heredity

what is heredity

ผลการค้นหารูปภาพสำหรับ heredity

Heredity also called inheritance or biological inheritance is the passing on of traits from parents to their offspring; either through asexual reproduction or sexual reproduction, the offspring cells or organisms acquire the genetic information of their parents. Through heredity, variations between individuals can accumulate and cause species to evolve by natural selection. The study of heredity in biology is genetics.

what are trait

Identical twins have exactly the same DNA, but they are not exactly alike. Each twin has his or her own personality, talents, likes, and dislikes. There are even diseases that appear in one twin but not the other, including arthritis, diabetes, autism, schizophrenia, cancer, and many others. The differences between identical twins don’t come from DNA—they all come from external factors.

Scientists often study twins to understand how genes and the environment work together to affect traits. They compare traits in identical twins, who have identical DNA, and fraternal twins, who share half their DNA, just like any siblings. If a characteristic appears more frequently in identical twin pairs than in fraternal twin pairs, then it has an inherited component.

With dimples

Windswept Cary Grant photo with annotation arrows.jpg

A dimple (also known as a gelasin)[1] is a small natural indentation in the flesh on a part of the human body, most notably in the cheek or on the chin.

Cheek dimples when present, show up when a person makes a facial expression, such as smiling, whereas a chin dimple is a small line on the chin that stays on the chin without making any specific facial expressions. Dimples may appear and disappear over an extended period;[2] a baby born with dimples in their cheeks may lose them as they grow into a child due to their diminishing baby fat.[3] They are often associated with youth and beauty (e.g. Chinese culture believes that cheek dimples are a good luck charm)[4] and are seen as an attractive quality in a person’s face, accentuating smiles.[4]

ผลการค้นหารูปภาพสำหรับ eyelid

An eyelid is a thin fold of skin that covers and protects an eye. The levator palpebrae superioris muscle retracts the eyelid, exposing the cornea to the outside, giving vision. This can be either voluntarily or involuntarily. The human eyelid features a row of eyelashes along the eyelid margin, which serve to heighten the protection of the eye from dust and foreign debris, as well as from perspiration. “Palpebral” (and “blepharal”) means relating to the eyelids. Its key function is to regularly spread the tears and other secretions on the eye surface to keep it moist, since the cornea must be continuously moist. They keep the eyes from drying out when asleep. Moreover, the blink reflex protects the eye from foreign bodies.

Have ear lobes

The human earlobe (lobulus auriculae) is composed of tough areolar and adipose connective tissues, lacking the firmness and elasticity of the rest of the auricle (the external structure of the ear). In some cases the lower lobe is connected to the side of the face. Since the earlobe does not contain cartilage[1] it has a large blood supply and may help to warm the ears and maintain balance. However, earlobes are not generally considered to have any major biological function.[2] The earlobe contains many nerve endings, and for some people is an erogenous zone.

The zoologist Desmond Morris in his book The Naked Ape (1967) conjectured that the lobes developed as an additional erogenous zone to facilitate the extended sexuality necessary in the evolution of human monogamous pair bonding.[3]

hair whorl

Baby hairy head DSCN2483.jpg

A hair whorl is a patch of hair growing in a circular direction around a visible center point. Hair whorls occur in most hairy animals, on the body as well as on the head. Hair whorls, also known as crowns, swirls, or trichoglyphs, can be either clockwise or counterclockwise in direction of growth.

Hair whorls on the head (parietal whorls) have been studied by some behaviorists. Most people have clockwise scalp hair-whorls. Parietal whorls which are considered to be normal scalp patterns could be a single whorl or double whorls. Cases of triple parietal whorls are less common but do not necessarily indicate abnormality.[citation needed]

Amar J. S. Klar conducted research to see if there was a genetic link between handedness and hair-whorl direction. He found that 8.4% of right-handed people and 45% of left-handed people have counterclockwise hair-whorls. His research suggested that a single gene may control both handedness and hair-whorl direction.[1] However, Klar’s research methodology in this and other studies has been questioned.[2]

Another result concerning handedness of the progeny of discordant monozygotic twins suggests that left handed people are one gene apart from right handed people. Together, these results suggest (1) that a single gene controls handedness, whorl orientation, and twin concordance and discordance and (2) that neuronal and visceral (internal organs) forms of bilateral asymmetry are coded by separate sets of genetic pathways. [3]

Tongue rolling

ผลการค้นหารูปภาพสำหรับ Tongue rolling

Tongue rolling is the ability to roll the lateral edges of the tongue upwards into a tube. The tongue’s intrinsic muscles allow some people to form their tongues into specific shapes. Popular belief holds that variation in this ability is the result of genetic inheritance. Rolling the tongue into a tube shape is often described as a dominant trait with simple Mendelian inheritance, and it is commonly referenced in introductory and is genetic biology courses.[1]

There is little laboratory evidence supporting the hypothesis that tongue rolling is inheritable and dominant. In 1940, Alfred Sturtevant observed that ~70% of people of European ancestry could roll their tongues and the remaining ~30% could not do it.[2] A 1975 twin study found that identical twins were no more likely than fraternal twins to both have the same phenotype for tongue rolling.[3]

Cloverleaf tongue – 4 times

Cloverleaf tongue is the ability to fold the tongue in a certain configuration with multiple bends. To the extent to which it is genetic, it is probably a dominant trait distinct from tongue rolling.[3]

 

 

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