Topic 16) Inheritance

what is a monohybrid inheritance?

inheritance of a single gene (gene passed from one generation to the next) -> reproduction sexually = equal odds of either allele to gametes = nuclei of zygote, equal chance of zygote inheriting either allele from parent

what happens in a high tryptophan environment?

Tryptophan binds onto the TRP repressor protein, it changes shape so that it can bind to the operator, RNA polymerase cannot fit, no genes transcribed -> repressible enzymes (stops as binds to operator)

how do test crosses work?

Unknown individual is crossed w individual expressing a recessive phenotype (aa) -> resulting phenotypes of offspring provide info to suggest the genotype of the unknown individual

difference between heterozygous and homozygous alleles

When the two allele copies from parents are identical in an individual they are said to be homozygous (AA) When the two allele copies from parents are different in an individual they are said to be heterozygous (Ab)

what is a structural gene

a gene that codes for a protein that has a function within a cell (eg. F8 codes for protein Factor VIII)

what is a transcription factor

a protein that controls transcription of genes by binding to specific region of DNA to ensure genes are being expressed in the correct cells, time + level -> allow organisms to respond to their environment

The allele for grey body colour in a species of animal is dominant to white, and the allele for dark eyes is dominant to the allele for pale eyes. A. Using symbols G and g for alleles of coat colour and D and d for the alleles of eye colour, draw a genetic diagram to show the genotypes and phenotypes of the offspring would you expect from a cross between a homozygous grey animal with dark eyes and a homozygous white animal with pale eyes. B. If this first generation of offspring were bred together, what would be the expected phenotypes in the second generation of offspring, and in what ratios would they occur.

a. grey body, dark eyes x grey body, dark eyes = GgDd x GgDd Gametes = GD, Gd, gD, gd & GD, Gd, gD, gd B: expected phenotype ratios are therefore 9 grey body, dark eyes : 3 grey body, pale eyes : 3 white body, dark eyes : 1 white body, pale eyes.

What is Huntington's disease caused by

abnormal alleles of the HTT gene on chromosome 4 (codes for protein huntingtin involved in neuronal development) -> abnormal allele is dominant over the normal allele (if one abnormal allele present they will suffer) -> allele has many repeated CAG triplets in the nucleotide sequence of their HTT gene suffer from the disease

What is haemophilia caused by

abnormal alleles on F8 gene that codes factor VIII (coagulating agent) on X sex-chromosome: -> dominant H = normal factor VIII -> recessive h = lack of factor VIII

What is sickle cell anemia what are the features

abnormal haemoglobin in their red blood cells -> crescent-shaped blood cells, less O2 transportation -> frequent infections, episodes of pain and anaemia

describe the action of transcription factors

activate genes in the correct, order/time/cells/amount: - can form part of protein complex - bind to promotor - RNA polymerase binds to the promoter - transcription begins, gene expressed or stops -> can either increase or decrease transcription

how does the chi-squared test relate to the degree of freedom and null hypothesis?

- Critical value (DOF) at p at >0.05: statistically sig - smaller than DOF null hypothesis is accepted so there is no statistical dif bt observed + expected - larger than DOF null hypothesis is rejected there is a statistical dif bt observed + expected

What are the roles of transcription factors

- Determines the sex of mammal - Allows Reponses to environmental changes (by switching on correct gene to respond to change) - Regulate cell cycle, growth and aptosis - Hormone have effect through transcription factors

what are the results for test crosses for dihybrid cross

- If no offspring exhibit recessive phenotype for either gene unknown = both homozygous dominant (AA, AA) - if offspring exhibit recessive phenotype for one gene but not the other, unknown = heterozygous (Aa) or one gene and homozygous dominant (AA) for other - if offspring exhibit the recessive phenotype for both genes then the unknown both heterozygous (Aa, Aa)

Describe transcription factors in prokaryotics

- Regulatory gene codes for protein called a repressor - Repressor binds to the operator - RNA polymerase is unable to bind to promotor region Eg. No lactose to bind to repressor protein, binds to operator, RNA cannot bind Eg. Tryptophan binds to allosteric side of repressor protein, changes shape and binds to operator

what causes phenotypes ratios obtained in the offspring not to be the same as expected ratios?

- Small sample size: not enough data sets (n) - No random assortment - Genetically unique sperm and egg that fuse = random - Linkage groups are inherited together - Crossing over = recombinants, breaks linkage - Epistasis = gene impacts expression of another - Lethal genotypes, if offspring die to particular combination, phenotype impacted.

what are characteristics of sex-linked chromosomes

- if gene on X chromosome males (XY) have 1 copy -> two phenotypes: normal and disease - if gene on X chromosome females (XX) have 2 copies -> three phenotypes: normal, carrier and disease Two sex chromosomes (XX, XY) are not always alike: - not always same genes in same position - not always homologous eg. Y chromosome = shorter + X - fewer genes

what are the results for test crosses for monohybrid cross

- if no offspring exhibit the recessive phenotype: -> unknown genotype is homozygous dominant - if offspring have recessive phenotype: -> unknown genotype is heterozygous

Describe transcription factors in eukaryotics

- increase genome, high number of transcription factors - factors bind to promotor region of a gene - increase or decrease transcription of the gene (correct gene, correct time, correct extent) ○ Help RNA polymerase bind to promotor or prevent RNA polymerase from binding to promotor

what are the characteristics of homologous chromosomes

- same length - same centromere location - same genes in the same position (loci) -> but not always the same alleles - same shape helps them to line up alongside each other in meiosis

how to represent a sex linkage

-> alleles as superscript next to the sex chromosome Gene found on X chromosome has two alleles G and g -> Heterozygous female written as XGXg -> ales genotype would be written as XGY

difference between meiosis I and meiosis II

-> separates homologous chromosomes -> reduction division (diploid cell -> haploid cell) -> 2 diploid daughter cells -> crossing over occurs -> interphase occurs -> synapsis, bivalent formed -> separates sister chromatids -> 4 haploid daughter cells -> no crossing over -> no interphase

What is a homologous pair of chromosomes

1 maternal chromatid + 1 paternal chromatid in a pair -> replicate in interphase -> 2 sister chromatids for M/P -> two copies of every gene, different alleles

what is the mechanism gibberellin hormones influencing transcription factors

1. repressor protien DELLA is bound to transcription factor PIF = prevents it from binding to promoter of amylase = no transcription can occur for amylase 2. Gibberellin binds to a gibberellin receptor + enzyme starts to breakdown DELLA 3. PIF is no longer bound to DELLA protein so binds to promoter of the amylase gene 4. transcription of amylase gene + amylase made

what happens during meiosis I, metaphase I

1. Bivalents line up along the equator of the spindle -> chromosomes can independently orientate so it is random what side of the equator homologous pair lie -> 2^pairs = number of combinations possible -> eg. 23 pairs of chromosomes = 8million possibilities 2. spindle fibres attached to the centromeres

what happens during meiosis I, prophase I

1. DNA condenses making it visible as chromosomes 2. homologous chromosomes (maternal/paternal) pair up at synapsis and line side by side forming a bivalent 3. as they are close crossing over (exchange of genetic material) of non-sister chromatids occurs at chiasma 4. centrioles move to opposite poles + spindle forms 5. envelope breaks down + nucleolus disintegrates

What determines phenotype?

1. Genes (genotype) = gene codes for a protein and affects phenotype through a particular mechanism 2. Environment = diet, temp, O2, humidity, light, presence of mutagens = impact genes expressed

difference between the mitosis and meiosis cells?

1. Genetic diversity -> Mitosis: genetically identical -> Meiosis: not genetically identical 2. Chromosomes -> Mitosis: 2n = diploid -> Meiosis: n = haploid with homologous pairs 3. number of cells -> Mitosis: 2 -> Meiosis: 4

describe the genetic basis of the effects of sickle cell anemia

1. Homozygous (two abnormal alleles for HBB) -> only produce sickle cell anemia haemoglobin -> suffer from the associated symptoms 2. Heterozygous (one normal + abnormal allele) -> some normal haemoglobin + some sickle cell -> carrier of the allele but may have no symptoms

how to carry out a chi-squared test?

1. Null hypothesis (no dif bt observed + expected) 2. Find observed number of each phenotype 3. Expected ratio = 9:3:3:1 4. Expected number 5. O-E (find difference) 6. Square difference to get rid of negative values 7. Squared difference/expected value 8. Add Squared difference/expected value 9. see if X2 value is greater than critical = reject NH

Example using a dihybrid cross: heterozygous eg. pea colour (yellow = YY, Yy, green = yy) eg. pod shape (round pod = RR, Rr, pinched = rr) What happens when both parents have YyRr genotype (yellow peas, round pods). work out dihybrid cross

1. Write out genotype -> YyRr x YyRr 2. Write out gametes -> YR, Yr, yR, yr 4. Draw punnet square 5. Work out phenotype ratio -> 9/16 - yellow peas round pod (dominant) -> 3/16 - yellow peas pinched pod (D/r) -> 3/16 - green peas round pod (r/D) -> 1/16 - green peas pinched pod (r/r) = 9:3:3:1 ratio

what happens during meiosis I, telophase I

1. chromosomes arrive at opposite ends of dividing cell. 2. spindle fibres break down 3. nuclear envelope forms around the two groups of chromosomes 3. nucleolus generally reforms

what happens during meiosis I, cytokinesis

1. division of cytoplasm - animal (cell membrane -> cleavage furrow) - plant (vesicles from Golgi A gather along equator of spindle (cell plate) + merge with each other = new cell) 2. end product meiosis I: 2 daughter cells (diploid)

what is the structure of the lac operon

1. promoter for regulatory gene 2. regulatory gene lacI for lac repressor protein Lac-operon: 1. Promoter for structural genes 2. Operator 3. Structural gene lacZ codes for lactase 4. SG lacY codes permease (allows lactose in cell) 5. Structural gene lacA codes transacetylase

what happens to lac operon when lactose is absent in the medium that the bacterium is growing in

1. regulatory gene is transcribed + translated to produce lac repressor protein 2. lac repressor protein (1st site) binds to operator 3. RNA polymerase can't bind to promoter region 4. Transcription of structural genes doesn't occur 5. No lactase enzyme is synthesized

describe the metabolic pathway for producing melanin

1. tyrosine (amino acid) is converted to DOPA -> catalysed by the enzyme tyrosinase 2. DOPA converted to dopaquinone -> catalysed by the enzyme tyrosinase 3. Dopaquinone is converted to melanin tyrosine → DOPA → dopaquinone → melanin

what happens to lac operon when lactose is present in the medium that the bacterium is growing in

1. uptake of lactose by the bacterium 2. lactose binds to 2nd site on repressor protein, changing shape = cannot bind to operator 3. RNA polymerase able to bind to promoter region + transcription takes place 4. mRNA from the 3 structural genes is translated 5. Enzyme lactase made + lactose broken down

how does haemophilia relate to sex-linked genes?

Abnormal alleles on X sex chromosome so: -> males (XY): one copy of gene = has condition -> females (XX): can be heterozygous + not suffer from the condition but act as a carrier

describe how gibberellin hormones relate to transcription factors

Controls seed germination by stimulating synthesis of amylase by influencing transcription of amylase gene -> gibberellin hormone increases mRNA for amylase through the breakdown of DELLA protein

what happens during interphase?

DNA replication occurs making: - two complete sets of DNA/duplicated chromosomes (2 sister maternal and 2 sister paternal chromatids)

What are the different processes causing genetic variation within meiosis?

Different combinations of alleles in gametes from: 1. crossing over 2. independent assortment (random orientation) -> fertilization any male gamete can fuse with any female gamete to form a unique zygote

difference between dominant and recessive allele? eg. If for horses the allele A for a black coat is dominant and the allele a for a chestnut coat is recessive what are the following phenotypes from these genotypes? AA, Aa, aa

Dominant: always expressed in the phenotype -> expressed in both heterozygous + homozygous -> AA → black coat, Aa → black coat Recessive: only expressed in phenotype if no dominant allele is present -> homozygous (bb) -> aa → chestnut coat

what is a genetic diagram and a punnett square

GD: show how characteristics are inherited. eg. alleles can be recessive, dominant or codominant genes PS: used to predict genotypes from gametes to explain phenotypes (observable characteristics)

what are linked chromosomes

Genes located (loci) on the same chromosome and so are likely to be inherited together (as do not assort independently during metaphase I) Types: sex linkage and autosomal linkage

what is the TRP operon

Genes transcribed to form enzymes used to synthesise tryptophan (AA) (repressible enzyme - product binds to repressor + it represses the synthesis of the enzyme)

what is a genotype? what is a phenotype?

Genotype: alleles of a gene of that individual. -> either heterozygous or homozygous Phenotype: observable characteristics of an organism -> genotype affects their phenotype

what are inducible and repressible enzymes

Inducible enzymes: substrate induces synthesis of enzyme (only synthesised if substrate present) -> causing transcription of gene for the enzyme to start Repressible enzymes: presence of repressor protein represses the synthesis of the enzyme, binds to operator -> transcription of the gene for the enzyme to stop

What is albinism what are the features

Lack of pigment melanin in the skin, hair and eyes -> pale skin, pale hair, pale blue or pink irises in eyes -> poor vision, by rapid, jerky movements of the eyes

what are the genes that dictate the height of some plants?

Le gene with two alleles: Le and le -> dominant allele Le = tall plants -> recessive allele le = short plants (homozygous)

how does height determining genes (Le/le) relate to gibberellin

Le regulates production of enzyme involved in forming active gibberellin GA1 (hormone stimulating division + stem elongation) Recessive allele le results in non-functional enzyme -> single amino acid substitution (threonine -> alanine) -> change primary structure at the active site of enz -> w/o enzyme, no active gibberellin is formed

order of meiosis?

Meiosis I: early/middle/late prophase I, Metaphase I, Anaphase I, Telophase I, cytokinesis Meiosis II: Prophase II, Metaphase II, Anaphase II, Telophase II, cytokinesis

what happens during meiosis I, anaphase I

Microtubules pull homologous chromosomes in each bivalent to opposite spindles with centromeres intact -> holding two chromatids of one chromosome firmly

difference between monohybrid cross and dihybrid cross?

Monohybrid cross = 4 squares, single pair of genes responsible for 1 trait, parents differ by a single trait Dihybrid cross = 16 squares, two pairs of genes responsible for two traits, parents have 2 dif independent traits (eg. flower colour, stem length)

what is the process of meiosis

Nuclear division = haploid cells from diploid cells -> produces gametes used in sexual reproduction -> two divisions: meiosis I and meiosis II (prophase, metaphase, anaphase and telophase)

what is the: - Promoter - Operator - Effector - Repressor protein

P: region of DNA required to allow transcription of a gene to occur, where RNA polymerase will attach O: segment of DNA to which a repressor binds to inhibit the transcription of a gene E: substrate (eg. allolactose) RP: a protein that prevents the transcription of a gene by binding to a specific region on DNA

meiosis stages in photomicrographs how to distinguish?

PI: Homologous pairs of chromosomes are visible MI: Homologous pairs lined up side by side AI: Whole chromosomes pulled, centromere intact TI: 2 groups of chromosomes where nuclei forms CI: Cytoplasm dividing + CM pinch inwards = 2 cells PII: single chromosomes visible MII: whole chromosomes lined up at equator AII: Centromeres divide + chromatids pulled TII: Nuclei are forming around 4 groups CII: Cytoplasm is dividing = four haploid cells

difference between parental type and recombinant?

PT: offspring that show the same combinations of characteristics as their parents R: offspring that show different combinations of characteristics from their parents

In the Drosophila melanogaster fruit fly there is an autosomal linkage between the gene for the body colour and the gene for wing length. For the gene for the body colour, the allele for a grey body is dominant to the allele for a black body. For the gene for wing length, the allele for normal wings is dominant over the allele for vestigial wings If two heterozygous Drosphilia with grey bodies and normal wings are mated, work out the phenotype and genotype of the offspring. describe the ratio found

Parent: GgNn x GgNn Gametes: GN, Gn, gN, gn gametes resulting from autosomal linkage: GN, gn genotypes: GGNN, GgNn, GgNn, ggnn phenotype: 3:1 ratio for dominant:recessive -> if ratio not seen, crossing over has occured

Example using a monohybrid cross: Codominance Gene for blood type has three alleles: - A, a dominant allele produces blood type A - B, a dominant allele produces blood type B - O, two recessive alleles will produce blood type O Predictions when blood type A (IAIO) person is crossed with a blood type B (IBIO) person

Parental phenotype: Blood type A x Blood type B Parental genotype: IAIO x IBIO Parental gametes: IA or IO IB or IO Phenotypes in offspring - 1AB:1A:1B:1O Genotypes in offspring: 1IAIB:1IAIO:1IBIO:1IOIO

Example using a monohybrid cross: One of the genes for the coat colour of horses has two alleles: B, dominant allele produces a black coat when present b, recessive allele produces a chestnut coat (homozygous) What happens when heterozygous male is crossed with heterozygous female

Parental phenotype: black coat x black coat Parental genotype: Bb Bb Parental gametes: B or b B or b Phenotype's offspring - 3 black : 1 chestnut coat Genotype's offspring - 1 BB : 2 Bb : 1 bb

Example using a dihybrid cross: Horses have a single gene for coat colour that has two alleles: - B, a dominant allele produces a black coat - b, a recessive allele produces a chestnut coat Horses also have single gene for eye colour - E, a dominant allele produces brown eyes - e, a recessive allele produces blue eyes What happens when a horse which is heterozygous for both genes has been crossed with a horse that is homozygous for one gene and heterozygous for the other

Parental phenotypes: black coat, brown eyes x chestnut coat, brown eyes Parental genotypes: BbEe bbEe Parental gametes: BE or Be or bE or be bE or be Phenotype's offspring - 3 black coat, brown eyes : 3 chestnut coat, brown eyes : 1 black coat, blue eyes : 1 chestnut coat, blue eyes

Monohybrid example: Sex linkage Gene found on X chromosome codes for protein factor VIII needed to make blood clot. Two alleles for factor VIII, dominant F = normal factor VIII and recessive f = lack of factor VIII What happens when carrier female (XFXf) x normal male (XFY)

Parental phenotypes: carrier female x normal male Parental genotypes: XFXf XFY Parental gametes: XF or Xf XF or Y Phenotypes offspring - 1 female normal : 1 carrier female : 1 male haemophilia : 1 male normal Genotypes in offspring: 1 XFXF : 1 XFXf : 1 XFY : 1 XfY

Genes for tail length + scale colour have autosomal linkage Tail length has two alleles: - Dominant allele T produces a normal length tail - Recessive allele t produces a shorter length tail Scale colour has two alleles: - Dominant allele G produces green scales - Recessive allele g produces white scales What happens when heterozygous normal tail and green scales is crossed with a newt that has a shorter tail and white scales

Parental phenotypes: normal tail, green scales x short tail, white scales Parental genotypes: (TG)(tg) x (tg)(tg) Parental gametes: (TG) or (tg) x (tg) Phenotypes in offspring - 1 normal tail, green scales : 1 short tail, white scales Genotypes in offspring - 1 (TG)(tg) : 1 (tg)(tg)

Example using a monohybrid cross F2 generation: Green x Yellow pea pods form (Gg, Gg, Gg, Gg) all heterozygous and green pea pods. what happens to F2 generation genotype and phenotype (Gg x Gg)?

Parents phenotype: Green x Green Parents genotype: Gg x Gg Parental gametes: G g x G g (circle gametes) Draw punnet square (GG, Gg, Gg, gg) Phenotype: 3 green, 1 yellow (ratio 3:1)

Example using a monohybrid cross F1 generation: In pea pods dominant alleles for colour is green (G) and recessive is yellow (g). If green pea pod and yellow pea pod cross over. work out genotype/phenotype of F1?

Parents phenotype: Green x Yellow Parents genotype: GG x gg Parental gametes: Gg (circle gametes) Draw punnet square (Gg, Gg, Gg, Gg) Phenotype: all have dominant G so all green (100%) -> as F1 = all heterozygous

Rabbits have a single gene for ear length with two alleles: - D, a dominant allele that produces long ears - d, a recessive allele that produces shorter ears A breeder has a rabbit called Floppy that has long ears and they want to know the genotype of the rabbit either: DD or Dd Breeder crosses the long-eared rabbit with a short-eared rabbit (dd) What are the possibilities of genotype and phenotype

Possibility 1: dd x DD Phenotypes of offspring - all long ears, 100% Genotypes of offspring - 1 Dd Possibility 2: dd x Dd Phenotypes of offspring - long:short = 1:1 Genotypes of offspring - 1 Dd : 1 dd -> if at least one offspring with short ears = Dd -> if no offspring with short ears = DD

what happens during meiosis II, prophase II + metaphase II + anaphase II

Prophase II - nuclear envelope breaks down + chromosomes condense, spindle forms at right angle to old one Metaphase II - Sister chromatids line up in single file along equator of the spindle Anaphase II - Centromeres divide + single chromatids pulled to op poles = 4 groups of chromosomes = half number of chromosomes compared to original parent cell

what happens in a low tryptophan environment?

RNA polymerase binds to the promotor and begins transcription of the 5 genes that code for enzymes -> causing more tryptophan biosynthesis

Gene that dictates feather colour of has two alleles (R / r) : - Allele R codes for a pigment that produces grey feathers - Allele r doesn't produce a pigment = in white feathers Another gene = found to have an effect on feather colour + has two alleles (F / f) dominant F = stops grey predict possible phenotypes

RRFF white feathers RrFF white feathers rrFF white feathers RRFf white feathers RrFf white feathers rrFf white feathers rrff white feathers RRff grey feathers Rrff grey feathers

how are structural and regulatory genes related?

Regulatory + structural genes found close together -> regulatory genes control structural genes -> structural genes can group/cluster into an operon where all genes are controlled by the same promoter

define: - Synapsis - Bivalent - Chiasma

S: the pairing of homologous chromosomes B: maternal + paternal pair (2 chromosomes, 4 chromatids) C: position where non-sister chromatids of homologous chromosomes cross over each other

What is the lac operon

Set of genes in bacteria that controls the production of the enzyme lactase (inducible enzyme, synthesized if lactose/substrate is present)

What is the chi-squared test? What does it test?

Statistical test to see if there is a significant difference bt observed and expected values of alleles/phenotype -> completed when the data is categorical -> if statistically significant something else is happening

In a species of plant, the allele for tall stem is dominant (T) to short (t) The two alleles for leaf colour, giving green (G) or white (g) in the homozygous condition are codominant producing variegated leaves in the heterozygote A plant with tall stems and green leaves was crossed with a plant with short stems and variegated leaves. The offspring from this cross consisted of plants with tall stems and green leaves and plants with tall stems and variegated leaves in ratio 1:1. construct genetic diagram

T = tall t = short G = green g = white parental P: tall x green & short x variegated parental G: TTGG or TtGG x ttGg gametes: TG + tG or tg phenotype: TtGG: tall, green & TtGg: tall, varigated

what causes albinism

TYR gene on chromosome 11 codes for enz tyrosinase -> recessive allele present on geneTYR present -> causes lack of/inactive enzyme tyrosinase -> tyrosine cannot be converted into melanin

what happens during meiosis II, telophase II + cytokinesis

Telophase II - membranes form around each group chromosomes Cytokinesis - Cytoplasm divides as new cell surface membranes are formed creating four haploid cells Overall - 4 haploid cell from 1 diploid cell, not genetically identical to each other, same genes, different alleles

what is codominance? how is it symbolised? eg. how to represent blood types: A, B and O from gene I (I is the gene blood types are represented as and 3 alleles are A,B,O)

both alleles are expressed in phenotype at same time in heterozygotes eg. heterozygous express both alleles in phenotype. -> gene = capital letter, superscript for allele eg. I^A -> Allele A = IAIA or IAIO, blood type A -> Allele B = IBIB or IBIO, blood type B -> Allele A + B (heterozygous) = IAIB = AB -> Blood type O (IOIO) is recessive

what does crossing over do to linkages? how is this related to drosophila fruit flies

breaks linkage bt genes on same chromosome -> male = no crossing over occurs (parental types) -> female = crossing over occurs (recombinant)

explain the meaning haploid?

containing one complete (single) set of unpaired chromosomes (1 of chromosome pair). symbol: n eg. sperm/eggs: gamete gives 1 set chromosomes, involved in sexual reproduction

explain the meaning diploid?

containing two complete sets of chromosomes (not red blood cell). 2 copies of chromosome symbol 2n eg. body cells (contain the DNA necessary for protein synthesis and cell function)

What is a mutation

different alleles from unpredictable change - Base substitution (one base takes place of another) ○ Silent mutation, nonsense or misence - Base addition (bases are added to the sequence) - Base deletion (bases are lost from the sequence) ○ Can cause frameshifts ○ Can cause the formation of STOP codon

what is independent assortment? how does it increase genetic variation

different combinations of alleles in daughter cells due to random alignment of homologous pairs along the equator of the spindle during metaphase I To work out the number of chromosome possibilities: -> 2^pairs (eg. 23 pairs = over 8million combinations)

what is the 9:3:3:1 ratio

dihybrid cross, if two heterozygous parents for both genes are mixed, you will get 9:3:3:1 ratio for phenotype -> unless there is crossing over or autosomal linkage

What are multiple alleles?

existence of 3/more alleles of a gene possible for one individual trait. Eg. human blood groups A, B, AB, O -> polygenic test

What is a regulatory gene

gene that codes for a repressor/transcription protein to control the expression of another gene so correct genes are expressed in the correct cell at right time protein binds to receptor/operator, prevents RNA polymerase binding so no transcription can occur.

what is a sex linkage

genes found on a region of a sex chromosome that is not present on the other sex chromosome (F:XX M:XY) -> as inheritance of these genes is dependent on sex -> sex-linked genes are found on longer X chromosome

What is Huntington's disease What are the features

genetic disease that develops as a person ages (>30) -> neurological degeneration (Brains cells are lost) -> lose the ability to walk, talk and think, fatal

why is it good to control when enzymes are synthesized

it stops materials and energy from being wasted -> eg. using materials and energy to synthesize an enzyme when its substrate is not present and it can't carry out its function would be highly wasteful

What is haemophilia what are the features

lack of normal factor VIII preventing normal clotting -> ability of the blood to clot is severely reduced -> sex-linked condition (F8 located on X-chromosome)

what is crossing over? how does it increase genetic variation

new combination of alleles on two chromosomes 1. homologous chromosomes pair up = close proximity 2. non-sister chromatids cross over and get entangled -> crossing points called chiasmata 3. entanglement places stress on DNA molecules 4. section of a chromatid from one chromosome breaks and rejoins with chromatid from the other chromosome

What is a karyotype? how are they prepared?

number + visual appearance of chromosomes in the cell nuclei of an organism or species. prepared from cells stopped in metaphase as most condensed conformations.

what is an F1 generation?

offspring from homozygous recessive crossed with homozygous dominant genotype (parental generation) eg. homozygous brown, BB w homozygous white bb offspring = F1 generation = heterozygous (Bb)

what is an F2 generation?

offspring from two individuals crossing from the F1 generation (heterozygous). A test cross used to identify the genotype of the offspring (Aa or AA)

what is reduction division?

results in cells that have half number of chromosomes as the parent cell (46 -> 23 to ensure they are haploid) -> so when haploid cells fuse they form a diploid cell

Describe the repressor protein structure

two binding sites: operator and effector to bind -> O: prevents transcription of structural genes as RNA polymerase cannot attach to the promoter -> E: repressor protein shape distorts and it can no longer bind to the operator

what is a autosomal linkage?

two/more genes closely located on same chromosome, do no assort independently during meiosis. -> any chromosome that isn't a sex chromosome -> just two possible combinations of alleles -> genotypes into brackets eg. EEAA -> (EA)(EA)

what is an operon

unit formed by a group of genes (eg. structural) in prokaryotes that are controlled by the same promoter

what are test cross? When do you use them?

used to deduce genotype of an unknown individual that is expressing a dominant phenotype (AA or Aa) -> used to indicate if homozygous or heterozygous

what is an allele? how is this linked to a homologous chromosome?

variation of a gene (same gene different genetic code) --> changes in base pair codes, nucleotide sequence Allele A → black coat Allele a → chestnut coat

what is epistasis?

when two genes on different chromosomes (different loci) affect the same feature

how is sickle cell anemia caused?

β-globin found in haemoglobin coded gene HBB (found on chromosome 11) has abnormal allele -> amino acid substitution (CTT is replaced by CAT) -> change in AA seq (Glu is replaced with Val) -> abnormal β-globin polypeptide (dif structure/shape)