Session 1: Single Gene Inheritance Flashcards
What are incomplete dominance, co-dominance, and lethal alleles examples of?
When different phenotypic traits are observed in the offspring compared to the predicted ratios, it is an indication that there is an alteration to the patterns of inheritance.
What is incomplete dominance?
When hybrids/heterozygotes have an appearance that is intermediate or blended between the phenotypes of the parents. E.g. red flower and white flower making pink flower.
What is co-dominance?
When the two alleles are both expressed and the offspring has characteristics of both alleles. E.g. a black chicken and a white chicken making a black and white speckled chicken.
What are ABO Blood Groups?
Humans have several different blood grouping systems, based on the presence or absence of different antigens on the surface of red blood cells (erythrocytes).
What are lethal alleles?
Alleles that cause an organism to die only when present in homozygous condition. The gene involved is considered an essential gene, when this essential gene is mutated it can result in a lethal phenotype. Lethal alleles result in a 2:1 phenotype ratio in the surviving offspring.
What decides whether an individual is male or female?
The male parent’s gametes determine the sex of the offspring. This occurs during the production of secondary spermatocytes (meiosis II) - half the receive an X chromosome while half receive a Y chromosome.
What is difference between Y and X chromosomes?
The Y chromosome is a truncated X chromosome (shorter, without the top or end). Because the Y
chromosome is truncated, there are many genes with an allele on the X
chromosome but no corresponding allele on the Y chromosome.
Describe the two variants of X linked genetic conditions.
X linked dominant or X linked recessive. X linked dominant genes only require one copy of the allele for expression, whether in males or females. X linked recessive genes are different for males and females: In males, one allele gives expression In females, two alleles are required for expression.
Describe the inheritance of colour blindness.
The allele for colour blindness can be displayed as
X^c. It is a recessive condition. In carrier females, the normal allele (X) cancels out
the affect of the X^c. In affected males, there is no normal X to cancel out the X^c. If the father is colour blind: daughters are carriers and sons are normal. If the mother is a carrier: 1/2 the daughters are carriers, 1/2 the sons are colour blind.
What are other examples of X linked recessive conditions?
Haemophilia: lack of clotting factor VIII, increased bleeding and bruising.
Gout: Metabolic problem leading to increased amounts of uric acid in the body. This causes joint inflammation & kidney stones.
Describe X-linked Dominant Conditions.
These are much rarer. The frequency is similar in males and females. However, the absence of male-to-male transmission
distinguishes X linked dominant diseases from
autosomal dominant diseases, in which both sexes
are also equally affected. If the father has the
condition, then none of his sons will be affected, but all daughters will be
affected. If the mother has the
condition, then all of her offspring have a 1⁄2 chance of having the condition.
Describe the ABO Blood Groups: type, antibodies, and antigens.
Red blood cell type A has Anti-B antibodies and an A antigen. Red blood cell type B has Anti-A antibodies and a B antigen. Red blood cell type AB has no antibodies and both A and B antigens. Red blood cell type O has both Anti-A and Anti-B and no antigens.
Describe overall male and female sex chromosomes:
Both sexes have 44 autosomes and 2 sex chromosomes (46 in total) and therefore gametes have 22 autosomes and 1 sex chromosome. Males have XY sex chromosomes, females have XX sex chromosomes.
