Heredity

What is heredity?

heredity

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Heredity 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 traitผลการค้นหารูปภาพสำหรับ what are traits

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.

5 heredity example

1.Eye color

 

Eye color is a polygenic phenotypic character determined by two distinct factors: the pigmentation of the eye‘s iris[1][2] and the frequency-dependence of the scattering of light by the turbid medium in the stroma of the iris.[3]:9

In humans, the pigmentation of the iris varies from light brown to black, depending on the concentration of melanin in the iris pigment epithelium (located on the back of the iris), the melanin content within the iris stroma (located at the front of the iris), and the cellular density of the stroma.[4] The appearance of blue and green, as well as hazel eyes, results from the Tyndall scattering of light in the stroma, a phenomenon similar to that which accounts for the blueness of the sky called Rayleigh scattering.[5] Neither blue nor green pigments are ever present in the human iris or ocular fluid.[3][6] Eye color is thus an instance of structural color and varies depending on the lighting conditions, especially for lighter-colored eyes.

The brightly colored eyes of many bird species result from the presence of other pigments, such as pteridinespurines, and carotenoids.[7] Humans and other animals have many phenotypic variations in eye color.[8] The genetics of eye color are complicated, and color is determined by multiple genes. So far, as many as 15 genes have been associated with eye color inheritance. Some of the eye-color genes include OCA2 and HERC2.[9] The earlier belief that blue eye color is a simple recessive trait has been shown to be incorrect. The genetics of eye color are so complex that almost any parent-child combination of eye colors can occur.[10][11] However, OCA2 gene polymorphism, close to proximal 5′ regulatory region, explains most human eye-color variation.

2.Hair color

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Hair color is the pigmentation of hair follicles due to two types of melanineumelanin and pheomelanin. Generally, if more eumelanin is present, the color of the hair is darker; if less eumelanin is present, the hair is lighter. Levels of melanin can vary over time causing a person’s hair color to change, and it is possible to have hair follicles of more than one color on the same person. Particular hair colors are often associated with ethnic groups, while gray or white hair is associated with age.

 

 

3.Dimple

ผลการค้นหารูปภาพสำหรับ Dimple

3.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.

4.Human skin color

ผลการค้นหารูปภาพสำหรับ human skin color

Extended Coloured family from South Africa showing some spectrum of human skin coloration

Human skin color ranges in variety from the darkest brown to the lightest hues. An individual’s skin pigmentation is the result of genetics, being the product of both of the individual’s biological parents‘ genetic makeup, and exposure to sun. In evolution, skin pigmentation in human beings evolved by a process of natural selection primarily to regulate the amount of ultraviolet radiation penetrating the skin, controlling its biochemical effects.[1]

The actual skin color of different humans is affected by many substances, although the single most important substance is the pigment melanin. Melanin is produced within the skin in cells called melanocytes and it is the main determinant of the skin color of darker-skinned humans. The skin color of people with light skin is determined mainly by the bluish-white connective tissue under the dermis and by the hemoglobin circulating in the veins of the dermis. The red color underlying the skin becomes more visible, especially in the face, when, as consequence of physical exercise or the stimulation of the nervous system (anger, fear), arterioles dilate.[2] Color is not entirely uniform across an individual’s skin; for example, the skin of the palm and the sole is lighter than most other skin, and this is especially noticeable in darker-skinned people.[3]

5.Earlobe

ผลการค้นหารูปภาพสำหรับ ติ่งหู

 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.

 

 

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