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Flashcards in Modifications Of Mendel Deck (14):

Define incomplete dominance and give example

Expression of heterozygote is intermediate between dominant homozygotes

• Four o’clock plant- red white pink
• Mendel’s peas- smooth/wrinkled
• Tay Sachs disease- homozygous recessive, hexoaminidase enzyme activity


Define codominance and give an example

Phenotypic effects are fully and simultaneously expressed in heterozygote

• Red white cow- spotted
• Sickle cell haemoglobin


Define multiple alleles

More than two alleles occurring at a locus

• Drosophila and human eyes
• ABO blood groups


How does the ABO blood group system work? What is involved other than multiple alleles?

A and B each produce different antigens
O produces none
A n-acetyl galactosamine
B galactose
AB produces both

Complete and codominance


Define pleiotropy

One gene affects many characteristics

• All blue eyed white cats are deaf
• Sickle cell haemoglobin is change in one base/amino acid- many detrimental effects- anaemia, heart failure, enlarged spleen


Define gene interaction

Several genes affect one character. Alleles at one locus can alter the phenotype produced by an allele at another locus

• Autism
• Sex limitation effects in males- testosterone> secondary sex characteristics
• BRCA1 mutations- increase in breast cancer due to interaction btw cell division genes and oestrogen
• Mouse coat colours- at least 5 interacting loci


Define epistasis

One allele preventing another at a different loci from expressing its effects


What ratio results from a dihybrid cross involving epistasis?


Eg. Albino mice


Define complementation and give an example

Two strains of an organism with different homozygous recessive mutations that produce the same phenotype

• Foxgloves:
w1w1 W2W2 =white
W1W1 w2w2 =white
cross-> F1 W1w1 W2w2 =purple
F1 cross F1 -> F2 9purple:7white


What are complementation tests?

Show whether two alleles at a locus are involved or two/or more different loci

I.e. Cross two mutant homozygotes from different populations
If same locus, mutant F1 phenotypes shown
If different loci, parental phenotype shown- now het’s at both loci

Eg. Human deafness- many loci- outer ear, cilia of inner ear, nerve connections to brain. Two deaf parents can have hearing child.


What is a test cross?

Dominant individual crossed with homozygous recessive to determine if individual is homozygous or heterozygous


Define atavism

Phenotypic traits disappearing then reappearing later in the phylogenic tree


What is a back cross?

Crossing a hybrid with one of it’s parents/genetically similar individual
-> offspring with genetic identity closer to parents


Define lethal alleles and give an example

Homozygotes for certain alleles can be lethal

• Mice- Y allele dominant for yellow coat (y=wild-type), but recessive for viability-> Yy cross Yy -> 2yellow:1wild as YY dies
• Manx cat= no tail. Homozygous Manx allele= lethal
• Barchydactyly