Genetics and Molecular Genetics

Biology

Standards: SC.912.L.14.6, SC.912.L.15.14, SC.912.L.15.15, SC.912.L.16.1, SC.912.L.16.2, HE.912.C.1.7

Textbook: Chapters 12 & 15

Chapter 12: Heredity-Mendelian Genetics

Essential Content

A. Law of Segregation and Independent Assortment (16.1)

1. Experiments

a. Formation of Gametes

b. Role of fertilization

c. Genes and alleles

d. Genotype vs. Phenotype

e. Generations: P, F1, F2

2. Mendel’s Principles

a. Principle of Dominance

b. Principle of Segregation

c. Principle of Independent Assortment

3. Dominant/Recessive Inheritance

B. Other Patterns of Inheritance (16.2)

1. Incomplete dominance

2. Codominance

3. Sex Linkage

4. Multiple Alleles

5. Polygenic Traits

6. Genes and Environment (14.6)

C. Punnett Squares (16.1)

1. Monohybrid Cross

2. Dihybrid Cross

D. Predict and Analyze Pedigrees (chapter 15)

1. Creation and Interpretation of Pedigrees

2. Karyotypes

3. Effects of genetics on health

Objectives

A. Analyze inheritance patterns caused by various modes of inheritance, including Mendel’s laws. (ALD)

B. Use Punnett Squares to express inheritance outcomes in percent, ratios and fractions.

Knowledge of patterns that include codominance, incomplete dominance, multiple alleles, sex-linkage, or polygenic inheritance of P and F1 generations is required.

C. Identify, analyze, and/or predict inheritance patterns caused by various modes of inheritance using pedigrees.

Vocabulary

genetics, probability, law of segregation, law of independent assortment, punnett square, trait, gene, allele, dominant, recessive, gamete, homozygous, heterozygous, phenotype, genotype, multiple allele, polygenic trait, complete dominance, incomplete dominance, codominance, sex-linked gene, nondisjunction, sex chromosome, karyotype, pedigree, autosome

Mendel and Experiment Results

. The scientific study of heredity is genetics. Gregor Mendel founded modern genetics with his experiments on a convenient model system, pea plants:

Fertilization is the process in which reproductive cells (egg from the female and sperm from the male) join to produce a new cell.

A trait is a specific characteristic, such as (in peas) seed color or plant height.

Mendel prevented self-pollination in the peas. He controlled fertilization so he could study how traits passed from one generation to the next.

He created hybrids, which are crosses between true-breeding parents (the P generation) with different traits.

· These hybrids were the F₁ (first filial) generation.

· They each showed the characteristic of only one parent.

Mendel found that traits are controlled by factors that pass from parent to offspring. Those factors are genes. The different forms of a gene are alleles.

Mendel’s principle of dominance states that some alleles are dominant and others are recessive. The recessive allele is exhibited only when the dominant allele is not present.

Segregation Mendel allowed members of the F₁ generation to self-pollinate. The trait controlled by the recessive allele appeared in the next generation (F₂) in about one-fourth of the offspring—even when it did not appear in the F₁ generation.

Separation of alleles is segregation.

When gametes (sex cells) form, alleles segregate so that each gamete carries only one allele for each gene.

The F₂ generation gets a new combination of alleles: one from each parent.

II. Mendel’s genetic revolution

A. Why Mendel succeeded:

1. Used a simple organism (pea plants) and one or two traits at a time

2. Started with pure-breeding (homozygous) plants

3. Obtained large numbers of offspring and analyzed using mathematics and probability

B. Mendel’s principles

1. Individuals have two alleles of each gene (same or different)

2. Law of segregation: gametes get only one allele of each gene

3. Genotype is genetic makeup

4. Phenotype is visible result of genotype; dominant allele determines phenotype if heterozygous

5. Law of independent assortment: alleles of two different genes behave independently

Punnet Squares and Probabilities

III. Applying Mendel’s principles

A. Monohybrid crosses

1. Starting with two pure-breeding parents, F1 offspring will be heterozygous

2. In F2 generation:

a. ¾ will show dominant trait (homozygous or heterozygous genotype)

b. ¼ will show recessive trait (homozygous recessive genotype)

B. Testcross

1. Cross an unknown individual with a homozygous recessive

2. Results of cross reveal genotype of unknown parent

C. Dihybrid crosses

1. 3:1 ratio for each gene

2. 9:3:3:1 ratio overall

Monohybrid Cross

Dihybrid Cross

Ch 12 Mendel Genetics.pdf

Chapter 15: What are genes and chromosomes?

15.1 and 15.2 Human chromosomes and genetic disorders (karyotypes).pdf

IV. Genes and chromosomes

1. Two homologous chromosomes carry the same genes but not necessarily the same alleles

2. Gametes get one allele of each gene because they get one chromosome from each pair

3. Genes located on different chromosomes behave independently in meiosis

Where are chromosomes found in a eukaryotic cell?

1. DNA double helix strand

2. DNA strand wrapped around histones (proteins in green color)

3. DNA with histones continued to be wrapped and coiled over and over

4. One single tightly wrapped and coiled DNA (blue) strand with a single centromere (red)

5. One chromosome with centromere (red)

Remember Meiosis......

Topic 18 Meiosis

Karyotypes (complete set of one humans chromosomes)

This individual is a male because they have both X and Y chromosomes. What would a female's karyotype look like?

A genome is the full set of all the genetic information that an organism carries in its DNA. Chromosomes are bundles of DNA and protein found in the nucleus of a eukaryotic cell. A karyotype is a picture that shows the complete diploid set of human chromosomes, grouped in pairs and arranged in order of decreasing size. A typical human diploid cell contains 46 chromosomes, or 23 pairs:

Two of the 46 are the sex chromosomes that determine an individual’s sex: XX = female and XY = male. The X chromosome carries nearly 10 times the number of genes as the Y chromosome.

The other 44 are autosomes, or autosomal chromosomes.

Pedigrees and heredity

Transmission of Human Traits Human genes follow the same Mendelian patterns of inheritance as the genes of other organisms:

Many human traits follow a pattern of simple dominance.

The alleles for many human genes display codominant inheritance.

Many human genes, including the genes for blood group, have multiple alleles.

A gene located on a sex chromosome is a sex-linked gene. The genes on sex chromosomes show a sex-linked pattern of inheritance, since females have two copies of many genes (located on X chromosomes) while males have just one.

In females, most of the genes in one of the X chromosomes are inactivated in each cell.

Human Pedigrees A chart used to analyze the pattern of inheritance that shows the relationships in a family is a pedigree. Pedigrees can be used to determine the nature of genes and alleles associated with inherited human traits.