Chap 4 Evolutionary Theory and Predetermined Behavior

Evolutionary Theory and Predetermined Behavior

Charles Darwin

• Studied Natural Selection and evolution

What does Natural Selection and evolution consist of

• High reproductive capacity

• Natural selection (adaptive advantage)

• Variability

Natural selection

The process by which inherited traits that provide a selective advantage (increased probability of survival) come to be more prevalent in a population.

FRANCIS GALTON

• Studied Eugenetics

• Human traits of intelligence or ability, could be improved by controlling reproduction.

What did Galton believe?

that encouraging people with "desirable" traits to have more children, while discouraging those with "undesirable" traits from having children, could improve the human race.

Mendelian Genetics

• Gregor Mendel: studied of how traits are inherited from one generation to the next

Three principles of Mendelian Genetics

The principle of Segregation

The principle of Dominance

The principle of Independent Assortment

The principle of Segregation

• traits are inherited as discrete units (now known as genes), and each parent contributes one unit to their offspring

The principle of Dominance

• some traits are dominant and mask the presence of recessive traits in the offspring.

The principle of Independent Assortment

• different traits are inherited independently of each other, meaning the inheritance of one trait does not affect the inheritance of another.

WALTER SUTTON (1902) & THEODOR BOVERI

CHROMOSOMAL THEORY OF INHERITANCE:

• Theodor Boveri (early 1900s) showed that chromosomes play a key role in inheritance and that each chromosome carries important genetic information.

• Walter Sutton (also early 1900s) worked on the same idea and proposed the chromosome theory of inheritance, which suggests that genes are located on chromosomes and are passed down during reproduction.

MORGAN (1910)

• Studied relationship between genes and chromosomes,

• Fruit Fly (Drosophila melanogaster)

CHROMOSOMAL THEORY OF INHERITANCE

• Fundamental principle in genetics that explains how genes are transmitted from parents to offspring through chromosomes

Development of the CHROMOSOMAL THEORY OF INHERITANCE

• Origins: The theory was developed in the early 1900s by scientists Theodor Boveri and Walter Sutton.

• They observed that chromosomes behaved in ways that matched Mendel's laws of inheritance.

• Key Observations: Boveri and Sutton noted that chromosomes segregate & assort independently during meiosis, the process of cell division that produces gametes (sperm and eggs).

Core principles of CHROMOSOMAL THEORY OF INHERITANCE

• Chromosomes Carry Genes: Genes are located on chromosomes, which are the carriers of genetic information.

• Segregation: During meiosis, chromosomes (and thus genes) segregate so that each gamete receives only one chromosome from each pair.

• Independent Assortment: The way chromosomes are distributed to gametes is random, leading to genetic variation.

Supporting evidence to Chromosomal Theory of Inheritance.

• Fruit Fly Experiments

• Genetic Linkage and Recombination

Genetic Linkage and Recombination

Morgan also discovered that genes located close together on the same chromosome tend to be inherited together, a phenomenon known as linkage

Fruit Fly Experiments

• Thomas Hunt Morgan's work with fruit flies (Drosophila melanogaster) provided strong evidence for the Chromosomal Theory of Inheritance.

• He demonstrated that specific traits were linked to specific chromosomes.

Non-Mendelian Inheritance

• Multiple Alleles: More than one allele for a trait.

• Incomplete Dominance: A dominant gene is not fully expressed (e.g., Intermediate Inheritance).

• Intermediate Inheritance: Intermediate phenotype.

• Codominance: There is codominance between two alleles

• Sex-linked inheritance: XX or XY.

• ABO System and Rh System Inheritance: A and B alleles (codominant) and 0 (recessive)

Multiple Alleles: More than one allele for a trait.

• Definition: More than two alleles exist for a particular gene within a population.

• Example: The ABO blood group system, where the gene for blood type has three alleles: A, B, and O.

Incomplete Dominance: A dominant gene is not fully expressed (e.g., Intermediate Inheritance).

• Definition: A situation where the dominant allele does not completely mask the effects of the recessive allele in heterozygotes.

• Example: Flower color in snapdragons, where crossing red and white flowers results in pink offspring

Intermediate Inheritance: Intermediate phenotype.

• Definition: The phenotype of heterozygotes is intermediate between those of the two homozygotes.

• Example: Similar to incomplete dominance, where the resulting phenotype is a blend of the two parental traits

Codominance: There is codominance between two alleles

• Definition: Both alleles in a heterozygote are fully expressed, resulting in a phenotype that shows both traits simultaneously.

• Example: The ABO blood group system, where individuals with genotype AB express both A and B antigens

Sex-linked inheritance: XX or XY.

Definition: Traits that are associated with genes located on the sex chromosomes (X and Y).

Example: Hemophilia and color blindness, which are often linked to the X chromosome. Various traits linked to the X and Y chromosomes, which are usually transmitted by recessive inheritance. More common in males.

ABO System and Rh System Inheritance: A and B alleles (codominant) and 0 (recessive)

• ABO System: Involves three alleles (A, B, and O). A and B are co-dominant, while O is recessive.

• Rh System: Involves the presence (+) or absence (-) of the Rh antigen. The Rh+ allele is dominant over Rh-

Alteration in the number of chromosomes

• Trisomy (3 chromosomes), the lack of one chromosome can only be in one sex chromosome (Turner syndrome, XO).

Structural alterations of chromosomes

• deletion

• inversion

• translocation

deletion

a chromosome fragment is missing

inversion

a piece of chromosome is joined to another in an inverted position

translocation

it is exchanged for another segment of a nearby chromosome

Autosomal inheritance (not sex-linked)

inherited equally in males and females.

Lethal genes

cause the death of the individual before sexual maturity

• either Gametic

• or Zygotic

• Gametic

they act in the gametes producing their death

• Zygotic

they act from the formation of the zygote until it reaches sexual maturity

According to lethal genes dominance

• dominant

• recessive

 According to lethal genes action

• complete lethal

• semi-lethal

• sublethal

complete lethal of lethal genes action

causing death in 90% of cases

semi-lethal of lethal genes action

causing death 50-90% of cases

sublethal of lethal genes action

causing death 10%

Chromosome nr 23

linked to sex

chromosomes 1-22

Autosomal inheritance

Autosomal dominant transmission

Single Allele

Equal Gender Distribution

Generational Presence/Vertical inheritance

Single Allele

Only one copy of the dominant allele is needed for the trait to be expressed.

Equal Gender Distribution

• Both males and females are equally likely to inherit and express the trait since autosomes are not sex-linked.

Generational Presence/Vertical inheritance

• Traits typically appear in every generation, as affected individuals have a 50% chance of passing the dominant allele to their offspring.

Autosomal recessive transmission

• Two Alleles

• Carrier Status

• Equal Gender Distribution

• Generational Patterns

Two Alleles

• An individual must inherit two copies of the recessive allele (one from each parent) to express the trait

Carrier Status

• Individuals with only one copy of the recessive allele are carriers and do not exhibit the trait but can pass the allele to their offspring.

Equal Gender Distribution

Both males and females are equally likely to inherit and express the trait since autosomes are not sex-linked.

Generational Patterns

• Traits may skip generations if carriers do not express the trait.

• Increased risk in consanguineous unions

Sexual chromosomes

• Human 23 pairs (46 chromosomes)

• 22 pairs of chromosomes

• 1 pair of Sexual Chromosomes

Diploid

• refers to a cell or organism that has two complete sets of chromosomes, one set inherited from each parent.

In humans, for example, most cells are diploid and have 46 chromosomes (23 pairs)

haploid

Cells (like sperm and egg cells), which have only one set of chromosomes.

• opposite of diploid

Sex-linked inheritance diseases

DALTONISM

HEMOPHILIA

• most common in men

why does sex-linked inheritance occur?

• If a gene for a sex-linked trait is defective or recessive and located on the X chromosome, men are more likely to express the trait because they only have one X chromosome.

• If that single X carries the defective gene, there is no second X to "mask" the effect.

BLOOD GROUPING 

There are 4 essential antigens that define the 4 blood groups known by the acronyms:

• 0, A, B and AB

Rh System (Rhesus Factor)

Protein responsible for the incompatibility of some blood groups.

BLOOD GROUPING AND RH SYSTEM

• We all have these two components: ABO + RH (They are two different Protein Families).

• BLOOD GROUPS MATCH WITH THE

  PRESENCE OF CERTAIN PROTEINS.

  THE BLOOD GROUPS CAN BE:

  A

  B

  O

  AB

Neurotransmitters

• complex behavioural effects and variations based on different factors

• (drugs, psychotropic drugs, enzymatic changes, genetic variations)

• Serotonin

• Dopamine

Serotonin

• 5HT1B receptors associated with reduced aggression.

Mice lacking these receptors showed higher levels of aggressiveness, as well as humans with lower activation due to low levels of 5-HT.

• 5HT1A receptor inactivity associated with anxiety in adulthood (critical period).

5HT1A

receptor inactivity associated with anxiety in adulthood (critical period).

5HT1B

receptors associated with reduced aggression.

Dopamine

• Gene-neurotransmitter relationship for Parkinson's disease.

• Alterations in D4 receptor associated with increased novelty and sensation seeking (less behavioral inhibition).

• Both the DAT1 transporter and the DR4D receptor have been associated with ADHD (Motor and attentional in different brain pathways, need to address alterations in isolation).

Alterations in D4 receptor

• Associated with increased novelty and sensation seeking (less behavioral inhibition)

DAT1 transporter and the DR4D receptor associated with

• associated with ADHD

• (These two parts of the brain are involved in controlling things like movement and attention.

• Since they affect different areas of the brain, it's important to study and understand changes in each one separately when looking at ADHD).