Pedigrees, Gender and X-Linked Traits

Lesson Objectives

• Minds ON• Success Criteria from last week• Friday’s Recap • Pedigrees, Gender and X-Linked

Traits• Quiz Take Up• Disputed Maternity Case• Homework

REMINDERS:• Quiz – tomorrow after lesson• Wednesday/Thursday: Group

presentations• Thursday: Unit Review • Friday: Unit Test---bring other

work to do in case you get finished early!!

Minds ON

• http://www.bing.com/videos/watch/video/cool-facts-about-genetics/1aih9s3qn

Correlative relationship vs. Causal relationship: discuss….

Success Criteria

Last Week’s Learning Goals are posted. What are some of the things we need to know about or how to do in order to be successful on a quiz or to know that we have had a full understanding of the material?

Friday’s Recap

Types of Dominance:• Complete Dominance: Occurs when a dominant trait completely

masks the recessive allele. • Incomplete Dominance: Occurs when neither gene is dominant or

recessive; the gene effect is mixed; we use 2 different letters for the homologous pair since neither is dominant.• Co-Dominance: Occurs when neither gene is dominant or recessive;

gene effects are NOT mixed; therefore, both genes are expressed at the same time!

Friday’s Recap:

Complete Dominance Incomplete Dominance Co-Dominance

Friday’s Recap:

Complete Dominance Incomplete Dominance Co Dominance

Autosomal TraitsWe have been looking at autosomal traits so far:• Refers to a trait passed on

through the autosomal (non-sex) chromosomes• Autosomal dominant: One or two

copies of the trait was passed from one or both parents to cause the trait to appear• Autosomal recessive: Two copies

of the recessive trait must be passed on from both the parents in order for it to appear

Predicting Gender

• Two sex chromosomes determine gender:

X and Y

• Female Genotype: XX• Male Genotype: XY

Predict the probability of a couple having a boy using a Punnett Square

Predicting Gender

50% chance of a boy50% chance of a girl

X-Linked Traits

• All genes found on the ‘X’ chromosome are “linked”.• Many of the genes on the ‘X’ are

not on the ‘Y’.• The ‘X’ is larger and has many

genes that are not related to gender… • (i.e. colour vision, blood clotting

etc.)

Are You Colour Blind?

Can you see something in the dots?

X-Linked Traits

• Refers to a trait that is passed on through the X (female sex)chromosome • If a recessive gene is on the ‘X’:- In males it will always be expressed since there is no homologous pair on the ‘Y’.- Therefore (sorry guys) recessive, X-linked diseases are much more common in males!

An Example of an X-Linked DisorderHemophilia: Inability to Stop Bleeding

Since gender and the gene are important, both must be noted.

Dominant allele – HRecessive allele – h – dominant gene on ‘X’– recessive gene on ‘X’Y – no gene on the ‘Y’

Hemophilia

• Female genotypes – Normal– Normal but a ‘Carrier’– Hemophiliac (very rare)• Male genotypesY– NormalY- Hemophiliac• Predict the offspring using a Punnett Square for: Mother carrier and a normal father

Hemophilia

Y

Y

Mom:Dad:Y

𝑋𝐻

𝑋 h

𝑋𝐻 Y

Pedigrees

• Presentation of family information that is easy to read; can show genetic patterns of disease

• Circles = females; Squares = males; Diamond = unknown gender

• Deceased = diagonal line through• Unaffected = Clear/white; Affected = filled

in/black; Carrier = shaded• Marriage = Individuals attached side by

side• Children = Vertical line down • Siblings = Individuals coming down off

shared horizontal line

Seeing Genetic Patterns of Disease Using a Pedigree Chart

• Autosomal Disorders are disorders that are passed through the non-sex chromosomes (autosomes)• Autosomal Dominant: If a disease is autosomal dominant, it means you only

need to get the abnormal gene from one parent in order for you to inherit the disease. One of the parents may often have the disease • Autosomal Recessive: An autosomal recessive disorder means two copies of

an abnormal gene must be present in order for the disease or trait to develop

• X/Y-Linked Disorders are disorders that are passed through sex chromosomes (X / Y chromosomes)

PedigreesAutosomal Dominant Pedigree Autosomal Recessive PedigreeX-Linked Pedigree

An Example of X-Linked Traits Using a Pedigrees

• Muscular Dystrophy is a disease that causes weakening of the muscular-skeletal system, inhibiting those affected from locomotion. There are many forms of this disease.

• The Duchenne form of this disease is caused by a mutation on the X chromosome. It is an X-linked recessive disorder. It is more severe than the Becker form of the disease.

• This means that substantially more boys than girls are going to be affected by this disease

Muscular Dystrophy Pedigree

Try it…

Sally and Brian got married and had 3 daughters, Brianna, Roxanne and Racheal. Sally learned that she is a carrier of Duchenne muscular dystrophy. Brianna got married to Mike and had two sons, Will and Ryan. Mike appears to be healthy; however Will has muscular dystrophy but Ryan does not. Draw a pedigree.

Muscular Dystrophy Pedigree

A Case of Mistaken Maternity

We will read the first part together, then in groups work on it together. We will take it up.

Homework

• Pedigree Charts• Hemophilia sheet • Mistaken Maternity sheets• Any other sheets we have done