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.