Basic Mendelian Genetics Flashcards
What is the ratio for a monohybrid cross?
3:1
Explain Mendel’s law of segregation
One copy of each gene per parent is passed on to the progeny
Explained by gamete formation and fertilisation
The two alleles of each gene segregated during meiosis
Then, randomly, one allele from each parent will be present in the zygote
What is the ratio for a dihybrid cross?
9:3:3:!
Explain how Mendel came up the idea of independent assortment
Mendel performed dihybrid crosses. He discovered that the combinations of traits in the offspring of his crosses did not always match the combinations of traits in the parental organisms. From this data, he formulated the Principle of Independent Assortment.
Inheritance of one trait has no effect on the inheritance of another trait
New phenotypic combinations: recombinants: shuffling of alleles of different genes
Explain what co-dominance is
The alleles in an F1 hybrid phenotype showing both of the parental traits are termed co-dominant
The offspring are essentially a mosaic of the parents
Define Allele
A variant from a gene; we inherit two alleles for each gene; alleles the same (homozygous); alleles different (heterozygous)
Define Polymorphism
Natural Variation within a gene; no adverse effects on the individual and occur with fairly high frequency in the general population ( greater than 1%)
How many alleles are there in the ABO blood group?
3
Which of the blood group alleles are dominant and which ones are recessive
O = Recessive
A and B = Dominant
Why do alleles A and B show co-dominance?
For an individual who is heterozygous for these two alleles, the phenotype of both alleles is completely expressed, thus providing blood type AB
Define Pleitrophy and give an example
A single gene may affect a phenotype in many ways
The allele for sickle-cell disease is an example
Explain what happens in sickle cell anemia
Autosomal recessive
Functional impairment of hemoglobin beta chain; oxygen-carrying capacity of RBCs is affected
Explain what haploinsufficiency is
Some phenotypes can be sensitive to the amount of functional protein produced
Heterozygote for a loss-of-function mutation that generates less than the normal amount of functional gene products may look completely different from the wild-type organism
Geneticists use the term haploinsufficiency to describe rare situations in which one wild-type allele does not provide enough of a gene product to avoid a mutant phenotype
Around 800 haploinsufficient genes in humans
True or False genes come in alternative forms called alleles
True
True or False: Two same alleles are called heterozygosity
False
What is the progeny of a monohybrid cross between 2 heterozygotes?
3:1
Sickle cell anemia: which of the following is correct?
A. Abnormal hemoglobin
B. Sickle-shaped red cells
C. Anaemia
D. Blocked circulation
E. Increased infection to malaria
E
How can you recognize a dominant trait? Which is not correct?
A. Affected Children always have at least one affected parent
B. Two affected parents can produce unaffected children if both are heterozygotes
C. Traits always shown in males
C
A genetic cross using a homozygous recessive will give a phenotype of? WHta crossed to a heterozygote?
1:1
What type of children are not possible from two AB parents?
O
The child is group O, mother group A., what should the father NOT be?
AB
Explain what autosomal recessive is
Homozygotes are affected; heterozygotes are carriers.
Affected children can be the children of two unaffected carriers, particularly as a result of consanguineous matings.
All the children of two affected parents should be affected.
Rare recessive traits show a HORIZONTAL pattern of inheritance: the trait first appears among several members of one generation and is not seen in the earlier generations.
Recessive traits may show a VERTICAL pattern of inheritance if the trait is extremely common in the population.
Give 3 examples of autosomal recessive
PKU
Cystic Fibrosis
Sickel Cell Anaemia
Explain Autosomal Dominant
Heterozygotes and homozygous are affected.
Affected children always have at least one affected parent; at least one parent affected.
Dominant traits show a VERTICAL pattern of inheritance; the trait shows up in every generation.
Two affected parents can produce unaffected children, if both are heterozygotes.
Unaffected individuals do not produce affected children.
Give an example of autosomal dominant
Huntington’s Disease
Explain what X-linked recessive is
The trait appears in more males than females.
The mutation will NEVER pass from the father to the son; no offspring of an affected male are affected.
An affected male passes the X-linked mutation to all his daughters, who are thus carriers. One-half of the sons of these carrier females will inherit the defective allele and thus the trait.
The trait often skips a generation as the mutation passes from grandfather through a carrier daughter to grandson.
The trait can appear in successive generations when a sister of an affected male is a carrier. If she is, one-half of her sons will be affected.
There is always an unaffected female in the intermediate generation.
With the rare affected (homozygous) female, all her sons will be affected and all her daughters will be carriers.
Give an example of x-linked recessive
Haemophilia
Explain what x-linked dominant is
More females than males show the aberrant trait.
Trait seen in every generation because it is dominant.
All the daughters but none of the sons of an affected male will be affected (X-linked dominant vs autosomal dominant).
One-half of the sons and one-half of the daughters (despite the sex) of an affected female will be affected.
Give an example of x-linked dominant
Hypophosphataemic rickets - (Vitamin D-independent)
