Download Sex Chromosomes

Ch 14 Section 1 & 2 Human Heredity
Human Chromosomes
• _______________________________ – an organism’s full set of genetic info.
• _______________________________ – picture of a complete set of chromosomes
arranged in order of decreasing size
– Homologous chromosomes arranged in pairs
– Shows ________________ and ______________________ of chromosomes
Sex Determination
• Sex Chromosomes – determines _____________________; __________________
– X chromosome contains _______________ genes
– Y chromosome contains _______________ genes
• __________________________ – any chromosome that is NOT a sex chromosome
• Normal Humans have ______________ chromosomes:
– 44 autosomes and 2 sex chromosomes
– Female has ____________ and Male has ________________
Sex Determination Problem
• What is the probability of a man and woman having a baby girl?
Sex-Linked Inheritance
• Sex-Linked Gene – gene located on _________________ chromosome
• Sex-Linked Traits – characteristic controlled by genes on the X or Y chromosome
– X Linked  traits found on the __________ chromosome;
expressed in ______________________________
– Y-Linked  traits found on the ___________ chromosome;
expressed only in ___________________; passed from father to son
Dominant X-Linked Traits
• Trait is expressed in females & males, if they have 1 copy of dominant allele.
– Male  XAY
– Female  XAXA or XAXa
• Trait is NOT expressed if male has 1 copy of the recessive allele and female has 2
copies of the recessive allele.
– Male  XaY
– Female  XaXa
Recessive X-Linked Traits
• Trait is expressed only in females that have 2 copies of the recessive allele.
– Female  XaXa
• Trait is expressed only if males have 1 copy of the recessive allele
– Male  XaY
Sex-Linked Trait Practice
 Circle those affected by a dominant X-linked trait.
XBXb XcY XdXd XRXR XNY
 Circle those affected by a recessive X-linked trait.
XaXa XLY XTXt XZXZ XpY
Sex-Linked Trait Practice
• The trait for red-green colorblindness is a recessive X-linked trait. The mother is a
carrier for colorblindness and the father is not color blind, what is the probability
that they will have a child that will be color blind?
• Hemophilia is a recessive X-linked disorder of the blood. Two normal parents have
a son that has hemophilia, what is the probability that they will have a daughter
that has hemophilia?
• Hairy ears is inherited as a Y-linked trait. A man with hairy ears marries a woman
with normal ears. What is the probability that they will have a female child with
hairy ears? Male child with hairy ears?
• This disease is inherited as an X sex-linked dominant disease. An affected male
marries a homozygous recessive female. What is the probability that they will
have an affected daughter? Affected son?
Changes in DNA = Changes in Phenotype
• Changes in a gene’s DNA sequence can change proteins by altering their amino
acid sequences, which may directly affect one’s phenotype.
• Genetic disorders caused by changes in genes  changes ____________________
Recessive Genetic Disorders
• A _______________________________ allele codes for a faulty protein.
• __________________ – an individual that is heterozygous for a recessive disorder.
– 50% chance of passing recessive allele to child
– __________  no disorder
– __________  no disorder but a carrier for it
– __________  disorder
Dominant Genetic Disorders
• A _______________________________ allele codes for a faulty protein.
– Only one parent needs to have one copy of the defective allele in their
gametes to pass the disorder to their children.
– ________________________  disorder
– ______________  no disorder
Males
Squares
Females
Circles
Expresses Trait
Filled
No Trait
Unfilled
Carrier for Trait
Partially Filled
Roman Numerals
Generations (P1, F1, F2)
Numbers
Birth order of offspring
Pedigree
• ______________________________ – chart that shows traits, diseases, or
disorders within a family across several generations.
– Used to infer genotypes by observing phenotypes.
– Tracks dominant, recessive, and sex-linked traits.
– _______________________________ traits easier to recognize.
– Accurate records of family history  predict effects in future offspring.
Nondisjunction
• __________________________________ – homologous chromosomes fail to
separate properly during meiosis cells having abnormal number of
chromosomes  chromosomal disorders.
– Normal = ___________
– Any number other than 46 = Abnormal
• Only 1 chromosome copy = _____________________________
• 3 chromosomes of one type = _______________________________
– Nondisjunction = serious disorders  often fatal
Down Syndrome
• Also called _________________________________
• Nondisjunction of chromosome #21
• Symptoms: distinct facial features, mental retardation, short stature, heart
defects.
• Affects 1/800
• Frequency increases with mother’s age.
Nondisjunction
• Can occur with autosomes and sex chromosomes.
– _________________________________ – female is missing X chromosome
– _________________________________ – female with 3 X chromosomes
– _________________________________ – male with XXY
– ___________________________ – male just receives Y chromosome & no X
Fetal Testing
• Tests that provide genetic information on developing fetus.
• _________________________  diagnosing chromosomal abnormalities early
• _________________________  miscarriage & infection