GENETICS EXAM 1

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Monohybrid Cross

a cross following ONE TRAIT

ex: (TT x tt) are the alleles, but it is both for plant height. thats the ONE trait they are following.

True Breeding

TTxTT would result in TT off spring in F1 making it true bred and tt x tt would result in tt making it also another true bred line, so mendel wanted to see like oh what if i crossed these two would that give me a mixed medium height plant or not?

ONE P.S. Mendel didn’t know the lettering stuff we use that only now.

P₀

original parent generation

ex: TT x tt

F1

off-spring of P₀ generation, the result in F1 is ALLLL heterozygous Tt off spring

F2

we get this generation when we cross the F1 heterozygous genotypes with itself. ( Tt x Tt )

this would give the ratio of

genotypes: (TT) 1 : (Tt) 2 : (tt) 1
phenotypes of = 3:1 because we have 3 of the off spring showing the dominant tall trait and 1 of the off spring showing the recessive short trait.

genotype

the allele combination

ex: TT, Tt, or tt

phenotype

the observable trait on the outside

ex: Tall or short

Gamete

and EGG or a SPERM carrying one allele for each gene

ex: a Tt parent can make gametes carrying a “T” allele or a “t” allele for the height gene.

Back Cross

Crossing an off-spring back to one of its original parents

ex Tt being an f1 off spring being back crossed to TT or tt which are its original parents.

Test Cross

Crossing an individual with a dominant phenotype and unknown genotype with a homozygous recessive individual to help determine whether the unknown genotype is Tt or TT

ex: a plant shows all tall but we dont for sure know whether it is TT or Tt, so we cross that plant with a tt so see if any of the off spring is short(tt) or all of them are tall. if they are all tall they we can be like okay their genotype is TT, but if even one of the off spring is short then we know that unknow individual had the T”t” allele and was heterozygous.

Observe many many many off-spring to get accurate and reliable results, you cant determine that the genotype of parent was TT if you’re only observing a small group of plants.

Principle of segregation

During gamete(egg or sperm) formation a parent will pass wither T or t to their gamete depending on their genotype so if a parents genotype if TT then they will only pass T, if the parents genotype if tt they will only pass t, if their genotype if Tt, they can pass EITHER T or t.

Homologous Chromosomes

A pair of chromosomes, one inherited from each parent, that have the same genes at the same locations (locus). They can carry different alleles of those genes

Ex: T on one chromosome from either mom or dad. OR a t on the other chromosome, from either mom or dad.

Locus

where the gene sits on a chromosome, like the location of the gene o a chromosome

allele

a version of a gene

gene

a stretch of DNA that helps us determine a trait.

the TRAIT is what we are observing.

conditional probability

You are context clues from what you are given to narrow down your answer to the possible outcomes.

Ex: john has brown eyes, his sister has blue eyes, his parents have brown eyes and his wife has blue eyes. using this given you can do the calculation.

Binomial Probability

You are given a total and you are also given a result you want. Using this information you can find the probability of that getting that result.

Ex: you can think like oh mom and dad want 2 girls and 1 boy, what is the probability of this even happening given that both genders have a 50% chance of being born. you can now do that math with this given and figure it out!

Consanguity

occurs when two related persons mate and have off spring. often a clue that the off spring will be autosomal recessive.

Incomplete Penetrance

When a individual has the diseased allele but they don’t express the trait.

Variable Expressivity

When an individual has the diseased allele but they express the trait different, meaning the severity and features vary person to person who inherits the trait.

Autosomal vs Sex-linked

Autosomal means that the trait is one chromosomes 1-22 and each gender has an equal chance of receiving this trait.

Sex-linked means that the allele is present on the 23rd chromosome and that males and females do not have an equal chance of receiving this trait.

Dominant vs Recessive

A dominant trait is when an UPPER CASE letter is present in an individuals genotype. if its homozygous dominant is crossed with a homozygous recessive we know that the dominant allele will over power the recessive allele and all off spring will be carriers. dominant = strong and expressed more often

A recessive trait usually is only expressed when the genotype is homozygous recessive. the dominant allele usually over powers the recessive allele if it is present in the genotype

so we can understand that in a pedigree if a trait is skipping generations then it is most likely a recessive trait, if it is present in every single generation and at least one parent has it then, it is a dominant trait.

Proband

this was the person who had the trait and went to the geneticist to get tested n stuff.

Genetic Maternal Effect

The mothers genotype is expressed as the child’s phenotype despite the child having a different genotype. so if mom was Bb for brown eyes, and then the child was bb for blue eyes, the child will still express the Bb phenotype which is brown eyes despite having the blue eye genotype.

this is because the mothers genotype affects the proteins placed inside the egg VERY early during development.

Cytoplasmic Imprinting

Usually passed from mother to off spring (could be male or female). During cell division for humans we know that outside the nucleus the cytoplasm holds mitochondrial DNA in animal cells and then chloroplasts in plant cells. when the cell creates gametes, the mitochondrial DNA randomly segregates into those cells, so some might have diseased mutant mitochondrial DNA which creates diversity and also could effect the expression of the phenotypes in the off spring.

its mother to off spring because mother provides most of the cytoplasm early during development.

the trait can vary heavily even among relatives because of the mutant that can be passed on providing diversity.

Reciprocal Cross

switching the gender of the parent who is infected.

EX: if the mother bb (infected) and dad is Bb then we would swtich them so mom=Bb and dad would = bb

if talking about cytoplasmic inheritance then if the mother had the trait but we switched it to dad having it, the ids wont have it since mother is the one who provides most of the cytoplasm during the cel division.

Genomic Imprinting

this is literally a regulating thing. for example both parents will pass on the IGF2 gene which is a growth gene, but ONLY the dads will be expressed(usually only dad is expressed), the mother’s will be silenced. This happens because if both are expressed then there could be an over growth and if there is none expressed then it would be too little growth gene causing a shortness condition. basically genomic imprinting controls which parents genes are being silenced or expressed to regulate and create human.

EPIGENETIC PROCESS