Punnett Squares and Sex-Linked Traits (OLD VIDEO)
Summary
TLDRThis video script delves into the underappreciated role of platelets in blood clotting and the impact of hemophilia, a sex-linked recessive disorder. It explains the genetic basis of hemophilia, highlighting the difference between sex chromosomes and autosomes. The script clarifies how hemophilia is inherited, with a focus on the X chromosome's role and the higher likelihood of males being affected. It also outlines the process of creating a sex-linked Punnett square to predict offspring genotypes, emphasizing the increased risk for male children.
Takeaways
- 🩸 Platelets are crucial for blood clotting and preventing excessive bleeding.
- 🔪 Hemophilia is a disorder that affects the ability of blood to clot, making even minor cuts dangerous.
- 💊 Treatments for hemophilia have significantly improved over time, offering better outcomes for those affected.
- 🧬 Hemophilia is a sex-linked recessive trait, meaning it is inherited differently than typical Mendelian traits.
- 🧬 Sex chromosomes are X and Y, with females typically having XX and males having XY.
- 🧬 The X chromosome is larger and contains more genes than the Y chromosome, which is why most sex-linked traits are found on the X.
- 🔠 Hemophilia is represented by the alleles H (normal) and h (hemophilia), with hemophilia being recessive.
- 👩👧👦 A female can be a carrier of hemophilia with the genotype XHXh, but will not show symptoms unless she has XhXh.
- 👨👦 A male can only have hemophilia if his genotype is XhY, as he does not have a second X chromosome to potentially carry a dominant allele.
- 👶 When two parents without hemophilia but with one carrier have children, there is a 25% chance a male child will inherit hemophilia.
- 🧬 Sex-linked disorders like hemophilia and color blindness are more common in males due to their single X chromosome.
Q & A
What are platelets and why are they important?
-Platelets are fragments of cytoplasm that play a crucial role in the blood clotting process, helping to stop bleeding when we get injured.
What is hemophilia and how does it affect the body?
-Hemophilia is a genetic disorder that impairs the blood's ability to clot, leading to continuous bleeding even from minor injuries due to the dysfunction of platelets.
How have treatments for hemophilia evolved over time?
-Treatments for hemophilia have greatly improved, offering better outcomes for individuals with the disorder, although the script does not detail the specific advancements.
What is the difference between sex-linked and Mendelian genetic traits?
-Sex-linked traits, such as hemophilia, are associated with the sex chromosomes and follow a different pattern of inheritance compared to Mendelian traits, which are governed by the principles of dominance and recessiveness on autosomes.
What are sex chromosomes and how do they differ from autosomes?
-Sex chromosomes, designated as X and Y, determine an individual's sex and are distinct from autosomes, which are the remaining chromosomes that do not determine sex.
Why are the X and Y chromosomes named so, and what does their shape have to do with it?
-The X and Y chromosomes are named as such due to historical reasons and their shape does not correspond to their names; the Y chromosome is not shaped like 'Y', and the X chromosome is not shaped like 'X'.
What determines an individual's sex based on their chromosomes?
-An individual with two X chromosomes (XX) is female, while an individual with one X and one Y chromosome (XY) is male.
What are sex-linked traits and why are most of them found on the X chromosome?
-Sex-linked traits are genetic traits located on the sex chromosomes, with most being on the X chromosome because it is larger and contains more genes than the Y chromosome.
How is hemophilia represented in genetic notation, and what does this notation imply?
-Hemophilia is represented by the lowercase allele 'h', indicating its recessive nature, and is placed as a superscript on the sex chromosomes to denote its sex-linked inheritance.
What are the possible genotypes for a female who does not have hemophilia?
-A female who does not have hemophilia could have the genotypes XHXH or XHXh, as the presence of at least one dominant XH allele prevents the expression of the recessive disorder.
How can you determine the risk of a child inheriting hemophilia from carrier parents using a Punnett square?
-By identifying the genotypes of carrier parents (e.g., XHXh for the mother and XHY for the father) and performing a sex-linked Punnett square, you can predict the offspring's genotypes and phenotypes, including the risk of hemophilia.
Outlines
🩸 Platelets and Hemophilia Genetics
This paragraph introduces the crucial role of platelets in blood clotting and the medical condition hemophilia, which impairs this function. It explains hemophilia as a sex-linked recessive trait, contrasting it with typical Mendelian genetics due to its association with sex chromosomes. The explanation delves into the basics of human chromosomes, differentiating the 46 chromosomes into autosomes and sex chromosomes, labeled X and Y. It clarifies common misconceptions about the shape of these chromosomes and their naming. The paragraph further explains sex-linked traits, predominantly found on the X chromosome due to its larger size and gene count compared to the Y chromosome. Hemophilia, represented by alleles 'H' for non-hemophilia and 'h' for hemophilia, is detailed with genotype examples for both males and females, illustrating how the condition can manifest and be inherited.
🧬 Sex-Linked Inheritance of Hemophilia
The second paragraph focuses on the inheritance patterns of hemophilia, a sex-linked recessive disorder. It outlines the process of creating a sex-linked Punnett square to predict the offspring's genotype and phenotype when one parent is a carrier and the other is unaffected. The explanation includes the genotypes of potential parents, the steps to perform the cross, and the formatting considerations. The paragraph concludes with the probability of offspring being born with or without hemophilia, emphasizing the higher likelihood of males inheriting the disorder due to having only one X chromosome. It also makes a comparison to other sex-linked recessive disorders such as color blindness and ends with a signature reminder from the Amoeba Sisters to stay curious.
Mindmap
Keywords
💡Platelets
💡Hemophilia
💡Cytoplasm
💡Sex-linked recessive trait
💡Chromosomes
💡Sex chromosomes
💡Alleles
💡Genotype
💡Phenotype
💡Punnett square
💡Carrier
Highlights
Platelets are underappreciated fragments of cytoplasm that help stop bleeding and aid in blood clotting.
Hemophilia is a disorder affecting platelets, where even a basic cut can be dangerous due to continuous bleeding.
Modern treatments have significantly improved outcomes for individuals with hemophilia.
Hemophilia is a sex-linked recessive trait, differing from typical Mendelian genetic inheritance.
Humans have 46 chromosomes, with two being sex chromosomes, X and Y, unrelated to their shape.
Everyone has at least one X chromosome; two Xs indicate female, while an X and a Y indicate male.
Sex-linked traits, like hemophilia, are located on the sex chromosomes, predominantly the X due to its size and gene count.
Hemophilia is represented by alleles 'H' for no hemophilia and 'h' for having hemophilia, with 'h' being recessive.
A woman without hemophilia can have genotypes XHXH or XHXh, as the dominant allele will show the phenotype.
A female with hemophilia must have the genotype XhXh, as no dominant allele is present.
For males, not having hemophilia means having the genotype XHY, as the Y chromosome does not carry the trait.
A male with hemophilia has the genotype XhY, as there is no second X chromosome to provide a dominant allele.
Males cannot be carriers of hemophilia due to the lack of a second X chromosome.
If both parents do not have hemophilia but the mother is a carrier, a sex-linked Punnett square can predict offspring genotypes.
The mother's genotype as a carrier is XHXh, and the father's, if unaffected, is XHY.
The offspring genotype ratio from such a cross would be predictable, with a 75% chance of being hemophilia-free and a 25% chance of having hemophilia.
Boys are more likely to inherit sex-linked recessive disorders like hemophilia due to having only one X chromosome.
The video by the Amoeba Sisters educates on the importance of understanding genetic disorders like hemophilia.
Transcripts
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Would you like to know one of the most underappreciated pieces of cytoplasm out there?
Platelets.
We take for granted the function of our platelets, which are fragments of cytoplasm that help
stop us from bleeding.
They help our blood to clot when we get hurt.
But there is a disorder called hemophilia that can affect those platelets and even a
basic cut could be dangerous for them because they could bleed continuously.
We have many treatments for the symptoms of Hemophilia now that have greatly improved
outcomes with this disorder.
Although it wasn’t always that way.
Hemophilia is a sex-linked, recessive trait which means it is different from basic Mendelian
genetic problems.
We still use the terms dominant and recessive for alleles---but this time---those alleles
are on sex chromosomes.
This is the case with sex-linked traits.
What is a sex chromosome?
Recall that humans have 46 chromosomes.
Chromosomes are made up of DNA and protein.
They contain your genes.
Well two of your 46 chromosomes -they are called the sex chromosomes.
In a karyotype, it is usually the last two chromosomes that are the sex chromosomes.
The sex chromosomes are called X and Y chromosomes but it has nothing to do with the shape of
the chromosome.
That’s kind of confusing but please don’t think that Y chromosomes are shaped like a
Y and X chromosomes are shaped like a X.
That used to always confuse me---that has nothing to do with their name.
The reason they got those names is actually kind of interesting so to the Google for that.
Everyone has a X chromosome.
But if you have another X chromosome---meaning you have two X chromosomes---you are female.
And if you have a Y chromosome---meaning you have a X and Y chromosome---you are male.
There are also genetic disorders where you can have extra copies of sex chromosomes but
we are not going into that for this clip.
Sex-linked traits are traits that are specifically on the sex chromosomes.
Most sex-linked traits tend to be on the X chromosome, because it is larger than the
Y chromosome and contains more genes than the Y chromosome.
The disorder hemophilia is like this.
We will use the letter “H” to represent an allele for not having hemophilia and a
letter “h” to represent an allele for having hemophilia.
Hemophilia is a recessive disorder, which is why it is being represented by a lowercase
letter h.
Only, it must be placed on the sex chromosomes as a superscript.
Like an exponent.
Let me explain what I mean by that.
A woman that does not have hemophilia could have the genotype XHXH or XHXh.
Because as long as she’s got at least one dominant allele---that dominating allele---will
be what shows.
So no hemophilia, since again, hemophilia is a recessive disorder.
The only way for her to have hemophilia would be the genotype XhXh.
Because only when there is no dominant present will that recessive show up, at least in this
type of trait.
For a male to not have hemophilia, his genotype would have to be XHY.
Notice how I didn’t put anything on the Y chromosome---again, most sex linked traits
are on the X chromosome.
If he has the genotype XhY, then he has hemophilia.
He doesn’t have two X chromosomes, so in this disorder, he either has it or he doesn’t.
There is no heterozygous genotype for the male so he cannot be a carrier.
So let’s say two people that do not have hemophilia have children.
However, let’s say the woman is a carrier.
That means she is heterozygous.
How do you do a sex-linked Punnett square cross for this kind of trait?
Step 1) Identify the genotypes of the parents.
So the mother is XHXh.
She doesn’t have hemophilia because of the dominant allele present but she is a carrier.
The male, if he does not have hemophilia, must be XHY.
There’s no other option for him.
Step 2) Place one parent on the top, outside of the square like this.
Place the other parent on the left, outside of the square, like this.
Step 3) Cross them!
For formatting purposes, place X chromosomes before Y.
You also write any sex chromosomes with dominant letters first.
The results you get in the squares would be the offspring---the babies.
The genotype ratio could be written out like this.
The phenotype ratio—remember that these are the traits---can be written out that there
is a 75% chance that a child will be born without hemophilia and a 25% chance that a
child would have hemophilia, for this boy here.
Notice that in this type of example of a sex linked recessive disorder---boys are more
likely to inherit this disorder---because they only have one X chromosome.
This is true for many other sex linked recessive disorders, such as color blindness.
Well that’s it for the amoeba sisters and we remind you to stay curious!
Voir Plus de Vidéos Connexes
Punnett Squares and Sex-Linked Traits (UPDATED)
Sex linked Genetic diagrams
Example punnet square for sex-linked recessive trait | High school biology | Khan Academy
NON-MENDELIAN GENETICS: SEX-LINKED TRAITS | SEX INFLUENCED TRAITS | SEX-LIMITED TRAITS | SCIENCE 9
Genetics: Sex-limited Traits
Hemophilia and Gene Therapy
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