Examples of Homologous and Analogous Structures

What do you mean by homologous structures? Well, homology represents common ancestry. In other words, when we say homologous structure, it means we are talking about two structures which have a similar origin. However, it is important to mention that though two structures have a similar origin, that does not mean they will have a similar and function as well. For instance, thorn and tendrils of Bougainvillea and Cucurbita. Both are modifications of stem buds, but they perform different functions. For example, a thorn is a structure for protection while tendrils are structures for climbing and support to the substratum.

If we take an example in animals, humans, cheetah, whale, and bat show similar anatomical structure -- all of them possess humerus, radius, ulna, carpals, metacarpals, and phalanges, but they perform different functions.

Besides, homology represents divergent evolution because though their origins are same, but their structure and functions are different.

Now, let's discuss about analogous structures. Well, an analogy is just the opposite of homology meaning, two structures show analogy when they have a different origin, but similar structure and function. For instance, the eye of octopus and mammals; flipper of penguins and dolphins. sweet potato (root modification) and potato (stem modification). 

Octopus belongs to the phylum Mollusca and cat belongs to the phylum Mammalia. However, both possess eyes which have a similar structure and function. Besides, analogous structure leads to convergent evolution because though they have a different origin, but structurally and functionally, they are the same. 

Q. What do you think about vertebrate heart and brains? Do they show homology or analogy?

Ans: Both vertebrate heart and brain show homology. For example, chicken heart and fish heart show homology because they evolved under common ancestry as they show structures like auricle and ventricle. On the other hand, vertebrate brains are divided into forebrain, midbrain, and hindbrain - common subdivisions of the brain in all vertebrate animals. 

Now, I let you think about other homologous and analogous structure.

Heart of Fish and Heart of Crocodile

Wings of butterfly and wings of birds

Thorns of Bougainvillea and spines of Opuntia

Please write your answer in the comment box.

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Introduction to the Complementary Gene Interaction

Complementary gene interaction is an intergenic or interallelic gene interaction in which two dominant genes express themselves to the same character; independently;  however, when they are combined together, they express to a different character. In other words, two dominant genes when combined, complement to each other.

Complementary gene interaction is present in sweet pea (Lathyrus odoratus). There are two varieties of sweet pea plants -- both produce white flowers. However, when two varieties are crossed together, purple flowers are formed. I have described everything about complementary gene interaction in the video below:

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Concept of Intergenic and Intragenic Gene Interaction

There are mainly two types of gene interactions namely intragenic and intergenic gene interaction. First, we will discuss the intergenic gene interaction. It is an interaction between two different genes located on either the same chromosome or different chromosome. To understand this concept, I have discussed it in detail on my video below: 

In the case of intragenic gene interaction, it is an interaction between two alleles of a gene present on the homologous chromosome. Please watch the video until the end to understand the concept in a very easy way.

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Why are night blooming flowers generally white?

White is considered as the lightest color and achromatic without any hue as it fully reflects and scatters all the visible spectrum of light. White stands out dramatically with limited light. Besides, color, smell and overall form of any flower are produced for the sole purpose of pollination. During the daytime, flowers with colored petals generally attract butterflies, bees, and other insects. On the other hand, night-blooming flowers usually attract moths and other nocturnal pollinators. Night blooming flowers are generally white and fragrant as well because there is no purpose for them to be colorful at night. White flowers also reflect moonlight. Why they flower at night is because they avoid competition from day blooming pollinators. It’s nature’s win-win situation for plants as well as pollinating animals. 

Q. How does the bee know which flower has nectar?

is a sugar-rich liquid produced by plants in glands called nectaries. Nectar is produced by plants to attract pollinators including bees. Besides, nectar-bearing flowers are attractive and produce fragrance as well. These features attract bees to such flower-bearing plants. 

Q. Why does cactus have so many thorns?

The cactus thorns are actually modified leaves. This modification is meant to reduce the transpiration rate. Cactus grows in deserts where water is a limiting factor. If cactus has normal leaves, the loss of water through transpiration would be more. That’s why the leaves modified into spines and the stem modified to a flattened green structure responsible for photosynthesis. Besides, the thorns protect plants from animals.

Q. How does the chick recognize her own mother?

The chick recognizes her own mother through the process called imprinting that involves vision, hearing, and olfaction along with touch. Once the egg hatches and the chicks come out – they see the mother, her smell and sound get imprinted within 24 to 48 hours. This type of learning is limited to discrete and sensitive periods in an animal’s life, often when the animal is very young and it has long-lasting effects. Imprinting usually means that the animals learn to identify; approach and follow something or someone, usually a parent. And that helps the animal to find food, shelter, and warmth, etc. Chicks show this type of learning within the first 48 hours after hatching. 

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