROMATID; these are held together by a body called the CENTROMERE.
63
Each new daughter cells is identical to the original parent cell in mitosis UNLESS
there has been a mutation during DNA replication
64
Define a diploid cell
2n = cell with the full complement of chromosomes (46 in humans)
65
Define a haploid cell
1n = cell with half the full complement of chromosomes (23 in humans)
66
What's a zygote?
A cell formed when a sperm cell fuses with an egg.
67
What's asexual reproduction?
When one individual creates a genetically identical copy of itself - reproduced by MITOSIS.
eg yeast, aphids
68
What are the advantages of asexual reproduction? (2)
It's fast and produces many offsprings
| -can take advantage of favourable environmental conditions.
69
What are the disadvantages of asexual reproduction? (3)
- No genetic variation
- population more susceptible to adverse environmental conditions
- Easier to wipe out species because they can't adapt and become immune to certain disease etc
70
What is meiosis?
The cell division that produced unique gametes used in sexual reproduction and involves two cell divisions to produce 4 haploid cells.
71
Where does meiosis occur?
In cells of reproductive organs - testes and ovaries (gonads)
72
When are the homologous pairs separated and when are the chromatids separated?
The homologous pairs are separated in the first division and chromatids in the second.
73
What is Synapsis?
When pairs are lined up in the 1st division of meiosis, the chromosomes can cross over each other and some DNA is exchanged between them.
74
What is shuffling? (2)
- Which chromosome of each pair ends up in which cell is random.
- This shuffles the maternal and paternal chromosomes to give new combinations of combinations of chromosomes in gametes
75
What is fertilisation? (2)
- Male sex cell (gamete) combines with a female sex cell (gamete) to form a zygote.
- Gametes (eggs and sperm) fuse at fertilisation to form a zygote, restoring the full number of chromosomes.
76
Fertilisation + Variation, how is variation created in fertilisation? (2)
- Which two gametes fuse is random so offspring vary
| - Each zygote has a unique set of alleles (half = maternal and half = parternal)
77
What is sexual reproduction?
Reproduction producing two parents, where the offspring has some features inherited from each.
78
What is monohybrid cross?
A straight-forward cross involving only one gene with a pair of allels.
79
Sex is determined by?
X and Y chromosome (pair #23)
Though they are different, they pair up and are separated in meiosis
XX = Female
XY = Male
80
After meiosis, how may X an Y chromosomes in males + females?
A female's eggs only contain X
| Half of male's sperm contains X and half Y
81
What does genetic variation ensure?
What does variation mean with relation to survival?
What do survivors do?
(3)
- Helps to ensure survival of species
- Variation means that some members of a species are likely to survive changes in conditions
eg: change in climate or food supply or if a new disease develops
- Survivors reproduce to continue the species
82
How is variation caused?
Variation between individuals is caused by differences in their genetic code.
83
What's continuous variation? (2)
-Controlled by several genes
-Range of values showing a bell shaped or normal distribution when graphed (eg height or hand span)
_____
/ \
/ \
/ \
------------------------------
84
What is discontinuous variation? (3)
- Controlled by one gene with two different alleles
- One value or another/either or
- Do not show a range
eg: tongue rolling, free or fixed earlobes, hitch hikers thumb
85
What is Monohybrid inheritance? (2)
- Involves the inheritance of a single characteristic (and trait) that is controlled by one gene with two alleles.
- An individual inherits two of these alleles from its parents at fertilisation.
86
What does a Punnet Square show?
It shows all possible gamete combinations in a cross of parents, giving the expected genotype and phenotype ratios of offspring.
87
What is test cross used for?
A test cross is used to determine whether an individual with an unknown genotype is homozygous dominant or heterozygous for a particular trait.
88
What do you do in a test cross? (2)
Cross unknown genotype with homozygous recessive
-IF a recessive offspring, unknown was heterozygous
-IF ONLY dominant offspring, unknown was homozygous
dominant.
89
What does a pedigree chart show?
Shows the inheritance of a single genetic trait over several genertations.
90
How are mating couples connected and how are offspring connected?
Mating couples are connected by horizontal lines and offspring are placed on branches below.
91
What can a pedigree chart be used to determine? (3)
- Genotype and phenotype of family members
- Whether an allele is dominant or recessive
- The probability of a child inheriting an allele or trait.
92
What can a pedigree chart be used to determine (inheritance patterns) (3)
Inheritance Patterns:
- The most common trait is NOT necessarily the dominant one.
- Two recessive crossed to produce ONLY recessive offspring
- Two dominants crosses can produce BOTH dominant and recessive offspring IF both parents heterozygous
93
What's genetic variation?
Refers to a variety of different genotypes for a particular trait within a population
94
What's natural selection?
Organisms with characteristics best suited to their environment become more successful, and so expand in numbers
95
What is phenotype ratio?
A prediction of the phenotypes and their occurrences as a result of a cross.
96
Variation exists......
....in the traits of individuals of a population
97
Two types of Variation: (2)
-Some of this variation is GENETIC due to different alleles carried by particular individuals
eg white coal allele
-Some of this variation is ACQUIRED due to the environmental effects and/or the effect of an individual's actions.
eg overfed domestic rabbit, stunted plant growth due to lack of nutrients
98
What is inheritable variation?
Genetic variations can be passed to next generation
99
What is non-inheritable variation?
Acquired variations cannot be passed on (eg cutting off a limb)
100
What does genetic variation result in?
Results in a variety of phenotypes with a population
101
New phenotypes appear.......
New phenotypes appear within a population as mutations introduce new alleles and sexual reproduction (crossing over etc) results in new combinations of alleles
102
When will a population as a whole survive longer?
If population is more genetically diverse, it will survive bad conditions etc
103
Some phenotypes are better........
Individuals with these........
....suited to changes in environment (eg extreme drought, new predators, new diseases), factors that act as SELECTION PRESSURES
......better adapted phenotypes will live longer and product more off spring with favourable alleles
104
Natural Selection: (2)
- Selection pressures over many generations result in favourable phenotypes surviving, reproducing and increasing in frequency.
- Other, less favourable phenotypes decrease and sometimes die out. Thus the phenotype ratio is changed.
