Genetics Final Exam

reciprocal crosses

flip the sexes of the parents

particulate factors

determine phenotype

true or false: genetic traits can skip generations

true

Mendel’s 3 Postulates

1) particulate factors (alleles) exist in pairs

2) one allele is dominant, the other is recessive

3) alleles segregate independently during gamete formation

4) independent assortment (traits assort independently during gamete formation)

metaphase 1

things line up randomly leading to independent assortment

fail to reject

dominant autosomal traits

• no generation skipping

• both genders affected equally

• both genders can pass on trait

• ex. achondoplasia

recessive autosomal traits

• can skip generations

• both genders affected equally

• ex: albinism

autosomal

genes/traits located on any numbered chromosomes (1-22) not sex (X or Y)

complete dominance

one allele is dominant to another

complete recessiveness

recessive allele is phenotypically only expressed when it is homozygous

codominance

two alleles at a locus produce different and detectable gene products in heterozygote

blood type AB is the universal…

acceptor

blood type O is the universal…

donor

ABO blood group gene encodes…

glycotransferases

H antigen encoded by dominant H allele

Bombay blood type (can’t accept other blood types, not even O b/c lack of H substance)

if a girl has blood type O, what are all possible genotypes of her parents?

• AO + OO

• BO + OO

• OO + OO

• AO + BO

• AO + AO

• BO + BO

incomplete dominance

one allele is not completely dominant to another allele of the same gene

the phenotype of heterozygote lies between…

either homozygote

codominance

results from both alleles (both alleles can be expressed, but only one observed)

incomplete dominance

only one allele product gets expressed

gene sufficiency

how many copies of a gene are required to give a normal phenotype

haplosufficent

only one gene copy is sufficient to give a normal phenotype

essential genes

genes that, when mutated, can results in a lethal phenotype (required for survival)

lethal allele

allele that results in the death of an organism

Tay-Sachs disease

• lack of enzyme that breaks down lipids in lysosomes

• results in excess lipids in CNS

huntington disease

huntington protein has too many glutamine amino acids leading to progressive degeneration of brain cells (onset between 30-40 years of age)

epistasis

genetic interaction where one gene pair masks the phenotype of another gene pair

epistatic

masking gee

hypostatic

masked gene

dihybrid crosses (4 phenotypes, 9 genotypes)

recessive epistasis

dominant epistasis

epistasis summary

modifier gene

alters the phenotype of another allelic gene

enhancers

intensify phenotype controlled by the other gene

reducers

decrease phenotypic expression of the other gene

suppressor gene

when modifier gene shifts phenotype associated with a mutant allele toward that of the wild-type

complementation test (also known as cis-trans test)

determines whether two independently isolated mutants have mutations in the same or different genes

complementation test example 1

complementation test example 2

pleiotropy

when a gene influences many traits rather than just one

polygenic traits

• where many genes contribute to producing a phenotype

• usually multifactorial

• influenced by genetics and environment

• many show continuous variation

• meristic traits described by whole numbers

• threshold traits: small numbers of phenotypes

• YOU EITHER ARE ____ OR ARE NOT ____

polygenic traits

• grain colour in wheat

• may be b/c of additive alleles

• may show normal distribution within population

• can estimate number of genes involved (n)

penetrance (on/off)

the phenotype of individuals with a given genotype that exhibits the associated phenotype

expressivity (dim/bright)

degree to which a penetrant gene of genotype is phenotypically expressed

factors that can alter the phenotype of a specific phenotype

• age

• sex

• temperature

• chemicals/nutrition

• epigenetic modifications

phenotypic expression depends upon…

the parental origin of the chromosome carrying the particular allele

maternal/paternal imprinting

turning off the gene from mom/dad (respectively)

position effects

a change in the phenotypic expression of one or more genes (due to change in position of the genome)

genetic anticipation

when a genetic disease appears earlier with each succeeding generation