Herança Sexual - Aula 14 - Módulo II: Genética | Prof. Gui

Summary

In this biology lesson, Professor Guilherme delves into the topic of sex-linked inheritance, exploring the genetic traits linked to the X and Y chromosomes. He covers disorders such as hemophilia, colorblindness, and Duchenne muscular dystrophy, explaining how these are inherited through recessive genes on the X chromosome. He also touches on sex-influenced traits like baldness, where gender influences the expression of the trait. Using real-world examples, he guides viewers through the complexities of genetic inheritance, emphasizing the importance of understanding both X-linked and Y-linked inheritance patterns in genetics.

Takeaways

• 😀 Understanding X-linked inheritance is essential when studying genetic diseases like hemophilia, color blindness, and muscular dystrophy.
• 😀 In X-linked inheritance, the gene is located on the X chromosome, and its corresponding allele doesn't have a match on the Y chromosome, affecting males more severely.
• 😀 Sex-limited inheritance, such as traits on the Y chromosome, only manifests in males, like in the case of hypertrichosis auricular (excessive hair growth on the ears).
• 😀 Sex-influenced inheritance, such as male-pattern baldness, is an autosomal trait influenced by the presence of male hormones, like testosterone.
• 😀 Mendel's laws of inheritance apply to autosomal traits, but sex-linked traits differ significantly due to the genetic make-up of sex chromosomes.
• 😀 A carrier of X-linked recessive traits, such as color blindness, only carries the gene and doesn't express the trait unless both X chromosomes are affected.
• 😀 Female carriers of X-linked recessive traits pass on the gene to their offspring, but males are more often affected due to having only one X chromosome.
• 😀 An individual with an X-linked recessive trait, like hemophilia, has one affected X chromosome, while a female with the trait must have both X chromosomes affected.
• 😀 A typical genetic cross can predict the probability of offspring inheriting X-linked traits, helping understand the chances of a child having traits like color blindness.
• 😀 Understanding how testosterone affects the manifestation of traits like baldness in men vs. women is key to grasping the concept of sex-influenced inheritance.

Q & A

What is the main topic of the video script?

The main topic of the video is genetic inheritance, specifically focusing on sex-linked inheritance, inheritance restricted to sex, and inheritance influenced by sex.

What are the three types of inheritance patterns discussed in the video?

The three types of inheritance patterns discussed are sex-linked inheritance, inheritance restricted to sex, and inheritance influenced by sex.

What does 'sex-linked inheritance' refer to in genetics?

Sex-linked inheritance refers to characteristics determined by genes located on the X chromosome, specifically those located in the non-homologous regions, which do not have a corresponding gene on the Y chromosome.

Can women inherit sex-linked traits like hemophilia or color blindness?

Yes, women can inherit sex-linked traits like hemophilia or color blindness, but they typically need to inherit the defective gene from both parents to express the trait, as these conditions are usually recessive.

What is the difference between sex-linked inheritance and inheritance restricted to sex?

Sex-linked inheritance involves genes on the X chromosome, affecting both sexes, while inheritance restricted to sex occurs when the gene is located on the Y chromosome and thus only affects males.

What is a key characteristic of inheritance restricted to sex?

Inheritance restricted to sex occurs when a trait is determined by a gene on the Y chromosome, affecting only males. An example is hypertrichosis auricular, a condition that causes excessive hair growth in the ears.

What is inheritance influenced by sex, and how does it affect traits like male pattern baldness?

Inheritance influenced by sex refers to traits determined by autosomal genes whose expression is modified by the presence of sex hormones like testosterone. For example, male pattern baldness is influenced by the presence of testosterone, which makes the trait dominant in men but recessive in women.

How does the presence of testosterone affect the inheritance of male pattern baldness?

In men, the allele for male pattern baldness is dominant due to the presence of testosterone, while in women, the same allele is recessive due to lower testosterone levels. As a result, baldness manifests differently in men and women.

Why is the term 'carrier' considered problematic when referring to individuals with certain genetic conditions?

The term 'carrier' is problematic because it suggests that individuals with a genetic condition can 'drop' the condition. It is more appropriate to directly refer to individuals as having the condition, such as calling someone 'blind' rather than 'a carrier of blindness.'

What is the probability of a couple with one son and one daughter, both heterozygous for male pattern baldness, having two children who are both bald?

The probability is 3/16. For the male, the baldness gene acts dominantly, so there is a 3/4 chance of the son being bald. For the daughter, the baldness gene is recessive, so there is only a 1/16 chance of her being bald if she inherits two baldness alleles.