genetics Flashcards
what is genetics
Examines how DNA sequences in chromosomes (genes) result in different traits (phenotypes)
Studies how genes & traits are passed on from one generation to another
i.e. the study of heredity
what did gregor mendel do?
performed genetic crosses in peas and observed they have specific traits in specific pattern (either or)
either purple or white
wrinkled or smooth
what is a cross
it is mating, pairing specific parents with specific traits to produce off spring
what is a pure breeding plant (pure strain)
plant wheree all their ancestors showed the same traits 100% of the time.
define phenotype
observable characteristics based on genotype
define genotypee
set of genes in a organism (responsible for its traits)
what are true breeding parents called
the P generation
what are the offspring of those parents called
f1 generation (filial or child)
what are the offspring of f1 and f1 called?
F2 generation
what is it called when you cross two different true breeding varieties
hybridization
menders experiment purple vs white flowers:explain
mendel cross bred pure breeding purple and white flowers
used pollen from white to fertilize purple eggs
result : all f1 hybrids have purple flowers
same result when pollen from purple and eggs from white was used
what is the result of menders experiment
all offspring f1 have purple flowers regardless of having one white and one purple parent
what is the law of segregation
Each gamete only carries 1 copy (allele) of each gene (since only have 1 copy of each chromosome)
Lets call our flower colour gene ‘A’ for simplicity
Fuse 2 haploid gametes to form 1 diploid zygote
Each zygote (each F1 plant) will have 2 copies of each gene – 1 from each parent
Each F1 plant will have 1 purple allele & 1 white allele
define allele
different versions of the same gene
explain why all f1 offspring of purple and white flowers were purple
because purple (A) is dominant over white (a) therefore wherever purple shows up it will mask white consequently white is recessive: will not show up alongside purple
explain second part of mendels experiment
cross breeds f1xf1
offspring shows both purple and white in a 3;1 RATIO\
what is the locus of an allele
the location of the gene
what is homozygous
Both alleles at a locus are the same
e.g. AA or aa
what is heterozygous
The 2 alleles at a locus are different
e.g. Aa
what are menders 4 concepts
Different alleles account for variations in inherited characters
For each character an organism inherits 2 alleles; 1 from each parent
if the 2 alleles at a locus differ, the dominant allele determines the organism’s appearance
The recessive allele has no noticeable effect on the organism’s appearance
Law of segregation
2 alleles for a heritable character separate (segregate) during gamete formation & end up in different gametes
what is you are testing more than one gene?
dihybrid crosses
how do you do dihybrid?
FOIL TRAITS
WHAT are the two assortment hypotheses
Independent assortment
Genes (& corresponding characteristics) associate separately
In a gamete, receiving a certain allele for a gene does not influence which allele is received for a different gene*
Dependent assortment
Genes (& corresponding characteristics) associate together
what phenotypic ration does independent assortment result in
9:3:3:1
multiplication rule?
Probability of 2 or more independent events occurring together is calculated by multiplying the probability of each event.
Key word: “And”
addition rule?
Probability of 2 or more mutually exclusive events is calculated by adding their probabilities.
Key words: “Either” “Or”
what are the 5 inheritance patterns
autosomal recessive autosomal dominant x linked recessive x linked dominant y linked
explain autosomal recessive
equal freq in sexes, skips generations, affected offspring born to unaffected parents
explain autosomal dominant
equal freq in sexes, both sexes transmit to offspring, does not skip gens, unaffected parents do not transmit
x linked recessive
males>females affected
affected sons born to unaffected mothers,
never passes from father to son
x linked dominant
females > malees
does not skip gens
y linked
only males affected
passed from father to son
does not skip gens
what gender are sex linked genes more phenotypically expressed?
males
females and their x chromos
inherit two x chromosomes therefore would need two copies of the recessive allele to show recessive phenotype
males and their xy chromos
nothing can mask the recessive x linked gene
examples of sex linked x traits
eye colour
colour blindness
haemophilia
what are the three types of dominance
complete dominance
incomplete dominance
co-dominance
explain complete domincance
phenotypes of heterosexuals zygote and dominant homo are identical
explain incomplete dominance
2 difference alleles for 1 gene are BOTH expressed (intermediate) not an exact blend
something shows through for both
explain co-dominance
2 different alleles for 1 gene are BOTH FULLY expressed
define epistasis
A gene at one locus alters the phenotypic expression of a gene at a different locus
define pleotropy
A single mutation that has multiple effects (produces multiple phenotypes)
define neomorphy
A mutation causes altered function - either expression at a different place or time, or a novel (new) function\
define multifactorial
a trait is influenced by multiple phenotypes and environmental factors
define polygenic
a trait is influenced by multiple genes
what is the epistatic gene
thee gene that is responsible for masking/supressing
THINK DOG EEXAMPLE THERE IS A PATHWAY HAS TO GO THROUGH EPISTATIC GENE FIRST
explain pleiotropy
1 gene is associated with many traits because genes are often active in many plaecees
eex: sickle cell anemia and albinism
give an example of multifactorial traits
height and heart disease/cancer
explain polygenic traits
you will see an additive affect off different alleles/genes
either you will have an additive or no
penetrance and expressivity
Penetrance
Proportion of individuals of a certain mutant genotype that exhibit the mutant phenotype
Quantitative
Depends on modifiers, epistasis, & environment
Expressivity
Severity of the mutant phenotype generated by a particular allele
Qualitative
Depends on genetic background & environment
explain x inactivation
Females condense & (almost completely) de-activate 1 of their 2 X-chromosomes during early embryonic development
Barr-body = condensed X chromosome
Normal females will have 1 barr-body & 1 uncondensed X chromosome per cell
Normal males will not have barr-bodies
what is lyon hypothesis
Females are mosaics
Which X chromosome becomes a barr-body is initially random
Humans: occurs at about day 10
Daughter cells will inherit the same pattern of inactivation expressed by the original cell
