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 Mutation Deletion Loss of a piece of a chromosome due to breakage

Chromosome Mutation Inversion 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 Mutation Nondisjunction 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 Traits Pedigrees 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 PhenotypesGenotypes A AA, Ai B BB, Bi ABAB Oii

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.