Inheritance 2 Flashcards

Question

Apart from meiosis what can also cause genetic variation?

Answer 1

Besides meiosis, fertilisation can also cause genetic variation! This is due to: 1. Random mating 2. Random fusion of gametes

Answer 2

Genotype: the alleles possessed by an organism * Represented by same alphabet (e.g. B and b=same gene, different allele) *gene short form name is usually in italics, whereas gene full name and protein is not italicized (e.g. HBB=haemoglobin beta gene➡️codes for beta globin protein)

Answer 3

Phenotype: the observable characteristics of an organism ➡️ can be influenced by genotype, environment

Answer 4

*Expressed in the phenotype even when only one copy of the allele is present *Expressed in heterozygous and homozygous for the allele (e.g. Bb and BB)

Answer 5

*Expressed in the phenotype only when two copies of the allele are present *Expressed only in a homozygous form the allele (e.g. bb)

Answer 6

1) parental phenotypes (don’t forget the X in between them) 2) Parental genotypes 3) Gametes (should be circled) 4) Offspring (F1) genotype and phenotype (you must draw this in a punnet square) 4) Probability/ratio depends on what the questions wants

Answer 7

Test cross=method to determine exact genotype of a dominant phenotype organism ➡️Is it homozygous dominant or heterozygous for the gene? ➡️Cross with individual homozygous recessive for the gene For example : how to determine if genotype is TT or Tt? Cross with tt

Answer 8

A cross of same purebred organisms always produce offspring with the same genotype. Homozygous individuals.

Answer 9

Parental (P) generation=initial generation

Answer 10

Result of crossing 2 different purebreds (i.e. 2 homozygous of different phenotype.) F1 offspring are all heterozygotes. Stands for first filial generation/first set of offspring

Answer 11

Offspring results of self pollination of F1 plants OR cross of 2 heterozygotes.

Answer 12

*Involves the crosses of two genes at once ➡️ 2 genes are on different chromosomes ➡️ 2 alleles each ➡️ Code for different traits For example gene for tall/short plants and gene for purple/white flowers 9:3:3:1 ratio

Answer 13

Law of segregation: during gamete formation, the alleles for each gene segregate from each other (during anaphase I) so that each gamete carries only one allele for each gene. Law of independent assortment: Each pair lines up independently of others in equator (during metaphase I). Genes for different traits can segregate independently during the formation of gametes. Law of dominance: some alleles are dominant while others are recessive; an organism with at least one dominant allele will display the effect of the dominant allele.

Answer 14

*Sex-linkage=allele/gene carried on the sex chromosomes *Usually X chromosome *Y chromosome is shorter than X ➡️Carries fewer genes than X ➡️Do not have the same genes in the same loci ➡️Some different genes from X ➡️Some genes exist as a single copy only either on X or Y chromosome= hemizgous Types of sex-linked inheritance patterns: *X-linked recessive *X-linked dominant

Answer 15

*Phenotype determined by recessive allele on X *Phenotype will be expressed if there are no dominant alleles of the same gene present *I.e. in females with both recessive alleles on X, or males with one recessive allele on X *To show genotypes for sex-linked genes: a) Use symbols for gender (XX-female, XY-male) b) Write alleles as subscripts

Answer 16

*Phenotype determined by dominant allele on X *Phenotype is shown in homozygous dominant and heterozygous females, and males with the dominant allele *Affected males will not pass the dominant allele on X to sons (since sons must inherit Y) *But will pass it on to daughters (Daughters must inherit one X from mum and one X from dad)

Answer 17

In a pedigree diagram: ⚪️ is female ⬜️ is male ⚫️ and ⬛️ is affected

Answer 18

*Codominance=when both alleles are fully expressed in the heterozygote *More than 2 phenotypes are possible *Phenotype of heterozygote different from either homozygote *When 2 heterozygote (F1) are crossed, the resulting phenotype is 1:2:1 ratio

Answer 19

Genes with more than 2 alleles E.g. ABO gene for human blood groups *I^A=A allele ➡️Codominant *I^B=B allele ➡️ Codominant *i = O allele ➡️ recessive to I^A and I^B

Answer 20

AKA epistasis *When different genes at different loci *Interact to affect ONE phenotype

Answer 21

Linked genes: 2 genes are in the same chromosome ➡️ They are in an autosomal linkage group (not to be confused with sex/autosomal-linked genes!) ➡️Likely to be inherited together ➡️No independent assortment ➡️ No separation during anaphase The closer the loci are the lower the chance of crossing over. We will use brackets in genotypes for example: (EA)(EA) to show they are on the same chromosome. EEAA without brackets indicates they are on the different chromosomes.

Answer 22

Cross an individual heterozygous for both genes (EA)(ea) with a homozygous recessive individual (ea)(ea). In dihybrid the ratio will be 1:1:1:1 In autosomal linkage the expected ratio is 1:1 But getting a 1:1 ratio is rare 1:1 ratio = total linkage Linked genes can be separated by rare cross over events during prophase I. The closer the loci are the lower the chance of crossing over

Answer 23

Cross over value= measure of distance between 2 gene loci on chromosomes This is the percentage that belongs to the recombinant class The smaller the value, the closer the loci are together The closer the loci are together the lower the chance of crossing over.

Answer 24

Inherited blood disorder Affects the structure of haemoglobin Cause: base substitution in gene coding for beta globin Base substitution (T is replaced by A) in gene coding for beta globin results in ➡️different mRNA codon ➡️ different tRNA brings a different amino acid to ribosome ➡️Leads to a change of 6th amino acid in polypeptide chain ➡️ altered primary structure ➡️ glutamic acid is polar whereas valine is non-polar ➡️ changed secondary, tertiary and quaternary structure

Answer 25

*Hb^A=Normal B-globin allele *Hb^s=Mutant B-globin allele *Hb^AHb^A=2 normal B polypeptide alleles *Hb^sHb^s=2 mutant B polypeptide alleles (sickle cell anaemia) *Hb^AHb^s= 1 normal and 1 mutant Has the sickle cell trait/"carriers" Half of the haemoglobin is normal Codominant

Answer 26

*Classic form caused by autosomal recessive mutation *Melanin is missing from eyes, skin and hair Symptoms: *Pale/white skin and hair *Pink eyes *Increased susceptibility to sunburn/skin cancer *Rapid, jerky eye movements *Tend to have poor vision *Tend to avoid bright light

Answer 27

*Classic form caused by autosomal recessive mutation *In TYR gene coding for enzyme tyrosinase *Involved in conversion of tyrosine to DOPA and DOPA into to dopaquinone, which is needed for melanin production in melanocytes (cells that produce melanin).

Answer 28

Tyrosinase is an oxidase enzyme Has two copper atoms, binds 1 O2 molecule Transmembrane protein found at membrane of melanosomes (large, specialised organelles in melanocytes) Tyrosine→DOPA→dopaquinone→melanin Tyrosinase is needed to convert tyrosine to DOPA and DOPA to dopaquinone. Mutation results in absence/inactive tyrosinase

Answer 29

*Sex-linked *Gene for blood clotting protein (factor VIII) is carried on X chromosome *Caused by X-linked recessive mutation *X^H=normal allele *X^h=haemophillia allele →Factor VIII (8) is not produced →This reduces clotting of blood Symptoms: *Excessive bleeding *Bleeding into joints *Large bruises *Internal bleeding

Answer 30

*Neurological disorder (i.e. neurones die) *Usual onset in middle age btwn 28-65yo *Caused by an autosomal dominant mutated allele *Mutation at the Huntingtin (HTT) gene on chromosome 4 Symptoms: *Involuntary movements/uninhibited motor control *Mood changes *Progressive mental deterioration *Brain cells lost

Answer 31

*Normal recessive allele has 10-35 repeats of CAG *Mutant dominant allele has equal to or greater than 36 repeats of CAG →CAG codes for glutamine/polyglutamine →Huntingtin protein misfolded *More repeats=earlier onsets →E.g. onset even in babies if many repeats

Answer 32

*Inherited genetic disease *Faulty, autosomal recessive allele of the CFTR gene Symptoms: *Thick and sticky mucus produced at lungs *Mucus not moved effectively by cilia→mucus accumulates *Mucus traps bacteria →more infection *Reduced gaseous exchange→due to longer diffusion pathway *Diffuculting in breathing, wheezing *coughing→ cause lungs to be scarred *blocked pancreatic duct→reduced digestion, damage of pancreatic tissues causes diabetes *Blocked sperm ducts/oviducts →reduced fertility

Answer 33

Faulty, autosomal recessive allele of the CFTR gene Normal CFTR protein: *Transmemebrane protein at cell surface membrane *Acts as chloride channel *Has binding site for ATP *Cl- moves out of cell via active transport *Water is drawn out from cell →Normal/less viscous mucus formed Faulty CFTR allele: a) Base deletion→faulty CFTR (most common) b) Base substitution → STOP codon →Incomplete CFTR Faulty CFTR protein: *No functional channels for Cl- ions. *Cl- ions do not move out *less water leaves cell →Formation of thick, sticky mucus on cell surface membrane

Answer 34

Gene expression is the process where gene is being transcribed to mRNA and then translated to protein.

Answer 35

Gene regulation/control is the process that enables gene expression in specific cells and specific time. ➡️to ensure gene is expressed in correct cell at the correct time in the correct context. ➡️Some genes are transcribed all the time to produce constitutive proteins ➡️Others are only “switched on” when their protein products are required ➡️why? ⚪️No wastage of energy and recourses ⚪️ No expression of protein that may interfere with cell function

Answer 36

⚪️ Gene that code for proteins needed for cell structure or function ⚪️ E.g. proteins that form part of cellular structure, enzymes rRNA etc

Answer 37

⚪️Genes that code for regulatory proteins that controls gene expression/ transcription ⚪️E.g. transcription factors, including repressions and activators Transcription factors can bind to a specific DNA sequence and control gene transcription ⚪️Activators=increase gene expression ⚪️Repressor=reduce/inhibit gene expression (bind to operator)

Answer 38

A repressible enzyme is one whose synthesis can be prevented when a repressor protein binds to an operator, a specific sequence of DNA. Repressor stops binding of RNA polymerase.

Answer 39

An enzyme whose synthesis only occurs when a substrate is present. Inducer that binds to a regulatory protein . ➡️ gene is switched on. E.g. lac enzymes

Answer 40

Gene control in prokaryotes: operons ⚪️ Found in prokaryotic DNA ⚪️Makes up a unit of gene expression in bacterium ⚪️Regulatory gene is close to the operon Operon consist of: ⚪️One or more structural genes, under control of a single promoter ⚪️Control region of DNA, which are specific sequence recognised by regulatory proteins and enzymes ⚪️Promoter=where RNA polymerase binds ⚪️Operator=where repressor binds

Answer 41

⚪️Found in Escherichia coli bacteria ⚪️ The bacteria lives on sugar, I.e. glucose and lactose Lac operon=3 genes next to each other Code for 3 repressible, inducible enzymes LacZ=codes for Beta-galactosidase (breaks down lactose into galactose and glucose) LacY=codes for permease (increases lactose uptake) LacA=codes for transacetylase

Answer 42

Parental type are offspring that show the same combinations of characteristics as their parents. Recombinant are offspring that show different combinations of characteristics from their parents. The more recombinance you get in the offspring the more crossing over has taken place and the further apart the jeans are in the chromosome.

Answer 43

*Regulatory gene, LacI that codes for repressor is close by *Repressor is a constitutive protein: produced all the time *Repressor protein is an allosteric protein= has 2 binding sites 1. DNA-binding site (to bind to operator region) 2. Lactose-binding site *When lactose binds to its site, the shape of the protein changes *DNA binding site is closed *Repressor is inactivated

Answer 44

When there is no lactose: *Regulatory gene codes for a protein called a repressor *Repressor not bound to lactose *Repressor binds to the operator region close to the gene that codes for B-galactosidase *Because the repressor is bound to the operator, RNA polymerase cannot bind to DNA at the promoter region. *No transcription of the 3 structural genes *Genes are switched off

Answer 45

When lactose is present: * lactose is taken up by bacterium * Lactose acts as an inducer and binds to repressor protein * Repressor changes shape, and cannot bind to the operator region on DNA *RNA polymerase cannot move bind to promoter and move to operator and genes *Transcription occurs *genes are switched on

Answer 46

Benefits of this mechanism: *Allow bacteria to produce 3 enzymes only when lactose is available *When both glucose and lactose are available, bacteria prefers glucose-can repress the lac operon using another transcription factors *3 enzymes produced in equal amounts *Avoids waste of energy and materials

Answer 47

*Genome is larger than prokaryotes *have more more different transcription factors and mechanisms to regulate gene expression *In humans, 10% genes code for transcription factors

Answer 48

*General TFs=form part of the protein complex that binds to the promoter region with RNA polymerase cannot move ➡️ transcription * activate appropriate gene in sequence ➡️ allow correct pattern of development of body regions *determination of sex in mammals *allow responses to environmental stimuli e.g. temp *Products of proto-oncogenes and tumour suppressor genes and other Tags, regulate the cell cycle, growth and apoptosis. *TFs carry out responses to hormones

Answer 49

Without GA: *Transcription factors (i.e. PIF) attached to DELLA protein *TF cannot bind to DNA When GA binds to receptor: *Causes DELLA protein destruction *TF binds to DNA *TF recruits RNA polymerase to bind to DNA *Growth genes switched on/transcribed ➡️production of amylase

Answer 50

A gene codes for a protein which determines the phenotype