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?
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