Unit 5: Heredity

5.1

AP Classroom video notes:  Meiosis

Meiosis ensures the formation of haploid gametes cells in sexually reproducing diploid organisms.

Diploid 

• Two full sets, or pairs, of chromosomes 

• Chromosome pairs differ in size, shape, genetic information, centromere location

• The cell contains one set of each parent 

• Represented by 2n

• Body cells are diploid (e.g., skin cells, leaf cells, hypha cells)

Haploid 

• The cell contains one set of chromosomes 

• Represented by n

• Gametes, sex cells, are haploid (e.g., egg, pollen)

• Two haploid gamete cells come together in sexual reproduction to produce a diploid cell

Meiosis results in daughter cells with half the number of chromosomes as a parent cell

• The diploid parent cell produces four haploid daughter cells and sex cells.

Meiosis involves two rounds of a sequential series of steps (meiosis l and meiosis ll) 

• Two rounds of division

Phases of Meiosis 1 

Meiosis l 

Prophase l 

• The nuclear envelope begins to disappear

• Fibers begin to form

• DNA coils into visible duplicated (or double) chromosomes made up of sister chromatids

• Double chromosomes pair up based on size, shape, centromere location, genetic information 

• While paired, chromatids exchange genetic information with chromatids from the other chromosome (non-sister chromatids exchange genetic information)

Metaphase l 

• Double chromosomes remain in pairs 

• Fibers align pairs across the center of the cell membrane

Anaphase l 

• Fibers separate chromosome pairs 

• Each double chromosome, from the pair, migrates to opposite sides of the cell

Telophase 1

• The nuclear envelope reappears and establishes two separate nuclei 

• Each nucleus contains only one double chromosome from each pair

• The nucleus only contains half of the total information the parent nucleus contains.  

• Cytokinesis will separate the cell into two daughter cells 

• Daughter cells are haploid and genetically different from each other and the parent cell. 

Phases of Meiosis 2

Meiosis ll 

Prophase ll

• Nuclear envelope disappears

• Fibers begin to form 

Metaphase ll 

• Fibers align double chromosomes across the center of the cell

Anaphase ll

• Fibers separate sister chromatids

• Chromatids (single chromosomes) migrate to opposite poles

Telophase ll

• The nuclear envelope reappears and establishes separate nuclei 

• Each nucleus contains single chromosomes 

• Chromosomes will begin to uncoil

• Cytokinesis will separate the two cells into four daughter cells 

• Daughter cells are haploid and genetically different from each other 

Similarities between meiosis and mitosis

• Both processes go through the phases of mitosis ( Nuclear envelope disappearing, DNA coiling into chromosomes in the center, fibers to separate chromosomes, nuclear envelope reappearing, chromosomes uncoiling, followed by cytokinesis and production of daughter cells. 

Difference between mitosis and meiosis

• Mitosis produces two daughter cells that are genetically identical to the parent cell 

• Meiosis produces four haploid daughter cells that are genetically varied from each other and the parent cell. 

5.2

Ap Classroom video notes: Meiosis and Genetic Diversity

Meiosis generates genetic diversity 

• Meiosis results in four haploid gametes that are genetically varied 

• Certain processes take place during and after meiosis that generate genetic diversity

Crossing over increases genetic diversity among gametes

• Crossing over occurs in prophase 1 of meiosis 1 

• Nonsister chromatids of double homologous chromosomes exchange segments of chromosome

• Results in recombinant chromatids 

• The formation of recombinant chromatids increases genetic diversity

Homologous chromosomes- carry information for the same genes, one from each parent.

A random assortment of chromosomes serves to increase variation

• The order of the homologous pairs during metaphase 1 affects which chromosomes end up in each gamete

• Crossing over continues during metaphase 1

• Different combinations of chromosomes in each gamete increase genetic variation

Fertilization of gametes serves to increase variation

• When fertilization occurs, information from each parent contributes to the fertilized egg

• Typically one gamete from each parent fuse together to form a diploid offspring

• Fertilization is random in that any gamete can contribute to the diploid nature of genomes in offspring; this increases the potential for genetic variation/diversity  

5.3

Antiparallel: 

What is 5’ and 3’

“ Evolution: An organism adaptation over time”

Explain the inheritance of genes and traits as described by Mandel’s laws…

Essential knowledge

• Mendel’s laws of segregation and independent assortment can be applied to genes that are on different chromosomes

The law of segregation

• States that the two alleles for each trait segregate,  or separate, during the formation of gametes. During the formation of new zygotes, the alleles will combine at random with other alleles.

The law of Independent Assortment

• Describes how different genes independently separate from one another when reproductive cells develop.

Essential knowledge

• Fertilization involves the fusion of two haploid gametes, restoring the diploid number of chromosomes and increasing genetic variation. 

• Rules of probability can be applied to analyze the passage of single-gene traits from parent to offspring. 

5.4

5.5

Ap classroom video notes: Environmental effects on phenotype

Main Idea

• What is phenotypic plasticity?

• How can the same genotype result in multiple phenotypes?

• What effect do environmental conditions have on gene expression?

The same genotype can result in multiple phenotypes 

• Environmental factors can influence gene expression 

If the environmental conditions change, the expression of the gene can change

• Phenotypic plasticity is the ability of one genotype to produce more than one phenotype.

• Phenotypic diversity can be due to environmental factors and not necessarily due to genetic diversity 

Organisms can have the same genes but show different forms based on external factors

Example

Flower color based on soil pH

• In hydrangea plants; the color of the flower is determined by the pH of the soil 

• The same genes can yield different colored flowers depending on the environmental conditions. 

Acidic soil  (low pH); Blue or lavender flowers

Basic soil ( higher pH ): Pink or red flowers  

5.5

Ap classroom video notes: Environmental effects on phenotype

Main Idea

• What is phenotypic plasticity?

• How can the same genotype result in multiple phenotypes?

• What effect do environmental conditions have on gene expression?

The same genotype can result in multiple phenotypes 

• Environmental factors can influence gene expression 

If the environmental conditions change, the expression of the gene can change

• Phenotypic plasticity is the ability of one genotype to produce more than one phenotype.

• Phenotypic diversity can be due to environmental factors and not necessarily due to genetic diversity 

Organisms can have the same genes but show different forms based on external factors

Example

Flower color based on soil pH

• In hydrangea plants; the color of the flower is determined by the pH of the soil 

• The same genes can yield different colored flowers depending on the environmental conditions. 

Acidic soil  (low pH); Blue or lavender flowers

Basic soil ( higher pH ): Pink or red flowers  

5.6 

Ap Classroom video notes: Chromosomal inheritance pt. 1

Main Idea: 

• How does the law of segregation account for genetic variation? 

• How does independent assortment result in genetic variation?

• What is nondisjunction and how does it contribute to genetic variation? 

• How does fertilization in sexually reproducing organisms lead to genetic variation? 

• What effect does chromosomal inheritance have on genetic variation and human disorders?

5.6 

Ap Classroom video notes: Chromosomal inheritance pt.2

Main Idea: 

• How can chromosomal inheritance show patters if transmission of genes from parents to offspring

• How can human genetic disorders be based on chromosomal inheritance

• How can we use visual representations to analyze changes or disruptions in chromosomal inheritance

The chromosomal basis of inheritance provides an understanding of gene transmission. 

• Certain genetic disorders can be caused by a single mutated allele or a specific chromosomal change that is passed from parents to offspring

• Parent to offspring inheritance can be analyzed to determine patterns of gene transmission

• Mutations or mis-informations in gametes can result in disorders being present in offspring that were not present in parents. 

Example: huntingtons disease

• Huntingtons disease is a progressive and eventually fatal neurological disorder.

• Caused by single defective gene on chromosome 4 

• Inheritance is autosomal dominant  

This means that if you inherit the affected chromosome from a parent, you will get the disease.