Module 10 human heredity
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Transcript of Module 10 human heredity
Human Heredity
Chromosomes
• Every human cell has 46 chromosomes (23 pairs of chromosomes)
• A karyotype is a picture of the 23 pairs of chromosomes.
Examples of Karyotypes
Autosomes are the first 22 pairs of chromosomes (#1-#22)
Sex Chromosomes determine the sex and are pair #23
XX-female
XY-male
Female (XX)
Male (XY)
•Muskopf, Shannan. Online Images. The Biology Corner. 8 May 2007. http://www.biologycorner.com/bio1/celldivision-chromosomes.html
Pedigree Charts-shows genetic history of a family over many generations
•Muskopf, Shannan. Online Images. The Biology Corner. 8 May 2007. http://www.biologycorner.com/bio2/humangenetics.html
Generation I
Generation II
Generation III
Symbols in a Pedigree Chart
• Female
• Male
• Married Couple– horizontal line connects a
married couple
• Siblings
• Shaded: individual has the trait
• Not shaded: does not have the trait
• Half-shaded: carries the trait (heterozygous)
Pedigree Chart of a Dominant Trait• Huntingtons disease is a dominant disease that damages the
nervous system• One dominant allele means you get the disease • HH (homozygous) and Hh (heterozygous) will have the disease• hh (homozygous) will not have the disease• One parent has to have it to pass on to child
What is the genotype of the father?
What is the genotype of the son?
Pedigree Chart of a Dominant Trait
The father does not have the dominant disease so he must have 2 recessive alleles; his genotype is hh
The son has the dominant disease so he has to have at least one dominant allele. Is his genotype HH or Hh? One allele came from his father so his genotype is Hh.
Pedigree Chart of a Dominant Trait
hh HH
Hh
What are the chances that future offspring of this couple will have this dominant disease? Use the genotypes of the parents to draw a punnett square.
Pedigree Chart of a Dominant Trait
hh HH
Hh
All of the offspring have the dominant allele so 100% of their future children will have this dominant disease.
H H
h Hh Hh
h Hh Hh
Pedigree Chart of a Recessive Trait• Cystic fibrosis is a recessive disease causing digestive problems• HH (homozygous) and Hh (heterozygous) will NOT have the disease• hh (homozygous) will have the disease• Must inherit recessive allele from each parent to have the disease
What is the genotype of the father?
What is the genotype of the daughter?
Pedigree Chart of a Recessive Trait
She must have 2 recessive alleles to have this disease. Her genotype is cc.
The dad does not have this recessive disease so his genotype is either CC or Cc. Since he passed on one recessive allele to his daughter, his genotype is Cc.
Pedigree Chart of a Recessive Trait
What are the chances that future offspring of this couple will have this recessive disease? Use the genotypes of the parents to draw a punnett square.
Cc Cc
cc
Pedigree Chart of a Recessive Trait
Cc Cc
cc
C c
C CC Cc
c Cc cc
Only 1 out of 4 offspring have the recessive disease (cc). There is a 25% chance of future offspring having the disease.
Sex-Linked Traits (X-linked)
• Sex-linked genes are located on the sex chromosomes (23rd pair) and deal with the X and Y chromosome
• A female is XX; a male is XY• Sex-linked genes are shown as superscripts on
the X chromosome
Sex-Linked Traits in females
• If a disorder is caused by a recessive gene, a female’s genotype could be XBXB or XBXb and she will not have the disorder. The XBXb female would be a carrier.
• A female with a sex linked disorder would be written as XbXb because she must have both recessive alleles.
Sex-Linked Traits in males
• The Y chromosome does NOT carry a gene. A male without the recessive sex-linked disorder would be XBY. A male with the sex-linked disorder would be XbY.
• Sex-linked disorders are more common in males because males only need 1 copy of the recessive allele since they have only 1 X chromosome. Females must have 2 copies of the recessive allele since they have 2 X chromosomes.
• Common sex-linked disorders include color blindness and hemophilia (a bleeding disorder)
Sex-linked pedigree for color blindness
What is this male’s genotype?
Colorblindness is a recessive sex-linked disorder
This is a male so his sex chromosome is XY
The square is shaded so this male is colorblind
His genotype is XbY (Remember, there are no superscripts on the Y chromosome)
•Muskopf, Shannan. Online Images. The Biology Corner. 8 May 2007. http://www.biologycorner.com/bio4/notes/inheritance3.html
Sex-linked pedigree for color blindness
What is this male’s genotype?
This is a male so his sex chromosome is XY
The square is not shaded so this male has normal vision
His genotype is XBY
•Muskopf, Shannan. Online Images. The Biology Corner. 8 May 2007. http://www.biologycorner.com/bio4/notes/inheritance3.html
Sex-linked pedigree for color blindness
What is this female’s genotype?
This is a female so her sex chromosome is XX
This female is not colorblind so her genotype is either XBXB or XBXb
Her son is shaded so he is colorblind (XbY) and inherited the Y chromosome from his father and the Xb chromosome from his mother.
The mother has to have a Xb in her genotype
Her genotype is XBXb•Muskopf, Shannan. Online Images. The Biology Corner. 8 May 2007. http://www.biologycorner.com/bio4/notes/inheritance3.html
What percentages can be expected in the offspring of a cross between a female carrier for color blindness and a male with a normal color vision? Show your work with a punnett square.
Practice
What percentages can be expected in the offspring of a cross between a female carrier for color blindness and a male with a normal color vision? Color blindness is a recessive trait attached to the X chromosome. A female carrier means heterozygous.
female carrier XBXb
male with normal vision XBY
Practice
XB Xb
Y XBY XbY
XB XBXB XBXb
25% colorblind males
25% carrier females
25% normal males
25% normal females
• Karyotypes are used to determine if an offspring has the right number of chromosomes (46 in humans)
• Down Syndrome – 47 chromosomes because there are 3 copies of
chromosome #21– Causes mental retardation
3 copies of #21
•Muskopf, Shannan. Online Images. The Biology Corner. 8 May 2007. http://www.biologycorner.com/bio1/celldivision-chromosomes.html
• Amniocentesis-during pregnancy, a small amount of fluid from the sac surrounding the embryo is used to make a karyotype to determine if the fetus has the correct number of chromosomes
Diagnosis of Chromosomal Abnormality