Heredograma - Brasil Escola

Summary

In this educational video, Professor Fred explains the importance of heredograms in genetics, focusing on their role in tracking hereditary traits. He covers the basic symbols and structures used in heredograms, such as male and female representations, the meaning of affected or unaffected individuals, and the distinction between dominant and recessive traits. Fred also delves into real-life genetic examples, like tongue rolling and ear lobe attachment, explaining how these traits follow dominant or recessive inheritance patterns. He emphasizes the value of heredograms in understanding genetic disorders and their sex-linked patterns.

Takeaways

• 😀 Heredograms (also known as genealogies) are used to visualize genetic inheritance patterns within families or animal populations.
• 😀 A heredogram helps identify whether a trait is dominant or recessive, and if it is linked to a specific sex.
• 😀 Symbols in heredograms represent sex: squares (♂) for males, circles (♀) for females, and diamonds (◊) for individuals with indeterminate sex.
• 😀 Inherited traits in heredograms are shown with shaded symbols, meaning the trait is present, while unshaded symbols indicate normal individuals without the trait.
• 😀 Marriages are represented by a line connecting a square (♂) and a circle (♀), with consanguineous marriages (e.g., cousins) marked by double horizontal lines.
• 😀 The children of a marriage are represented by vertical lines descending from the couple, with each child shown by a square (♂) or circle (♀).
• 😀 Twins can be represented in two ways: monozygotic (identical) twins are connected by a triangle shape, while dizygotic (fraternal) twins are not.
• 😀 A non-childbearing marriage is indicated with two horizontal lines after the vertical line, suggesting infertility or no children yet.
• 😀 To identify whether a trait is dominant or recessive, check for whether the characteristic appears in a higher or lower frequency in the offspring.
• 😀 Dominant traits show more frequent occurrences in offspring, whereas recessive traits appear less often and typically in homozygous recessive individuals.
• 😀 Real-life examples of dominant and recessive traits include tongue rolling (dominant) and attached earlobes (recessive).

Q & A

What is the purpose of constructing a heredogram?

A heredogram, also known as a genealogical tree, is used to represent the inheritance of certain traits within a family or group. It helps visualize whether a trait is dominant or recessive, and whether it's sex-linked, aiding in the understanding of genetic inheritance patterns.

How do you represent male and female individuals in a heredogram?

In a heredogram, males are represented by squares, while females are represented by circles. If the sex of an individual is unknown, a diamond shape is used to indicate an indeterminate sex.

What does it mean when an individual is shaded in a heredogram?

When an individual is shaded in a heredogram, it indicates that the individual carries the trait being studied. This does not necessarily mean the individual is 'affected' by a disease or condition but rather that the trait is present.

What is the difference between monozygotic and dizygotic twins in a heredogram?

Monozygotic (identical) twins are represented by two connected symbols (squares or circles) with a horizontal line between them, indicating that they share the same genotype because they come from a single fertilized egg. Dizygotic (fraternal) twins are shown with separate symbols without the connecting line, and they may or may not be of the same sex.

How is a consanguineous marriage represented in a heredogram?

A consanguineous marriage, which refers to a marriage between close relatives, is represented by a horizontal line connecting two individuals, with two lines between them. This indicates a genetic relationship between the individuals, such as cousins marrying.

What does it indicate when there are no descendants in a marriage shown in a heredogram?

When a marriage is shown with no descendants, it indicates that the couple did not have children. This could be due to infertility or the couple not yet having children.

How can you identify whether a trait is dominant or recessive in a heredogram?

To identify if a trait is dominant or recessive, observe the frequency of affected individuals. A dominant trait will appear more frequently, as it can be expressed in both heterozygous and homozygous individuals. A recessive trait will appear less frequently, as it requires both alleles to be recessive (homozygous recessive) for expression.

What is the significance of generations marked with Roman numerals in a heredogram?

Generations are typically marked with Roman numerals in a heredogram to indicate the family lineage. For example, I for the grandparents, II for the parents, and III for the children. This helps trace the inheritance of traits through multiple generations.

What does it mean when a heredogram shows a child who is unaffected by a trait that both parents possess?

If both parents have the trait but one child does not, it suggests that the trait is recessive. The parents are likely heterozygous carriers, and the child would have inherited a recessive allele from both parents, resulting in the child not expressing the trait.

Can you give an example of a human characteristic that follows the rules of genetic dominance?

An example of a human characteristic that follows the rules of genetic dominance is the ability to roll the tongue. The dominant allele for this trait allows individuals to roll their tongues, whereas individuals with two recessive alleles cannot do so.