110 Gene Linkage

Summary

This video explains the concept of gene linkage, where genes located on the same chromosome tend to be inherited together. Using an example of two genes, A and B, the video contrasts inheritance patterns for linked and unlinked genes. For unlinked genes, the inheritance follows the classic 9:3:3:1 ratio seen in Mendel's dihybrid crosses. However, when genes are linked, they exhibit a 3:1 ratio, resembling a monohybrid cross. The video provides a clear understanding of how chromosome structure affects inheritance, emphasizing the impact of gene linkage on genetic variation.

Takeaways

• 😀 Gene linkage refers to genes located on the same chromosome.
• 😀 A chromosome can contain hundreds of genes, and gene linkage happens when two genes that influence different traits are on the same chromosome.
• 😀 When studying gene linkage, consider two genes like 'A' (aging) and 'B' (another trait), each with dominant (A, B) and recessive (a, b) alleles.
• 😀 For unlinked genes, the inheritance pattern follows Mendel's dihybrid cross, resulting in a 9:3:3:1 ratio of offspring phenotypes.
• 😀 When two genes are unlinked, crossing two heterozygotes results in offspring with various combinations of dominant and recessive traits.
• 😀 If the genes are linked on the same chromosome, inheritance differs, as both alleles on a chromosome are inherited together during meiosis.
• 😀 In linked genes, the possible allele combinations are limited to either both dominant or both recessive alleles in gametes.
• 😀 The Punnett square for linked genes shows three-quarters of offspring will express dominant traits for both genes, and one-quarter will be homozygous recessive for both.
• 😀 The linked gene inheritance pattern resembles a monohybrid cross, with a 3:1 phenotypic ratio for both traits combined.
• 😀 Linkage results in a situation where two traits are inherited together, deviating from the typical dihybrid cross ratios seen with unlinked genes.

Q & A

What is gene linkage?

Gene linkage refers to the situation where two genes are located on the same chromosome, meaning they tend to be inherited together during meiosis.

How does gene inheritance differ when genes are unlinked?

When genes are unlinked, they assort independently during meiosis, following Mendel's classic 9:3:3:1 ratio in a dihybrid cross.

What is the classic inheritance ratio observed when genes are unlinked?

The classic inheritance ratio for unlinked genes is 9:3:3:1, which represents the different combinations of dominant and recessive alleles in the offspring.

What happens when two genes are linked on the same chromosome?

When two genes are linked, they do not assort independently, and their inheritance pattern follows a 3:1 ratio, similar to that of a monohybrid cross.

How does meiosis affect the inheritance of linked genes?

During meiosis, homologous chromosomes segregate, and linked genes are inherited together as they are on the same chromosome, resulting in fewer allele combinations.

What does the Punnett square for linked genes look like?

The Punnett square for linked genes shows that the offspring can only inherit combinations where both alleles are either dominant or recessive, leading to a 3:1 phenotypic ratio.

Why do linked genes show a 3:1 inheritance pattern?

Linked genes show a 3:1 pattern because they are inherited together, either as both dominant or both recessive alleles, which reduces the diversity of possible allele combinations.

How do linked genes resemble Mendel’s monohybrid cross?

Linked genes resemble Mendel's monohybrid cross because they involve a single pair of alleles (from one homologous chromosome) and produce a 3:1 ratio of phenotypes.

What is the significance of gene linkage in genetic inheritance?

Gene linkage is significant because it alters the expected inheritance ratios and limits genetic diversity by reducing the number of possible allele combinations in offspring.

How does gene segregation during meiosis affect linked genes?

Gene segregation during meiosis ensures that linked genes remain together in the same gametes, as they are located on the same chromosome, which affects the inheritance pattern.