bio inheritence

diploid

• have 2 copies of every chromosome (one maternal, one paternal) with the exception of the sex chromosomes, these pairs are all homologous)

haploid

•  have 1 copy of every chromosome, produced from diploid germ cells via meiosis

zygote

• Fusion of 2 haploid gametes (sperm + egg) via fertilsation will result in the formation of a zygote that can grow into a new organism via mitosis

• If chromosome number was not halved in gametes, then the number of chromosomes would double in every generation (polyploidy)

genotype

• Sexually reproducing organisms inherit their DNA sequences from both parents - they will have 2 copies of every type of chromosome (one paternal, oe maternal)

• While homologous chromosomes share the same genes, but because they came from different sources (maternal vs paternal origin) their base sequences may differ 

  • Alternate forms of a gene are called alleles, diploid cells will posses 2 alleles for each gene

• The allele combination for any given gene is referred to as the genotype and can be characterized as 

  • Homozygous - when the alleles are the same

  • Heterozygous - when the alleles are different 

phenotype

• Observable characteristics of an organism - physical characteristics (curly hair, hair color, eye color) and structural (abilitiy to distinguish between diff colors) characteristics

• Determined by gene makeup of environmental factors

  • Genotype only: blood type, ey color, genetic conditions like haemophilia

  • Enviroenmental only: learned behaviors, cellular traumas, infectious diseases

  • Both: skin coloration, height, weight, metabolic conditions

phenotypic plasticity

• Capacity for an organism to alter their features in response to environmental triggers by varying patterns of gene expression

• Ex. freshwater snails 

  • Snails with smaller and more round shells are more crush resistant and better protected from predation

  • Freshwater snails may alter their shell structure in the presence of predator fish by changing the expression patterns of biomineralization

• Ex. production of melanin when exposed to sunlight to protect the skin from UV damage

  • Change in gene expression results in increased production of melanin in the skin 

genetic crosses

• Principles of inheritance demonstrated by undertaking breeding experiments in flowering plants

• Pollen is transferred from the anthers of one plant to stigma of other

• When gametes fuse, they form a zygote that develops into an embryo inside a seed

• The parents are known as the P generation and the offspring are the F1 generation

• F2 generation are offspring of F 1

dominance

• Many traitrs follow a classic dominant/recessive pattern of inheritance whereby one allele (dominant) is expressed over the other (recessive)

• Genes code for a polypeptide and recessive alleles of genes are produced by mutation from dominant alleles 

• Homozygous dominant and heterozygous forms are phenotypically indistinguishable and the recessive allele is only expressed in a  homozygous state 

Phenylketronuria

• Disease due to re cessive allele

• Allele is produced by mutation of the gene coding for the enzyme phenylalanine hydroxilase

• Enzyme converts phenylalanine into tyrosine

• A person with 2 recessive alleles of PKU gene cannot produce the functioning enzyme which causes phenylalanine to accumulate in the body and tyrosine deficiency will develop

• Consequence: intellectual disability and mental disordrs

gene

• Length of DNA with a base sequence that cn be hundreds or thousands of bases long

• Different alleles of a gene differ from each other by one or few bases

• Positions in a gene where different bases can be present are called single nucleotide polymorphism

multiple alleles

• There can be many different alleles for the same gene

• A gene pool is all the genes of an individual in a population

• Each individual receives a maximum of 2 alleles form the gene pool

• Presence of multiple alleles creates complexity in inheritence patterns that extend beyond a binary dominant/recessive paradigm

  • Some traits exhibit a dominance hierarchy in their phenotypes

  • Others may demonstrate a blended or combined phenotype

codominance

• Codominance occurs when pairs of alleles are both expressed equally in the phenotype of a heterozygous individual

codominance: ABO blood group

• The ABO blood group system in humans is an example of multiple Alleles

Phenotype	Genotype
Blood Type A	IAIA  or IAi
Blood type B	IBIB or IBi
Blood type AB	IAIB
Blood type O	ii

• There are 6 possible genotype sbut only 4 phenotyoes

• O allele is recessive

• Genotype AB is an example of codominance

• reasons for 2 blood groups to be codominant:

  • All three alleles cause the production of a glycoprotein in the membrane of red blood cells

incomplete dominance

• While comdominance occurs when 2 characterustics are both expressed autonomously in the phenotype, incomplete dominance occurs when the characteristics blend together

  • Eg mirabilis Jalapa when plants with dark pink flowers (C^PC^P) are crossed with white flowered plants (C^WC^W), the offspring will have light pink flowers ((C^PC^W)

sex linkage

• In humans, sex determination involves a pair of chromosomes calle dthe X and Y chromosomes

• Female psess xx chromosomes while males posses xy

• The y chromosomes contain the genes responsible for developing male sex characterustics - in it's absence, the female sex organs will develop ovaries

• Hence the male gamete will dteermine the sex of offspring - as the female egg will always contain an x chromosome

sex chromosome abnormalities

• XXY - boy with klinefelters syndrome

• X - girl with turner’s syndrome

sex of individual

• Male : the y chromosome contains a key gene called the SRY gene known as the TDF responsible for the development of testies in male embryo

• Female - no Y chromosome → No TDF → development of ovaries

sex linked inheritance

• inheritance pattern when a gene controlling a characteristic is located on a sex chromosome

• Because males and females have diffrent sex chromosome combinations, the patterns of inheritence will differ according to sex

• Sex linked alleles are rperesnted as superscripts attached to the relevant sex chromosme ( X^A  or  X^B)

• Because the y chromosme contains very few genes, the majority of sex linked traits are x- linked

hemophilia

• Genetic disorder wherby the body’s ability to control blood clotting is impaired

• The formation of a blood clot is controlled by a cascade of coagulation factors whose genes are located on the X chromosome

  • When one of these factors becomes deffective, the clotting cascade becomes ineffective - bleeding continues for a long time

• This is an exmaple of a x-linked recessive condition, meaning it occurs more frequently in males

pedigree charts

• Chart of genetic history of family over several generations

autosomal inheritance

• Autosomal dominant

  • If both parents are affected and an offspring is unaffected, the trait must be dominant (parents are both heterozygous)

  • If both parents are unaffected, all offspring must be unaffected (homozygous recessive)

• Autosomal recessive

  • If both parents are unaffected and an aoffspring is affected, the trait must be recessive (parents are heterozygous)

  • If both parents show a trait, all offspring must also exhibit the trait (homozygous recessive)

x - linked inheritance

• Genetic disorders caused by mutations to

  • X linked dominant

    • If a male shows a trait, shown by all daughter cells as well as his mother

    • An unaffected mother cannot have affected sons or affected father

    • More common in females

  •  X linked recessive

    • If a female shows a trait, shown by all sons as well as fatyehr

    • An unaffected mother can have affected sons if she is a carrier (heterozygous)

    • X - linked recessive traits tend to be more common in males

polygenetic traits

• Variation in phenotypes for a particular characteristic can either be continuous or discrete

• Phenotypic characteristics are not soley determined by genotype, but also influenced by environmental factors 

• For example, skin color is controlled by multiple melanin producing genes and also affected by factors such as sun exposure 

continous

• the trait is influenced by multiple genes (polygenetic), environmental factors may influence the trait, ex: tree height, body mass of animals, skin color, human wrist circumference

discrete

• the trait is influenced by one or a few genes, enviornmental factors do not usually influence the trait, ex: ABO blood groups, number of egges laid by birds, left or right handed dnail shells, smooth wrinke peas

box and whisker plot

• Statistical tool that can be used to represent data for a continuous variable such as heigh

• Plot shows minimum, maximum, medial values, and demonstrates the range via a lower and upper quartile

• Allows researches to easily asses how variable the data is and whether or not it is skewed in a particular direction

• Allows for statistical dtermination of outliers 

• For a box-and-whisker plot, a data point is categorized as an outlier if it is either above the third quartile or below the first quartile by a value of more than 1.5 time the interquartile range (IQR) 

gene assortment

• Independent assortment is the segregation of the alleles of two genes so that the outcome with each gene has no effect on the outcome with the other 

• The combinations of alleles that remain together are therefore random

• The movement of the chromosomes to diffrent poles is random and the consequence is that every allele has 50% chance of being pulled too either pole

• The alleles of a gene therefore segregate independently from the alleles if another gene 

dihybrid cross

• Step 1: Designate characters to represent the alleles (capital for dominant, lower case for recessive)

• Step 2: write down the genotype and phenotype for the parents (P generation)

  • Always pair alleles from the same gene and always write capitals first (eg AaBb)

• Step 3: write down all the potention gamete combinations for both parents

  • Foil method

• Step 4: use a punett sequare to work out potential genotypes of offspring

• Step 5: write out the phenotype rations of potential offspring

gene linkage

• 20,000 genes in genome that code for polypeptide, each gene has a base sequence and a locus

• Locus: specific position of a gene on one of the chromosomes

• Genes that are located close to each other on the same chromosome do not assort independently and instead show linkage 

  • Most linkages occur on autosomes (can be linked on X)

• Gene linkage is indicated if the F2 ratio differs significantly from the expected ratio for unliked genes (9:3:1)

• Likged genes will be inherited together

• Linkes genes are represented as vertical pairs (AB//ab)

recombinants

• Individual with diffrent combination of alleles/traits from either parents 

• Occur as a result of gene recombination which happens during meiosis

• Random orientation of bivalents results in new combinations (unlinked genes). 

• Crossing over produced new combinations (for linked genes)

• Frrquency of recombination between 2 genes can be measured by crossing individuals that are heterozygous for both genes to individuals that are homozygous recessive for both genes 

chisquared test

• Statistical measure that are used to determine whether the diffrence between a observed and expected frequency distribution is statistically significant

•  Step 1: Identity hypothesis (null versus alternative)

  • Null: There is no significant diffrence between observed and expected frequencies

  • Alternative: There is a significant difference between observed and expected frequences

• Step 2: Construct a table of frequences (observed versus expected)

• Step 3: Apply the chi-squared formula

• Step 4: Determine the degree of freedom (df)

  • = n - 1 (n is number of classes)

• Step 5: Identify the p-value (should be <0.05)