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Heterosis and Inbreeding Depression-Part-2: Inbreeding Depression
Prof. S.K. Singh BHU
Overview
This video explains the concept of inbreeding depression, which is the reduction in vigor and fertility due to inbreeding or self-pollination. It details how to measure inbreeding depression using a formula comparing F1 and F2 generation performance, illustrating with a yield example. The video discusses the effects of inbreeding, such as the expression of deleterious recessive alleles and increased homozygosity, contrasting it with heterosis. It then explores the varying degrees of inbreeding depression observed in different crops, categorizing them into high, moderate, low, and lacking inbreeding depression based on their cross-pollination tendencies and genetic makeup. Hypothetical genetic examples are used to clarify these concepts.
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Chapters
- •Inbreeding depression is the loss of vigor and fertility resulting from inbreeding or self-pollination.
- •It is the reverse effect of heterosis.
- •Inbreeding increases homozygosity, leading to the expression of recessive alleles.
- •The formula for measuring inbreeding depression percentage is (F1 bar - F2 bar) / F1 bar * 100.
- •F1 bar represents the average performance of the F1 generation.
- •F2 bar represents the average performance of the F2 generation.
- •This measurement is applicable to F1 hybrids regardless of their pollination system.
- •Inbreeding leads to increased homozygosity.
- •This results in the expression of lethal and sub-lethal alleles.
- •There is a reduction in vigor and fertility.
- •Yield and other desirable traits are negatively impacted.
- •The primary cause is increased homozygosity.
- •This homozygosity allows deleterious recessive alleles to be expressed.
- •These expressed recessive alleles negatively affect plant performance.
- •The degree of inbreeding depression varies based on the crop's natural pollination system.
- •Highly cross-pollinated crops tend to show higher inbreeding depression.
- •Self-pollinated crops generally show little to no inbreeding depression in their natural varieties.
- •Observed in highly cross-pollinated species like alfalfa and carrot.
- •A large proportion of plants produced by selfing may exhibit lethal characters and not survive.
- •Surviving inbreds may have significantly reduced yield (less than 25% of the open-pollinated variety).
- •Characterized by high heterozygosity in the original population.
- •Seen in crops like maize, sorghum, and pearl millet.
- •Lethal and sub-lethal types appear, but a substantial proportion of offspring can be maintained.
- •Inbred lines can be developed, but the best inbred line may yield only up to 50% of the original open-pollinated variety.
- •Represents a moderate level of heterozygosity.
- •Occurs in crops with lower cross-pollination rates than maize or sorghum, such as onion, cucurbits, and sunflower.
- •Only a small proportion of offspring show lethal or sub-lethal traits.
- •Reduction in yield is small or sometimes absent.
- •Some inbreds may perform as well as their open-pollinated counterparts.
- •Characterized by lower levels of heterozygosity compared to moderate cases.
- •Primarily observed in naturally self-pollinated crops.
- •These crops are already highly homozygous in their natural state.
- •Selfing does not lead to a significant increase in homozygosity or expression of deleterious recessives.
- •While they may show heterosis, they do not exhibit inbreeding depression in their natural varieties.
Key Takeaways
- 1Inbreeding depression is the detrimental effect of self-pollination, leading to reduced plant vigor and fertility.
- 2The phenomenon is caused by the increased homozygosity, which exposes harmful recessive alleles.
- 3Inbreeding depression can be quantified by comparing the performance of F1 hybrids to their F2 generations.
- 4The extent of inbreeding depression is strongly influenced by a crop's natural cross-pollination tendency.
- 5Highly cross-pollinated crops experience severe inbreeding depression, often resulting in non-viable offspring.
- 6Moderately cross-pollinated crops show significant but manageable inbreeding depression, allowing for the development of inbred lines.
- 7Crops with low cross-pollination rates exhibit minimal inbreeding depression.
- 8Naturally self-pollinated crops, being already homozygous, generally do not show inbreeding depression in their standard varieties.