SEX LINKED TRAITS & PEDIGREE CHARTS

April 7, 2011

THIS WEEK.. Monday: Incomplete & Co-dominance Tuesday: Quest Wednesday: multiple alleles &

polygenic inheritance Thursday: sex-linked traits & pedigree

charts Friday: PD Day.

REVIEW Incomplete Dominance: A condition in which

neither allele for a gene completely conceals the presence of the other

Co-dominance: The condition in which both alleles for a trait are equally expressed in a heterozygote: both alleles are dominant

Multiple alleles: Many traits in humans result from the interaction of more than two alleles for one gene

Polygenic inheritance: A trait that is controlled by more than one gene

REVIEW Chromosomal Theory of

inheritance: Chromosomes carry

genes, the units of heredity

Pair chromosomes segregate during meiosis (each egg or sperm cell has ½ the number of chromosomes as found in the somatic/body cells)

SEX-LINKED INHERITANCE Thomas Hunt Morgan (1866-

1945): studied fruit flies Reproduce rapidly Have a large number of offspring Males can be easily

distinguished from Females

Discovered that white-eye mutations only appeared in males

SEX-LINKED INHERITANCE A trait controlled by genes on the X or

Y chromosome These traits show different rates of

appearance between males and females

For fruit flies, the eye colour trait is not carried on the Y chromosome, only the X

SEX-LINKED INHERITANCE Colour blindness:

X-linked recessive, occurs more in males

Hemophilia: A condition that affects

the body’s ability to produce proteins involved in blood clotting

SEX-LINKED INHERITANCE Recessive lethal: a trait that, when both

recessive alleles are present, results in death or severe malformation of the offspring. Occurs more frequently in males

SEX-LINKED INHERITANCE Barr Body: (Dr. Murray Barr, UWO)

one of the X chromosomes in females randomly becomes inactive in each cell

Which X chromosome is inactivated is random, some cells may have different X chromosomes & genes expressed.

SEX-LINKED INHERITANCE Anhidrotic ectodermal dysplasia:

patches of skin contain sweat glands and some patches don’t, depending on which X chromosome is active in the cell Cannot control body temperature properly.

PEDIGREE CHARTS A graphic presentation of a family tree

that permits patters of inheritance to be followed for a single gene

HOMEWORK Read pg 141-142, 163-167 Genetics worksheet 4 & pedigree

examples Create your own pedigree chart

representing a trait in your family. must have at least 3 generations Include “key”