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Inheritance Patterns and Human Genetics
Sex Chromosomes and Autosomes
• Sex Chromosomes contain genes that determine the gender of an individual.
• Many organisms have the XX & XY chromosomal mechanism to determine the sex of an individual.
Sex Chromosomes and Autosomes
• In certain organisms, like chickens and moths, males have two identical chromosomes and females have two different chromosomes.
Sex Determination
• In mammals, the male determines the sex of the offspring.
• If the sperm contributes an X sex chromosome, a female will be created
• If the sperm contributes a Y sex chromosome, a male will be created.
The Y Chromosome
• In a male mammal, the Y chromosome contains a gene called SRY (Sex-determining Region Y)
• This gene codes for a protein that causes gonads of an embryo to develop as testes.
Sex Linkage
• Genes found on the X chromosome are said to be X-linked
• Genes found on the Y chromosome are said to be y-linked
Mutations
• Change in the nucleotide-base sequence of a gene or DNA molecule
Mutations
• Germ-cell mutations occur in an organism’s gametes.
• These do not affect the organism itself, but can be passed on to offspring.
Mutations
• Somatic-cell mutations take place in an organism’s body cells.
• These mutations can affect the organism but are not passed on to offspring
Mutations
• Lethal mutations cause death, often before birth.
• Some mutations will produce a phenotype that is beneficial to an organism.
• Mutations provide the variation upon which natural selection acts.
Chromosome MutationDeletion
• Loss of a piece of a chromosome due to breakage
Chromosome MutationInversion
• A chromosomal segment breaks off, flips around backward, and reattaches.
Chromosome Mutation Translocation
• A piece of one chromosome breaks off and reattaches to a nonhomologous chromosome
Chromosome MutationNondisjunction
• A chromosome fails to separate from its homologue during meiosis.
Gene Mutations
• The substitution, addition, or removal of a single nucleotide is called a Point Mutation
• This image shows a substitution point mutation.
Gene Mutation (Frameshift)
• If a nucleotide is deleted (Deletion), this can cause an incorrect grouping of the remaining codons. This is called a frameshift mutation.
Gene Mutation (Frameshift)• If a nucleotide is inserted (insertion mutation), this
can cause an incorrect grouping of the remaining codons. This is also called a frameshift mutation.
CTTCGAAGTC CTATCGAAGTC
Inheritance of TraitsPedigrees
• A diagram that shows how a trait is inherited over several generations.
Can you make sense of this Pedigree?
Polygenic Inheritance
• Most human traits are polygenic.
• This means they are influenced by several genes.
• Often show many degrees of variation.
• Eye color, height, hair color and skin color.
Multiple Allele Inheritance
• Genes with three or more alleles
• The ABO blood types are controlled by 3 alleles.
• A, B, i• A & B are dominant to i
Blood Types
Phenotypes Genotypes
A AA, Ai
B BB, Bi
AB AB
O ii
Rh Factor for Blood
• Rh stands for Rhesus Factor
• If you are Rh +, you have a blood protein that Rh – people do not have.
• Rh+ is dominant to Rh –
• 85% of the US population is Rh+
Rh Factor Problems
• When a pregnant woman who is Rh - is having a Rh + baby the woman will produce antibodies against the foreign protein.
Rh Factor Problems
• The woman’s first child will not be affected.
• If the woman has any other children, her antibodies can attack the babies blood causing death to the baby.
• There are injections that are given to women today to keep this from being a problem.
X – Linked Traits
• Traits and disorders that are found on the X chromosome
• For a man to have an X-linked disorder, he only needs the trait on his one X.
• For a female to have an X-linked disorder, she needs to have the trait on both of them. (unless it is a dominant X-linked trait)
X – Linked Traits
• Color blindness is a recessive X-linked disorder
X – Linked Traits
• Hemophilia is also a recessive X-linked disorder
Sex-Influenced Traits
• The presence of male or female sex hormones influence the expression of certain human traits
Disorders due to Nondisjunction
• Monosomy – when an organism has only one copy of a particular chromosome
• Trisomy – when an organism has 3 copies of a particular chromosome
Disorders due to Nondisjunction
• Down Syndrome (trisomy 21)
• Turner Syndrome (X0)
• Klinefelter’s Syndrome (XXY)
• Triple X Syndrome (XXX)
Genetic Screening
• Amniocentesis – amniotic fluid is removed and a karyotype of the baby is produced.
Genetic Screening
• Chorionic Villi Sampling – a sample of the tissue that grows between the mother’s uterus and the placenta is taken.
• A karyotype is produced.