sex-linked traittraits carried by genes located on the X or Y sex chromosomes

genetically normal females: XX

genetically normal males: XY

Glossary

sex-linked trait• most X-linked characteristics are recessive

in females

• which means that unless they are present on both X chromosomes of a female, the trait is carried but not expressed

Glossary

•males, with only one X chromosome, more commonly exhibit such traits phenotypically

•e.g. hemophilia

•e.g. red-green color blindness

sex-linked trait

Glossary

Diana

Sex-linked Punnet SquareXX x XY

X Y

X

X

Sex-linked Punnet SquareXX x XY

X Y

X X X

X

Sex-linked Punnet SquareXX x XY

X Y

X X X

X X X

Sex-linked Punnet SquareXX x XY

X Y

X X X X

X X X

Sex-linked Punnet SquareXX x XY

X Y

X X X X

X X X X

Sex-linked Punnet SquareXX x XY

X Y

X X X X Y

X X X X

Sex-linked Punnet SquareXX x XY

X Y

X X X X Y

X X X X Y

Sex-linked Punnet Square:Hemophilia carrier

XHXh x XHY

X Y

X

X

Sex-linked Punnet Square:Hemophilia carrier

XHXh x XHY

XH Y

XH

Xh

Sex-linked Punnet Square:Hemophilia carrier

XHXh x XHY

XH Y

XH XH XH XH Y

Xh

Sex-linked Punnet Square:Hemophilia carrier

XHXh x XHY

XH Y

XH XH XH XH Y

Xh XH Xh Xh Y

Sex-linked Punnet Square:Hemophilia carrier

XHXh x XHY

XH Y

XH XH XH XH Y

Xh XH Xh Xh Y

Hemophilia!

Human Geneticsand Meiosis

The study of inheritance patterns in humans

Oculocutaneous albinism

http://www.foxnews.com/slideshow/health/2009/10/19/celebrities-different-color-eyes/#slide=1

What each of the human chromosomes look like

Karyotype: A photomicrograph of chromosomes arranged according to a standard classification

In other words…

• Chromosomes are digitally arranged so that they are matched with their homologue or “partner” chromosome.

• Homologue chromosomes are the same size, shape, and carry the same genes, and one is inherited from each parent.

• They are numbered according to size.

Sex determination with karyotype

• This karyotype has 23 exact pairs, which means the person is female.

• Note that #23 chromosomes are both X.

Normal human male

• Note that #23 chromosomes are X and Y.

Is this person female or male?

Trisomy 21

• Abnormality shown in karyotype

• Note that there are three copies of #21 chromosome.

• This person has Down Syndrome.

Photos of Down Syndrome patients from the National Down Syndrome Society

Correlation between mother’s age and Trisomy 21 incidence

Monosomy X

• Abnormality shown in karyotype

• Note this person only has 1 copy of the X chromosome.

• This female has Turner’s syndrome.

XXY Male (Extra X)

How are DNA samples obtained for karyotypes?

Amniocentesis: obtaining amniotic fluid which has cells from the fetus

Chorionic villi sampling: removing cells from the chorion with fetal tissue

If there are chromosomal number abnormalities, how do they form?• Meiosis: the process of creating sperm or

egg from a diploid cell

• If there is a mistake when chromosomes are separating, then the resulting sperm or egg will have too many or too few chromosomes.

How can siblings look alike but not exactly the same if they come from the same parents?

Crossing over

• The chromosomes during prophase I undergo crossing over, where parts of the homologues randomly switch places.

Importance of crossing over

• The gene combinations that a person gets from his or her parents will be different, to varying degrees, than the combination a sibling may get.

More sibling similarities

What other chromosomal disorders can arise?

• Deletion• Inversion• Translocation*• Duplication

*Don’t worry about this one.

Chromosomal mutations

Deletion

Duplication

Inversion

Translocation

Problems with chromosomes

• Duplication: copied parts of chromosome

A

B

C

D

A

B

B

B

C

D

Problems with chromosomes

• Deletion: missing parts of chromosome

A

B

C

D

A

D

Problems with chromosomes

• Inversion: parts of chromosome tched

A

B

C

D

A

C

B

D

Human genetic disorders from deleterious genes

• Sometimes the alleles inherited contribute to disorders and not from the number or shape of the chromosomes.

1. Sex-linked: genes found on X or Y chromosome

2. Recessive: requires 2 allele copies to express disorder

3. Dominant: requires only 1 allele copy to express disorder

Recessive disorders

Dominant disorder

Are you red-green color blind?

• Yes, if you have a difficult time distinguishing a number from this picture

Pedigrees: a chart which can show trait inheritance through several generations

Albinism

Symbols

Male Female

marriage

More symbols

She gave birth!

Even more symbols

4 offspring

Still more symbols

Affected. AA or aa

Normal heterozygous

Albinism – recessive disorder

aa Aa

Aa aa Aa Aa

Deafness – dominant disorder

Aa or AA?

Aa Aa Aa Aa

aa

Mother must be AA.

Colored blindness – Sex linked

XCXc

XcY XCXc XCY XcXc

XcY