Biology Mendelian Inheritance Patterns Flashcards

Mendel's Law of Segregation states that during the formation of gametes, the two alleles for a heritable character:

Answer: separate from each other, so that each gamete ends up with only one allele.

Mendel's Law of Segregation explains that for any given trait, the pair of alleles from each parent separate and only one allele is passed from each parent to an offspring. This ensures that each gamete (sperm or egg) carries only one allele for each gene.

In a dihybrid cross between two heterozygous individuals (e.g., RrYy x RrYy), what is the expected phenotypic ratio of the offspring, assuming complete dominance and independent assortment?

Answer: 9:3:3:1

A dihybrid cross involving two traits where both parents are heterozygous results in a characteristic 9:3:3:1 phenotypic ratio. This ratio represents the four possible combinations of the two different phenotypes: 9/16 will show both dominant traits, 3/16 will show the first dominant and second recessive trait, 3/16 will show the first recessive and second dominant trait, and 1/16 will show both recessive traits.

A cross between a red-flowered snapdragon (RR) and a white-flowered snapdragon (WW) produces all pink-flowered offspring (RW). This pattern of inheritance is known as:

Answer: Incomplete dominance

This scenario is a classic example of incomplete dominance, where the heterozygous phenotype is an intermediate blend of the two homozygous phenotypes. Neither the red nor the white allele is completely dominant, resulting in a pink appearance.

Which of the following is a key characteristic of an autosomal recessive inheritance pattern?

Answer: The trait can skip generations, and affected offspring can have unaffected parents.

In autosomal recessive inheritance, an individual must inherit two copies of the recessive allele to express the trait. Unaffected parents can both be heterozygous carriers and pass the recessive allele to their offspring, causing the trait to 'skip' a generation. The trait affects males and females with equal probability.

In humans, red-green color blindness is an X-linked recessive trait. If a colorblind man marries a woman who is a carrier for the trait, what is the probability that their son will be colorblind?

Answer: 50%

A son inherits his X chromosome from his mother and his Y chromosome from his father. Since the mother is a carrier (heterozygous), she has one X chromosome with the normal allele and one with the colorblind allele. Therefore, there is a 50% chance she will pass the X chromosome with the colorblind allele to her son, making him colorblind.

When both alleles for a trait are fully and separately expressed in a heterozygous individual, such as in the AB blood type in humans, this is an example of:

Answer: Codominance

Codominance occurs when both alleles in a heterozygous pair are fully expressed, resulting in offspring with a phenotype that is neither dominant nor recessive, but shows both traits simultaneously. The AB blood type is a prime example, where both A and B antigens are present on the surface of red blood cells.