AP Bio: UNIT 5: Meiosis and Genetic Diversity

• Cell division for gamete formation

• Two rounds

haploid, diploid

4 genetically different haploid gametes

Nuclear membrane dissolves, chromosome condense and become visible, homologous chromosome pair and cross over

Chromosome align in single column as pairs in the middle

Sister chromatids separate to opposite sides of the cell, each have their own centromere

Two new nuclei, cytokinesis

Result: 2 diploid cells

Chromosomes condense and become visible

Chromosomes align in pairs

Sister chromatids separate to opposite sides and each have their own centromere

Cytokinesis, splits each of the two cell in half to result in 4 cells

• Formation of tetrads during prophase I by homologous chromosomes

• Crossing Over

• Increases genetic diversity

Genes that are closer together on the same chromosome tend to be inherited more often

• Switching of parts of chromosome

• Occur in the middle of a gene, can inactivate in

• Failure of chromosomes separating in anaphase I, resulting in daughter cells with abnormal number of chromosomes

• Example of a nondisjunction: Atypical number of chromosomes

  • Ex: Down Syndrome

DNA and RNA

genes on separate chromosomes not linked genes

• Organisms carry two variations of every trait (alleles), one from each parent

  • Alleles segregate, separate, independently into gametes, occurring during anaphase of meiosis

  • One allele for a trait ends up in each gamete and during fertilization the offspring have 2 alleles for a trait

• Genes for different traits segregate independently of one another

  • Occurs during metaphase I

Chart that illustrates inheritance of trait through generations

• Circles: Female

• Squares: Males

• Shaded Shapes: Have the trait

genetic makeup/alleles of trait

Physical expression of genotype

Two copies of same allele

Two different alleles

Only one copy of allele needed for trait to be expressed

Two copies of allele to be expressed

Both parents are heterozygous

Heterozygous for same two traits

P(A and B)= P(A) x P(B)

More space between 2 linked genes during prophase 1= more likely to cross over

Used to create maps that show distance between genes on chromosome

Measure in MAP UNITS

• 10 map units= 10% recomb frequ.

• Where most genes are

• Chromosomes that aren’t directly involved in sex-determination

Involved in sex determination, genes have different inheritance patterns than on autosomes

Females: Can express it, but it’s less likely

Males: More likely to have it expressed, because they only have one X-chromosome

Males with trait: All daughters will inherit it

Females with trait: Sons and Daughters each have 50% chance

Traits are produced by multiple genes to produce phenotype

• Ex: Height, Eye Color

Genes on mitochondrial and chloroplast DNA do not follow same inheritance patterns as nuclear DNA

• Eggs>sperm→more mtDNA and cpDNA in eggs

  • Maternal inheritance

  • Males with trait do not pass on to offspring

Sex-linked: Genes located on sex chromosome in nucleus and can be inherited from mother or father

Non-nuclear: Genes located in mitochondria or chloroplast and are inherited only from mother

• Phenotype=Genotype+Environment

• Genotypes ability to produce different phenotypes in response to environmental factors