Inheritance Patterns | Reading Pedigree Charts

Download the free flowchart

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DISCLAIMER: This video and description contains affiliate links, which means that if you click on some of the product links, I’ll receive a small commission. This helps support the channel and allows us to continue to make videos like this. Thank you for your support!

Thanks for stopping by, today we are going to discuss how to determine inheritance patterns, so essentially how to read a pedigree chart. Like this one. If you are unfamiliar with pedigree charts or Mendelian genetics, you should watch some other videos before this one.

We are going to create a flowchart to solve pedigrees, so you’ll simply take any given pedigree chart through a series of questions until you determine the inheritance pattern.

And a note here, this flowchart we are going to build has a high degree of accuracy, but is not foolproof, the random nature of genetics make it impossible to be 100%.

So let’s get started, the first two questions you’ll ask are, Are only males affected? AND are all sons of an affected father affected?

If the answer is yes, then the pattern is Y linked, meaning a genetic disorder affiliated with the y chromosome. Only males possess a Y chromosome, so that means all males receive their Y chromosome from their father. A Y linked trait will never show up in males without affected father. If you reach this point, you have your solution.

If the answer is no,

Then we ask if there are there any cases were affected children do not have at least one affected parent.

If yes, it’s recessive though we don’t know what type. Being recessive, they must have two affected alleles in order to express the disorder, therefore, an affected child can have unaffected parents because they're both carries. However, it is possible that their parents could still be affected.

If the answer is no, then it is a dominant disorder, and thus an affected child must have an affected parent. You should note that dominant patterns usually see someone affected in every generation in each affected linage, this means that once you see an affected parent, you will usually see it in every generation thereafter. It doesn’t skip generations very often.

Moving down the recessive line we need to ask two more questions.

Are all sons of affected mother infected? And are more males affected in general?

If yes, it is X-linked recessive, meaning it’s attached to the X chromosome, since males only have one X chromosome, they are more likely to show, whereas females have two Xs, so a good one can mask the mutated one. Also, Males always receive their X chromosome from their mother, so if she is affected, she will have two X chromosomes with the mutation, and all sons are guaranteed to end up with it.

If the answer is no, then it is autosomal recessive by default. Essentially, males and females are affected evenly, and affected mothers have unaffected sons.

Moving on down the dominant line, we ask

Are all of the daughters of an affected father affected?

If yes, then it is X linked dominant, males only have one X chromosome, which goes to their daughter, so all their daughters will have that mutation.

If no, then it is autosomal dominant by default. If there is a case where an affected father has an unaffected daughter, or an affected daughter has an unaffected father, you know it can’t be X linked, because the father only has one X and that will always to go to the daughter.

So this is the whole flow chart, eventually I’ll make a website and have a downloadable PDF available. I’ll link that in the comments whenever I get to making it. In the meantime, subscribe to my channel so that you’re around when I do create my website.

Thanks for watching, I’ll catch you next time.

[gropemygoat]

managed to teach me more in 3 mins than an entire hour of lectures from my professor. NICE!

[dubidubidapdap]

I've watched other videos to learn inheritance patterns but this is the only video that made me understand the topic SO EASILY.

[beatricemartin]

Fter being so confused, this video was so helpful and efficient in explaining modes of inheritance. Thank you!

[dakshkhillan]

Thank you so so much for these videos.... I'm from India, preparing for medical entrance (NEET) and these really helped ! I immediately subbed ! Keep making these videos

[arinna]

Thank you so much for this oversimplified yet amazingly helpful information, the flowchart was especially helpful, really really thank you!

[elisekate]

Thank-you so much! Cramming for an honors bio test tommorow

[yshysdiary]

wow, this saved me from those trial and error sessions, thanks!

[dennishuang]

It would have been more helpful to have a pedigree chart beside your explanation. It's really confusing me what you are explaining without it.

[xfader]

Went through most of your videos and dudeee your content looks so promising! I just subbed! :D
PS Can you make more of the Biotech stuff like Translation and all?

[Sherirose]

Can this be applied to Pathophysiology? Thanks for your videos

[Jameshshwh]

Teacher i have a question what is the difference between patterns of inheritance and pedigree because their definition are a little same is there any relation between them or difference?

[racinerobinson]

but what if the expression of the gene is recessive, then wouldn't it make more sense for the parents to be heterozygous carriers and not homozygous recessive?

[cybilrichmond]

Did you ever make the pdf for this flowchart?

[ConnorRicks]

Could you make a video about the human genome, and what societal issues it can solve? That would be awesome.

[DkongTuber]

Are only males affected?
AND
Are all sons of an affected father affected?






The 2 questions just in case you need to copy and paste

[lilyrosedaisy]

Good video, but it should be x-linked not y-linked