Genetics: Sex-limited Traits

Summary

This educational video delves into the concept of sex-limited traits in genetics, explaining that these traits, unlike sex-linked traits, are inherited on autosomes but only expressed in one sex. Using beards in goats as an example, the video clarifies that even though the dominant allele for a beard is present in both sexes, it manifests only in males. The presenter uses a Punnett square to illustrate the inheritance patterns, showing that while 75% of males will express the trait, no females will, emphasizing the importance of distinguishing between sex-limited and sex-linked inheritance.

Takeaways

• 🧬 Sex-limited traits are not inherited on sex chromosomes but on autosomes like any other trait.
• 🦙 Traits like beards in goats are expressed only in one sex, typically males, despite being dominant alleles.
• 🔍 In heterozygous males, the dominant allele for a sex-limited trait will be expressed, while in females, it will not be.
• 📊 Punnett squares for sex-limited traits are constructed the same as for normal traits, without considering sex chromosomes.
• 👦 Males with sex-limited traits will show the trait if they have at least one dominant allele, regardless of homozygosity.
• 👧 Females, even if they are heterozygous for a sex-limited trait, will not express the trait if it's limited to males.
• 🌟 The percentage of males expressing a sex-limited trait is the same as if the trait were normally inherited, with a 3:1 ratio for dominant alleles.
• 🚫 Females will not express a sex-limited trait, resulting in a 0:1 ratio for expression in females.
• 🧬 Understanding the difference between sex-influenced, sex-limited, and sex-linked traits is crucial for genetics.
• 📚 The concepts in the video are based on specific textbook material and may be referenced in various genetics classes.
• 📝 Baylor students have access to free tutoring services for genetics and other subjects, with sessions available online or in person.

Q & A

What are sex-limited traits?

Sex-limited traits are characteristics that are inherited on an autosome but are only expressed in one of the two sexes. They are not related to sex chromosomes (X and Y) and do not involve hemizygosity.

Why are sex-limited traits not inherited on sex chromosomes?

Sex-limited traits are not inherited on sex chromosomes because they are carried on autosomes, which are chromosomes that are not involved in determining the sex of an individual.

Can you give an example of a sex-limited trait?

An example of a sex-limited trait mentioned in the script is the presence of beards in goats, which are only expressed in males.

How is the expression of a sex-limited trait different in males and females?

In the case of sex-limited traits, even if a female has the dominant allele, the trait will not be expressed. For instance, a female goat with the 'bearded' allele will not have a beard.

What happens when a heterozygote male and female mate in terms of sex-limited traits?

When a heterozygote male and female mate, the sex-limited trait will be expressed in the male offspring if they inherit the dominant allele, but it will not be expressed in the female offspring, regardless of their genotype.

How does the Punnett square help in understanding the inheritance of sex-limited traits?

The Punnett square helps in visualizing the possible genotypes of offspring when two individuals with known genotypes mate. For sex-limited traits, the Punnett square shows the same genotypic ratios but the expression will differ between males and females.

What is the percentage of males that will have a sex-limited trait if it is inherited normally?

If a sex-limited trait is inherited normally, 75% of males will express the trait if the dominant allele is present, as shown by the 3:1 ratio in the Punnett square.

What is the difference in the expression of a sex-limited trait in females compared to males?

In females, a sex-limited trait will not be expressed at all, regardless of their genotype, because the trait is limited to males.

Why might a homozygous recessive male not show a sex-limited trait?

A homozygous recessive male will not show a sex-limited trait because the trait is dominant, and the absence of the dominant allele means the trait will not be expressed.

How can the information from this video script be applied to genetics studies?

The concepts and information from this video script can be applied to genetics studies by understanding the inheritance patterns of sex-limited traits and distinguishing them from other types of inheritance such as sex-linked traits.

What additional resources are available for students studying genetics as mentioned in the script?

For Baylor students, free tutoring services are available on the first floor of Sid Richardson, and 30-minute one-on-one tutoring sessions can be scheduled online or accessed during normal business hours.

Outlines

00:00

🧬 Sex-Limited Traits and Inheritance Basics

This paragraph introduces the concept of sex-limited traits, explaining that these traits are not inherited through sex chromosomes but rather on an autosome. The video script clarifies that sex-limited traits are expressed differently in males and females, using the example of a beard in goats that is only expressed in males. The dominant allele for this trait is expressed in males, even if a female has the same genotype, the trait will not be visible. The paragraph also discusses the inheritance patterns of these traits, emphasizing that while the genetic inheritance follows the same rules as any other autosomal trait, the expression is limited to one sex.

Keywords

💡Sex-limited traits

Sex-limited traits refer to characteristics that are expressed differently or only in one sex, despite being inherited in the same manner as any other autosomal trait. In the video, the concept is introduced to differentiate from sex-linked traits which are inherited on sex chromosomes. An example given is the beard in goats, which is a sex-limited trait expressed only in males, regardless of the genetic makeup.

💡Autosomes

Autosomes are all the chromosomes in a cell that are not sex chromosomes. They are the same in both males and females. The video script explains that sex-limited traits are inherited on autosomes, not on the sex chromosomes (X and Y), and this is why the trait expression is limited to one sex despite the genetic inheritance being the same for both sexes.

💡Dominant allele

A dominant allele is a version of a gene that will produce its effect when paired with a different version of the same gene, known as a recessive allele. In the context of the video, the dominant allele for a beard in goats is expressed in males, but not in females, even if they carry the same allele, illustrating the concept of sex-limited dominance.

💡Heterozygote

A heterozygote is an individual that has two different alleles for a particular gene. In the video, the script discusses a Punnett square for a heterozygote cross, which results in a 3:1 ratio of dominant to recessive phenotypes in the offspring, but with the sex-limited trait, only males will express the dominant phenotype.

💡Punnett square

A Punnett square is a diagram used to predict the genotypes and phenotypes of offspring from a particular cross. The video uses the Punnett square to demonstrate how the sex-limited trait of a beard in goats would be inherited and expressed in the offspring, showing a 3:1 ratio for males but all females not expressing the trait.

💡Homozygous recessive

Homozygous recessive refers to having two copies of the same recessive allele for a gene. In the video, it is mentioned that if an individual is homozygous recessive for a dominant trait, they will not express that trait, which is true for both sexes, but in the case of sex-limited traits, only the males would normally express the trait if they were not homozygous recessive.

💡Inheritance

Inheritance in genetics refers to the passing on of traits from parents to offspring. The video discusses how sex-limited traits are inherited in the same way as autosomal traits, but the expression of these traits is limited to one sex, which is a key point in understanding the concept of sex-limited inheritance.

💡Phenotype

Phenotype is the set of observable characteristics of an individual resulting from the interaction of its genotype with the environment. The video explains that the phenotype of a sex-limited trait, such as a beard in goats, will only be observed in the sex for which the trait is limited, despite the genotype potentially being present in both sexes.

💡Genotype

Genotype refers to the genetic makeup of an individual, including all of its genes. The video script uses the term to contrast with phenotype, explaining that even though a female goat may have the genotype for a beard (the sex-limited trait), it will not express this trait in its phenotype.

💡Sex chromosomes

Sex chromosomes are the chromosomes that determine the sex of an individual, typically denoted as X and Y in humans and many other mammals. The video clarifies that sex-limited traits are not inherited on sex chromosomes, which is an important distinction from sex-linked traits.

💡Tutoring

Tutoring is a form of academic support provided to students to help them understand and apply concepts they are learning. The video script ends with information about free tutoring services available to Baylor students, which is a service unrelated to the main topic of sex-limited traits but part of the video's content.

Highlights

The video discusses sex-limited traits, which are not inherited on a sex chromosome but on an autosome.

Sex-limited traits are expressed differently in males and females, even if they are inherited in a normal autosomal manner.

Beards in goats are used as an example of a sex-limited trait, expressed only in males.

The dominant allele for a sex-limited trait is expressed in males, but not necessarily in females, even if heterozygous.

Homozygous recessive individuals, regardless of sex, will not express the dominant sex-limited trait.

Punnett squares are used to determine the percentage of males with the sex-limited trait, similar to normal inheritance patterns.

In normal inheritance, 75% of individuals are expected to express the dominant trait, regardless of sex.

For sex-limited traits, the Punnett square shows the same genetic ratios but with expression limited to one sex.

Females do not express sex-limited traits, even if they carry the dominant allele.

The video emphasizes the importance of understanding the difference between sex-inherited and sex-limited traits.

Studying genetics requires the ability to differentiate between various types of inheritance patterns.

The video provides a reference to a specific textbook for further study on the concepts presented.

Free tutoring services are available for Baylor students on the first floor of Sid Rich.

Students can schedule a 30-minute one-on-one tutoring session or drop in during business hours.

More information about tutoring services can be found on the provided website.

Transcripts

alright guys so in this video we're

gonna be talking about sex-limited

traits and what's important about a

sex-limited trait the first thing I'm

gonna tell you it is not inherited on a

sex chromosome so we're not gonna look

at it with the X and the y we're not

gonna hemizygous males nothing like that

it's going to be inherited on an

autosome just like anything else that

could be on chromosome 12 for oh we care

what we're gonna see with stuff like

this is we're gonna see it a trait

inherited like a normal autosome but

what's gonna happen is it's only going

to be expressed in one of the two sexes

so in this case we're gonna look at we

could say something like a beard right

so beards were in goats we're gonna say

are only expressed in males and what

that means is that and bearded the beard

allele is the dominant allele here so

you're gonna see big a big a and the

dominant allele is going to be expressed

here in the male as we see it yes we

have a bearded male but here in females

even though that female is big a big a

you're gonna see if the female is not

gonna show it that's because this trait

is limited just to males so then we go

down to our heterozygote here and again

because it's a dominant trait our male

is going to show it but our female here

is not gonna show it again and then when

we go down here just like any other

trait if it's a dominant trait and

you're homozygous recessive you're not

going to show it that's why neither our

male nor female here are gonna have the

trait so we're gonna go through talk

about some beards on some goats whether

if as if it was inherited normally

versus if it was inherited in a sex

limited fashion like we see here so what

we're gonna answer here is what's the

percentage of males that are gonna have

this trait whether it's normal or sex

limited so first we're going to do

normal and I'm gonna follow my punnett

square just like normal here and what

we're gonna get just like you guys would

expect by now with a heterozygote being

crossing the heterozygote is it's a 1 to

2 to 1 so what that means is we're gonna

have because it's a dominant allele

we're gonna have 3 2 1

and three is going to be bearded and the

one is not and so what that tells us if

we're trying to answer the question

remember how what percentage of the guys

are gonna have it have the beard so in

this case we're gonna have three bearded

and that's regardless of whether it's a

male or female right because this was

normal inheritance so if we do the same

thing over here so if this was a guy

this was a girl it would regardless

would have a 75% chance of inheriting

the beard because this trait is

inherited in a normal fashion

if this trait were inherited is sex

limited fashion our punnett square would

look the exact same

but what we're actually going to see

here is the same percentage of males

right so males it's going to be three to

one bearded versus non but what are we

going to see in females because this

trait is limited this time to males what

we're actually going to see is that

females it's gonna be zero to four

bearded versus none so you guys can see

we do our punnett square the exact same

way we didn't worry about anything about

sex chromosomes or anything like that

because again sex limited traits are on

autism's they're not on your X&Y or your

sex chromosomes so what we're gonna see

is the males if it's a trait that's

limited to males it's gonna be inherited

completely normally that doesn't always

have the trait right if it's a dominant

allele and it's a homozygous recessive

animal or whatever then it's still not

gonna show the trait so just because

it's limited to males doesn't mean it's

always in males but our females here

this is where it's important if our tray

is limited to males then we're not going

to have any females that are gonna show

that trait and just to reiterate one

more time I know it can get confusing

because you've got sex inherited traits

we've got sex limited traits we've got

other stuff like that

and so we're going to touch on all that

stuff so just make sure you study it

enough it's where you can keep it

separated inside your head I hope you

found this video really helpful the

concepts and information presented in

these videos will be sure no matter what

genetics class you were taking however

the concepts in this video are

referencing material from this specific

textbook remember if you are currently

enrolled Baylor student we offer free

tutoring on the first floor of Sid rich

you may schedule a free 30-minute

one-on-one tutoring session online or

just drop in during normal business

hours for more information about our

services please visit our website