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3.4. Human genetics

Human genetics

In humans, the transmission mechanisms of hereditary traits occur in the same way as in other living beings. Genes are transmitted from parents to descendants, and the differences between individuals are a consequence of their genes from the influence of the environment. Genetic characteristics can vary depending on how the environment influences, for example, improving with a healthy lifestyle, but the effects produced on the phenotype due to the environment alone are not transmitted to the offspring.

Although the same experiments cannot be done in people as in animals, since crosses cannot be planned to check what the offspring is like, the family history of some characteristics or alterations that appear in people of the same family can be analyzed.

Heredity in the human species

Humans have 46 chromosomes, 23 pairs, in all somatic cells, since we are diploid (2n). The only haploid cells (n) are the gametes (ovules and sperm), which only have 23 chromosomes, since when they unite in fertilization, they will give rise to an individual with all 46 chromosomes (2n). In the gametes are the genes with the necessary information for the hereditary characteristics of the new individual.

Nonsex chromosomes, common in both sexes, are called autosomes. The sex chromosomes or heterocromosomas are homologous in females (XX) and different in males (XY). The Y chromosome is much smaller than the X chromosome and contains fewer genes than the X chromosome.

The karyotype is the set of all the chromosomes of the cell. In it you can see their number and the appearance (in metaphase) of the chromosomes that characterize the species. By analyzing the karyotype, numerical and structural abnormalities can be analyzed.

When represented graphically, in drawing or photograph, karyotype, with numbered and ordered pairs of homologous chromosomes sizes and shapes, the obtained cariogram or ideogram.

People have many characters that differentiate us, such as facial features, hair color, eyes, height, etc. These characters can be of two types:

  • Characters acquiredThey are not transmitted to offspring, since they appear as a consequence of interaction with the environment. For example, if a person gains a lot from having an unhealthy diet, or has highly developed muscles from doing a lot of sports, these characteristics will not be passed on to the offspring .
  • Hereditary characters, yes that are transmitted to the offspring, since they are genetically determined.

Characters can also be classified according to how they differ from others. Thus, they are distinguished:

  • Quantitative characters, when the differences between individuals are small and gradual. For example, hair color, skin color, height, etc. They are usually influenced by the environment, which conditions the expression of the genotype.
  • Qualitative characters, when the differences are notable or discontinuous. For example, albinism, which appears or does not appear, or blood groups, which are A, B, AB or 0.

Some of these hereditary qualitative characters that appear in humans are the following:

Dominant Recessive
Roll-up tongue in "U" Non-roll-up tongue in "U"
Rh + blood group Rh blood group -
Blood groups A and B Blood group 0
hair curly Straight hair
Dark colored hair Light colored hair
Dark colored eyes Light colored eyes
Thick lips Fine lips
Long eyelashes Short eyelashes
Hair in widow's peak Hairless in widow's peak
Ear with detached lobe Ear with attached lobe
Dwarfism Normal height
Brachydactyly Toes of normal length
Huntington's chorea No Huntington's chorea
Normal pigmentation Albinism
Normal clotting Hemophilia
Normal vision for colors colour blindness
Normal ear Deaf mute
Polydactyly Five fingers

La capacidad de enrollar la lengua se debe a un gen dominante.The ability to " carry your tongue " or "roll your tongue into a" U "is due to a dominant allele..


         

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Biology and Geology teaching materials for Compulsory Secondary Education (ESO) and Baccalaureate students.