Mendelian Genetics Flashcards
What is Mendel’s first law?
The Law of Segregation: “Two members of a gene pair aggregate into separate gametes; half carrying one member of the pair and the other half the other member”
Define the term Pedigree
The recorded ancestry or lineage of a person or family. They show the inheritance of genetic traits
What pattern of inheritances does the disease Brachydactyly depict?
It shows a dominant pattern of inheritance
What are the symptoms of Brachydactyly?
Shortened fingers and toes due to bone malformation
What pattern of inheritance is shown by Huntingtons and how was this discovered?
Dominant inheritance.
- Discovered by Nancy Wexler in a 20 yr study in Maracaibo, Venezuela (incidence is high).
- Allele was found on chromosome 4 leading to development of diagnosis test
Name a disease that shows recessive pattern of inheritance
Cystic Fibrosis
What is meant by the term Genetic Counselling?
The giving of advice to prospective parents regarding the risks of genetic disorders in the future child
What is the equation to calculate the probability of a monohybrid cross?
P (k out of n) = n!/k!(n-k)!×p^k x q^(n-k)
What do the terms n, p, k and q refer to in the formula for the probability of a monohybrid cross?
n = number of offspring p = probability of phenotype under question k = number of times outcome p has occured q = probability of the alternative phenotype (1-p)
What is Mendel’s Second Law?
The Law of Independent Assortment: “during the formation of gametes, the segregation of alleles at one locus is independent of that of the segregation of alleles at any other.
Define the term Dihybrid cross
The inheritance of characters in pairs, i.e. two sets of alleles at a time
What was the ratio of SW:SG:WY:WG of the F2 generation in Mendel’s dihybrid cross using the pea plant
SW:SG:WY:WG
9 : 3 : 3 : 1
Define the term Recombinant
A recombinant is a new mixture of characteristics in an offspring that didn’t exist in the parents
If the number of Heterozygous loci is ‘n’ what is the number of possible types of sperm and egg
2^n
If the number of Heterozygous loci is ‘n’ what is the number of possible types of F2 genotypes?
3^n
Give an Agricultural example of the benefits of recombination.
The dwarf rice of China and India crossed with short stem low yield and tall stem high yield plant –> short stem high yield plant.
Define the term Heterosis
The tendency of a cross-bred individual to show qualities superior to both parents.
What is another term for Heterosis?
Hybrid vigour.
What causes the symptoms of cystic fibrosis?
The failure of a transport protein that moves liquid across cell membranes which causes the lungs to get clogged up with mucus.
Name the 8 genetic aspects that limit Mendelian genetics
Incomplete Dominance, Codominance, Multiple Alleles
Lethal Alleles, Pleiotropy, Gene Interaction, Epistasis and Complementation
Define Incomplete Dominance and give an example.
A heterozygote intermediate between the dominant homozygotes. TAY SACHS carriers- have intermediate levels of the HEXOSAMINIDASE A enzyme.
Define Co-dominance and give and example
Both phenotypes are seen rather than an average of the two, An example is the ABO blood group system. An AB genotype will make both A and B antigens.
Give another example of Co-dominance
Carriers of Sickle cell Anaemia carry both the mutated and normal forms of Haemoglobin
Define Multiple Alleles and give an example
An allele of a genetic locus having m ore than two allelic forms within a population. An example is the ABO blood type locus.
Define the term Lethal Alleles and give an example.
Alleles that cause an organism to die only in the homozygous form. Achondroplasia (dwarfism) is lethal in the homozygous.
What is the cause of the symptoms of Achondroplasia?
A mutation in the fibroblast growth factor receptor 3 gene (FGFR3)
Define the term Pleiotropy.
The principle that one gene with visible effects influences many characteristics simultaneously
Explain why all blue eyed cats are deaf.
Pleiotropic effect. These cats lack melanin causing blue eyes and melanin also used in inner ear process of sound.
Give an example of Pleiotropy.
Sickle cell haemoglobin caused by point mutation (glu subbed for val); has effects on kidney, heart and brain.
Define Gene Interaction
Several Genes affecting one characteristic.
Give an example of Gene Interaction
Sex Limitation - the expression of a particular characteristic limited to one gender. Sex limited genes often respond to sex hormones of a particular sex.
Give an example of Sex limitation
Pattern Baldness- hets male go bald due to production of testosterone but hets female no baldness due to lack of testosterone.
Define Epistasis. How is this an example of Gene Interaction?
The suppression of the effect of one gene by another.
Give an example of Epistasis.
Male pattern baldness- this gene is epistatic toward the gene for hair colour.
Give an example of Epistasis
Albinism- the gene for albinism is epistatic towards the genes for skin pigmentation.
What is the Secretor Phenotype an example of?
Gene interaction. Secretor Phenotype involves the interaction between ABO locus and Se locus. Homo or het Se will produce ABO substances in saliva/sperm.
Define Complementation.
When two strains of an organism with different homo recessive mutations produce the same mutant phenotype or wildtype when mated.
Give an example of Complementation in plants
The white and purple foxglove- WT is purple. When white plants from diff populations crossed, the WT purple is F1.
Give an example of Complementation of in humans.
Deafness- many different loci affect hearing due to different components involved in sound. Offspring of two deaf people often leads to WT normal hearing.
Give an example of Incomplete Dominance in plants.
Mirabilis Japonica- 4 o’ clock plant can be RR (red) or WW (white). Red crossed with white plants produces RW which are pink.
