Ch. 1 Mendel's Principles of Heredity

Gene

a region of DNA that encodes a protein or RNA, basic units of heredity

• underline formation of every heritable trait

  • Single Change = easy to study = EX: sickle cell anemia

  • Complex interactions = hair type, skin color, height

Heredity

the way that genes transmit traits from parents to offspring

Mendel

1st scientist to combine data collection, analysis, and theory to understand heredity = foundation of genetics

• apperance + disapperance of traits through numbers

Artificial Selection + problem

1st applied genetic technique, to control mating by choice of parents for the next generation

• Problem: results were unpredictable

The homunculus (misleading theory of inheritance)

Inherited features of offspring are contributed mainly by only one parent; many microscopists thought they saw a fully formed, miniature fetus in the sperm head

• Real: sperm cell is contributor to genetic info

Blended Inheritance (misleading theory of inheritance)

Parental traits become mixed and changed in the offspring

• Real: sometimes only one gene is visible (ex: skin color)

3 Critical Questions about selective breeding

1. What is inherited?

2. How is it inherited?

3. What is the role of chance in heredity?

Mendel’s paper/experiment

• “Experiments in plant hybrids” (1866)

• Pea plants used to see what traits would show up + how often it showed up

3 Benefits of using pea plants

1. The time between generations is relatively short

2. Can obtain large numbers of offspring in each generation

3. Antagonistic pairs: visibly different traits (white vs. purple flowers) rather than continuous traits (height, skin color)

Pure-breeding

the plant will always make more offspring identical to itself when self-fertilized over many generations

• Difference in one traits: seed color; 3:1 ratio

Alleles

Alternative forms of a single gene

• monohybrid: indiv w/ 2 diff alleles for single trait

• Dominant determines a functioning protein

Mendel’s 2 major results

1. Each hybrid resembles only one of the parents (disproved the blended inheritance theory)

2. Performed reciprocal crosses (switching traits of male and female parents) and observed the same results. (disproved the theory that traits were transmitted via a single parent)

Mendel’s law of segregation

The two alleles for each trait separate during gamete formation

Diploid Zygote (Yy)

Two gametes, one from each parent, unite at random at fertilization

Phenotype vs Genotype

Pheno: observable characteristic (e.g. yellow or green pea seeds)

Geno: a pair/composition of alleles in an individual (e.g. YY or Yy)

Mendel’s 2nd law (law of indep assortment)

alleles of different genes will segregate independently of each other during gamete formation

Mendel’s 3rd law (law of dominance)

The phenotype of a recessive allele is always masked by the dominant allele

What was Mendel’s pea color explanation

Y: encodes stay green enzyme (Sgr) to break down cholophyll

y: no Sgr = green pea

Reasons why determining inheritance pattern in humans is tricky (4)

1. Long generation time

2. Small numbers of progeny

3. No controlled matings

4. No pure-breeding lines

Most common single-gene traits from R alleles (5)

1. Thalassemia

2. Sickle-cell anemia

3. Cystic fibrosis

4. Tav-Sachs disease

5. Phenylketonuria

Most common single-gene traits from D alleles (2)

1. Hypercholoesterolemia

2. Huntington disease

Pedigree

orderly diagrams of a family's relevant genetic features

• Answers: is a trait determined by alt alleles for a single gene? Is trait D or R?

Vertical pattern of Inheritance

the transmission of genetic material from parent to offspring during reproduction

• EX: Huntington’s disease

Huntington’s disease

allele produces abnormal Htt proteindamages nerve cells, even when the normal protein is also present

Horizontal pattern of Inheritance

he movement of genetic material between organisms that are not parent and offspring (can be carriers)

• EX: cystic fibrosis

CFTR protein (cystic fibrosis)

protein regulates the passage of chloride ions across the cell membrane. Heterozygous individuals produce enough CFTR for normal lung function

3 key aspects of pedigrees with dominant traits

1. Affected children always have at least one affected parent

2. As a result, dominant traits show a vertical pattern of inheritance

3. Two affected parents can produce unaffected children, if both parents are heterozygotes

4 keys aspects of pedigrees with recessive traits

1. Affected individuals can be the children of two unaffected carriers, particularly as a result of consanguineous matings

2. All the children of two affected parents should be affected

3. Rare recessive traits show a horizontal pattern of inheritance

4. Recessive traits may show a vertical pattern of inheritance if the trait is extremely common in the population