Linkage and Chromosome Mapping

What is linkage in genetics?

• Random assortment of genes on different chromosomes

• Inheritance of two or more genes together on the same chromosome

• Exchange of genetic material between sister chromatids

• Inheritance of traits due to environmental factors

Answer explanation

Linkage in genetics refers to the inheritance of two or more genes together on the same chromosome, meaning they are likely to be passed on together during reproduction, unlike genes on different chromosomes that assort randomly.

What does a recombination frequency of less than 50% indicate?

• Genes are not linked

• Genes are linked

• Genes are assorting independently

• Crossing over does not occur

Answer explanation

A recombination frequency of less than 50% indicates that genes are linked, meaning they are located close to each other on the same chromosome and tend to be inherited together.

What is the unit for genetic map distance?

• Chiasma

• Recombination factor

• Centimorgan (cM)

• Linkage ratio

Answer explanation

The unit for genetic map distance is the centimorgan (cM), which represents a 1% chance of recombination occurring between two genes during meiosis. This makes it the standard measurement in genetics.

What is the relationship between crossing over and genetic variation?

• Crossing over decreases genetic variation

• Crossing over prevents recombination

• Crossing over increases genetic variation by producing new allele combinations

• Crossing over creates new genes

Answer explanation

Crossing over increases genetic variation by producing new allele combinations during meiosis, allowing for greater diversity in offspring. This process reshuffles genetic material, leading to unique combinations of traits.

Which type of linkage results in no recombination?

• Incomplete linkage

• Complete linkage

• Independent assortment

• Triple linkage

Answer explanation

Complete linkage occurs when two genes are located very close to each other on the same chromosome, resulting in no recombination during meiosis. This means the alleles are inherited together without mixing.

In chromosomal mapping, what does a recombination frequency of 1% represent?

• 10 cM

• 1 cM

• 100 base pairs

• 10% recombination

Answer explanation

A recombination frequency of 1% corresponds to 1 centiMorgan (cM) in genetic mapping, indicating that genes are 1 cM apart on a chromosome. Thus, the correct answer is 1 cM.

What is a double crossover?

• Crossing over in non-homologous chromosomes

• Exchange of genetic material at two different loci between chromatids

• Exchange that involves only sister chromatids

• Single chiasma formation

Answer explanation

A double crossover refers to the exchange of genetic material at two different loci between chromatids, resulting in a more complex rearrangement of genetic information compared to a single crossover.

What determines the strength of genetic linkage?

• Number of alleles on a chromosome

• Distance between linked genes

• Type of recombination event

• Size of the chromosome

Answer explanation

The strength of genetic linkage is primarily determined by the distance between linked genes. Genes that are closer together on a chromosome are less likely to be separated by recombination events, thus maintaining their linkage.

Which chromosomal structure is formed during crossing over?

• Centromere

• Chiasma

• Chromatid

• Telomere

Answer explanation

During crossing over, homologous chromosomes exchange genetic material, forming a structure called a chiasma. This is where the chromosomes physically connect and overlap, facilitating genetic recombination.

What is the maximum recombination frequency observed between two genes?

• 100%

• 75%

• 50%

• 25%

Answer explanation

The maximum recombination frequency between two genes is 50%. This indicates that the genes are on the same chromosome but are far enough apart that they assort independently, leading to a maximum of 50% recombination.