DQ: Compare and contrast the two pictures. How are they similar? Different? What type of information might you be able to gather from them?

Objectives…

Describe a karyotype and it’s uses.

Define sex-linked genes and explain how sex-linked disorders affect males and females.

Define “pedigree” and analyze one.

• What is the difference between autosomes and sex chromosomes?

– Sex Chromosomes : Determine an organism’s sex

–Males : XY Females : XX

–Autosomes : All other chromosomes in a cell

• Males and females are born in a 50:50 ratio because of the way in which sex chromosomes

X

X

X Y

XX

XX

XY

XY

• How many chromosomes are in a human body cell?

– 46

• How many of those are sex chromosomes?

– 2

• How many does that leave for autosomes?

– 44

• To analyze chromosomes, cell biologists look at karyotypes.

• Look at the picture to the right… What is the purpose of a karyotype?

• What’s the purpose of a karyotype?

– Determine the sex of an organism

– Look for any chromosomal abnormalities

• Why are there two chromosomes together?

– Homologous Pairs! (Remember those things?)

• Chemicals stain the DNA causing the light and dark bands

– Helpful for pairing the correct chromosomes

– Each band contains hundreds of different genes

• Arranged largest to smallest

• Genes located on sex chromosomes are said to be sex-linked genes.

• Most sex-linked genes are found on the X chromosome

• Who do you think is more likely to be affected by sex-linked disorders?

– MALES because they only have one X chromosome

• Three human genes associated with colorblindness are on the X chromosome

• 1 in 10 males in the U.S. have red-green colorblindness

Red-Green Colorblindness

ARE YOU COLORBLIND?

XC

X

X Y

XC = Colorblind X = Normal

XCX

XX

XCY

XY

• What is a karyotype? What are it’s uses?

– Picture of all of the chromosomes in a cell; used to determine sex and/or abnormalities

• What is the difference between an autosome and sex chromosome?

– Sex chromosome determines gender; autosomes are all other chromosomes

• Why are men more likely to be affected by sex-linked disorders?

– They only have one X; nothing to mask the trait

• Pedigree charts show the relationships and inheritance of traits between family members

• Genetic counselors use pedigrees to infer the genotypes of family members

• Fill in the labels missing in your pedigree “key”

• How might you identify a pedigree as autosomal or sex-linked?

–Autosomal : Approximately an even amount of males and females affected

– Sex-Linked : Usually only males are affected; females are carriers

You Decide…

• Are the following pedigrees showing autosomal or sex-linked inheritance?

You Decide…

• Are the following pedigrees showing autosomal or sex-linked inheritance?

You Decide…

• Are the following pedigrees showing autosomal or sex-linked inheritance?

• What is the difference between a karyotype and pedigree? – Karyotype shows pictures of your actual

chromosomes; pedigree shows family history and pattern of inheritance

• What is the difference between a pedigree and a punnett square? – A Punnett square allows you to calculate the

expected results of a cross; pedigree shows the pattern of inheritance of a family trait

• Can You…

Describe a karyotype and it’s uses?

Define sex-linked genes and explain how sex-linked disorders affect males and females?

Define “pedigree” and analyze one?