16) Inheritance Flashcards
1
Q
define homologous pairs of chromosomes
A
- same genes located at the same loci
- same size/length
- same shape/ position of centromere
- same banding pattern
2
Q
what type of chromosomes are homologous
A
autosomes (chromosome pairs 1-22)
3
Q
what type of chromosomes are not homologous
A
sex chromosomes (pair 23)
4
Q
what is haploid
A
- ONE complete set of chromosomes
- n (number of) chromosomes
- not in homologous pair
- each chromosome diff in size/shape/genes
5
Q
what is diploid
A
- TWO complete sets of chromosomes
- 2n chromosomes
- eg: humans 2x23 = 46
6
Q
why must no. of chromosomes be halved before fertilisation / the need for reduction division
A
- to maintain chromosome diploid number
- from parents to offspring
- to give genetic variation in gametes
- too many extra sets of chromosomes cause problems
- reduction division produces gametes
- gametes fuse to form zygote
- zygote has maternal & paternal chromosomes
- gametes are haploid
- so zygote is diploid
7
Q
what is bivalent
A
a pair of homologous chromosomes
8
Q
what is chiasma
A
point at which crossing over occurs
9
Q
describe prophase I
A
- chromosomes condense
- homologous chromosomes pair up = bivalents
- crossing over
10
Q
describe metaphase I
A
- spindle fibres attach to centromeres
- homologous pair of chromosomes (bivalents) line up at the equator
- random assortment of bivalents
11
Q
describe anaphase I
A
- spindle fibres contract to pull centromeres towards pole
- one of each pair of chromosomes to either end/pole
12
Q
describe telophase I
A
- chromosomes reach the opposite pole
- chromosomes decondense
13
Q
describe prophase II
A
- spindle reforms
14
Q
describe metaphase II
A
15
Q
describe anaphase II
A
16
Q
describe telophase II
A
- spindle disassemble
17
Q
what is meiosis II
A
identical to mitosis, except there are 2 cells
18
Q
what are ways in which meiosis increases genetic variation
A
- crossing over
- independent/random assortment
- random fusion of gametes
19
Q
how does crossing over increase genetic variation
A
- during prophase I
- crossing over between non-sister chromatids
- non-sister chromatids have diff combo of alleles
- exchange alleles
- chromatids have new combo of alleles
- linkage groups broken
- gametes have unique combo of alleles
- fusion of gametes
20
Q
how does random/independent assortment increase genetic variation
A
- during metaphase I
- homologous chromosomes randomly align along the equator
- independent of each other
- this leads to diff combos of chromosomes in daughter cells
- results in new combos of alleles
21
Q
what is random fusion of gametes
A
any male gamete can fuse with any female gamete
- random combination of chromosomes generated
22
Q
define gene
A
sequence of DNA that codes for a polypeptide
23
Q
define locus
A
specific position of a gene on the chromosome
24
Q
define allele
A
a version of a gene
25
define homozygous & heterozygous
- homozygous = alleles on each homologous pair is same
- heterozygous = alleles on each homologous pair are different
26
define dominant & recessive
- dominant = phenotype expressed even if only one is present (heterozygous) + homozygous, it overrides the recessive
- recessive = phenotype only expressed if homozygous
27
define codominant
both alleles expressed in phenotype
28
define linkage
genes that are close together on the same chromosome
(unlikely to be separated during crossing over)
- GENES ON THE SAME CHROMOSOME
29
define test cross
testing suspected heterozygote w known homozygous recessive
30
define F1 & F2
F1 = first generation (of offspring by parents)
= parents homozygous
= F1 heterozygous
F2 = second generation (offspring's offspring)
31
define phenotype
observable features of an organism (eg: brown)
32
define genotype
alleles an organism possesses (eg: Bb)
33
define sex-linkage
genes found on the X or Y chromosome
34
why is the chi-squared test used ?
to test whether the difference between the observed & expected frequencies is significant/ or whether difference is due to chance
35
state the number of phenotypes that each genetic cross produces
monohybrid = 2
codominant = 3
multiple alleles = 4
36
state the ratio for heterozygous x homozygous recessive in a dihybrid cross
1:1:1:1
37
state the ratio for heterozygous x heterozygous in a dihybrid cross
9:3:3:1
38
if the critical value is greater than 0.05, the null hypothesis should be...
REJECTED
39
if the critical value is less than 0.05, the null hypothesis should be...
ACCEPTED
40
what does the null hypothesis state?
there is NO significant difference between the observed & expected results
41
what is the gene, enzyme, type of disease for Albinism
- TYR
- tyrosinase enzyme
- autosomal recessive
42
what is the gene, enzyme, type of disease for Huntingtons
- HTT
- huntingtin
- autosomal dominant
43
what is the gene, enzyme, type of disease for Sickle cell anaemia
- HBB
- haemoglobin
- co-dominant
44
what is the gene, enzyme, type of disease for Haemophilia
- F8
- factor VIII
- sex-linked (x linked recessive)
45
symptoms & treatment for albinism
- pale/white skin, hair
- pink eyes
- increased susceptibility to sunburn/skin cancer
- rapid/jerky eye movements
- poor vision
- stay in the shade/spf/hat
- monitor skin
46
symptoms & treatment for Huntington's
- involuntary movements/uninhibited motor control
- progressive mental deterioration
- brain cells lost
- symptoms come at 30+ --> fatal
- drugs to control movements (tetrabenazine)
47
symptoms & treatment for Sickle cell anaemia
- haemoglobin less soluble
- lack of RBCs
- less oxygen to organs
- RBC get stuck in capillaries % block blood flow
- causes pain
- protection against malaria
- stem cell transplant
- blood transfusions
- medicine
48
symptoms & treatment for Haemophilia
- excessive bleeding
- large bruises
- internal bleeding
- regular injections of clotting factor medicine (curable)
49
differences between structural & regulatory genes
structural
- EG: lac z/y/a
- codes for structural protein (eg: amylase)
- needed for structure/function of cell
regulatory
- EG: lac repressor/DELLA repressor
- code for regulatory proteins
- controls gene expression
- codes for transcription factor
- binds to promoters
- allows/stops binding of RNA polymerase
50
differences between repressible & inducible enzymes
repressible
- produced continuously
- synthesis can be prevented by binding of repressor protein to specific site
- the thing that codes for this enzyme activates repressor/ allows repressor to bind to operator & stops gene expression
inducible
- synthesis only occurs when substrate present
- transcription of gene only occurs when substrate binds to TF
- eg : lactose permease
51
what are transcription factors
- proteins that bind to DNA
- bind to promoter
- allows RNA polymerase/other TFs to bind to promoter/DNA
- controls gene expression
- so that genes are expressed at the correct time/order/context/cell type
52
how does gibberellin activate genes
- DELLA proteins inhibit transcription factor
- gibberellin binds to receptor
- in aleurone layer
- DELLA proteins broken down
- TF binds to promoter region
- transcription of gene coding for amylase
- translation
53
how do multiple alleles arise
- gene mutation
- change in bases by deletion/substitution/insertion
54
what does lacZ code for? & whats its role
B-galactosidase / lactase - hydrolyses lactose into glucose + galactose
55
what does lacY code for? & whats its role
lactose permease - makes membrane more permeable to lactose
56
Explain why a person who is homozygous recessive for the TYR gene shows albinism [3]
- recessive mutation
- no melanin
- pale hair/skin, pink eyes
57
Explain how the lele genotype and its gene product results in dwarf plants [3]
- homozygous recessive
- lele codes for non-functional enzyme
- no active gibberellin
- less cell elongation
58
how DELLA proteins act as repressors preventing gene expression
- bind to transcription factor
- TF cannot bind to DNA/promoter
- RNA polymerase cannot bind to promoter
- no transcription/mRNA not made
59
Using haemophilia as an example, explain the relationship between a gene, a protein and a phenotype [5]
- gene codes for a protein which determines the phenotype
- F8 gene
- located on X chromosome (sex-linked)
- non-functioning factor VIII
- so excessive bleeding/blood does not clot quickly
- X^H X ^H = normal female
60
what is gibberellin
cell signalling molecule/ hormone
61
what is the role of gibberellin
- cell elongation
- so plant/stem grows longer
62
suggest explanations for the 9:3:3:1 ratio
- fewer recombinants
- linked genes/ genes on same chromosome
- alleles inherited together
- no independent assortment
- crossing over produces recombinants
- during meiosis (prophase I)
63
why do two genes assort independently
- because they are not linked/on separate chromosomes
- so each homologous pair of chromosomes orients itself separately
- in metaphase I of meiosis
- gives 4 new combinations
- parental allele combinations are not fixed
64
division of the cytoplasm
cytokinesis
65
outline the main features of the lac operon
- promoter
- operator
- 3 structural proteins (lacY, lacZ, lacA)
66
role of regulatory gene in lac operon
- always expressed
- controls structural gene expression
- codes for repressor protein
- repressor blocks promoter by binding to operator
- prevents RNA polymerase binding to promoter
- lactose binds to repressor
- so repressor cannot bind to operator/ gene expression can occur
67
advantages of repressible enzyme
- made continuously
- because necessary for cell
- made until product concentration too high
68
explanations for unexpected results
- mutation
- crossing over
- linkage
- epistasis
- environmental affects
- small sample size
69
how does the expression of the TYR gene lead to the production of melanin
- TYR codes for tyrosinase
- converts tyrosinase to DOPA
- converts DOPA into dopaquinone
- dopaquinone converted into melanin
TYR --> tyrosinase --> DOPA --> dopaquinone --> melanin
70
Suggest why structural genes in operons are transcribed together
- share one promoter
- all proteins work together
71
Explain how a mutation of the TYR gene can result in albinism
- substitution / deletion / insertion
- change in primary / secondary / tertiary, structure of protein
- stop codon
- (so) no / inactive tyrosinase produced
- tyrosine not converted to DOPA / dopaquinone
- melanin not formed
72
Explain how a gene mutation can lead to iduronate 2-sulfatase not functioning properly or not
being produced
- base / nucleotide, insertion / deletion / substitution
- frameshift / changed reading frame
- stop codon
- changes / different, primary structure / amino acid sequence
- changes / different, folding / 3D shape / 3D structure, of enzyme / protein
- active site does not, bind / fit, substrate / complex molecules
