unit 5: heredity

diploid cells

• two full sets/pairs of chromosomes

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

• cell contains one set from each parent

• represented by 2n

• ex. skin cells, leaf cells, hypha cell

haploid cells

• cell contains one set of chromosomes

• represented by n

• ex. gametes, sex cells

purpose of meiosis

ensures the formation of haploid gamete cells in sexually reproducing diploid organisms

results of meiosis

four genetically varied daughter cells with half the number of chromosomes as the parent cell

prophase I

• nuclear envelope begins to disappear 

• fibers begin to form

• DNA coils into visible duplicated 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 (nonsister chromatids exchange genetic information)

metaphase I

• double chromosomes remain in pairs

• fibers align pairs across the center of the cell

anaphase I

• fibers separate chromosome pairs

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

telophase I

• nuclear envelope reappears and establishes two separate nuclei

• each nucleus contains only one double chromosome from each pair

• nucleus only contains half of the total information the parent nucleus contained

• chromosomes will begin to uncoil

cytokinesis I

• separates the cell into two daughter cells

• daughter cells are haploid and genetically different from each other and the parent

prophase II

• nuclear envelope begins to disappear

• fibers begin to form

metaphase II

• fibers align double chromosomes across the center of the cell

anaphase II

• fibers separate sister chromatids

• chromatids (single chromosomes) migrate to opposite sides of the cell

telophase II

• nuclear envelope reappears and establishes separate nuclei

• each nucleus contains single chromosomes 

• chromosomes will begin to uncoil

cytokinesis II

• separates the two cells into four daughter cells

• daughter cells are haploid and genetically different from each other and parent cell

crossing over

• prophase I

• occurs when nonsister chromatids exchange segments

• results in recombinant chromosomes

random assortment of chromosomes

• metaphase I

• order of homologous pairs affect which chromosmes end up in each gamete

random fertilization

• information from each parent is contributed to the fertilized egg

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

• any gamete can contribute to the diploid nature of genomes in offspring

mendel’s law of segregation

• chromosomes carry alleles

• homologous chromosomes carry alleles for the same trait

• when chromosomes are separated into daughter cells during meiosis, the alleles for each trait are also separated

• separation of alleles allows for genetic variation among gametes

mendel’s law of independent assortment

• two or more genes assort independently of each other

• one trait is not automatically inherited with another trait

• alleles for separate traits can be packaged in every possible combination into gametes

gene

unit of heredity coding for a trait; they can be transferred from one generation to the next

trait

a genetically determined characteristic of an organism

allele

a specific variation of a gene; inherited from both parents

dominant allele

always shows in the phenotype if inherited

recessive allele

only shows in the phenotype when the dominant allele has not been inherited

genotype

combination of inherited alleles

homozygous

genotype containing two of the same alleles

heterozygous

genotype containing two different alleles

phenotype

the physical result or expression of the genotype

monohybrid cross

examination of how one trait is inherited

dihybrid cross

examination of how two traits are inherited

pedigree

a visual representation of tracing the history of a trait through familial generations

autosomal dominant trait

shows pattern of affected offspring with affected parents

autosomal recessive trait

shows pattern of affected offspring with unaffected parents

chi-square goodness-of-fit test

used to determine if the observed results are significantly varied from the expected results/ if there is a relationship between two groups of data

null hypothesis

states there is no relationship or no difference between two groups of data in an investigation

alternative hypothesis

states the observed results are due to a nonrandom cause

linked genes

genes that are adjacent and close to one another on the same chromosome and that are inherited together; less likely to be separated during crossing over

sex-linked traits

traits that are determined by genes located on sex chromosomes

map distance

• tells you how close together a pair of linked genes is

• determined by how frequently a pair of genes participates in a single crossover event 

non-nuclear inheritance occurs in ___ & ___

chloroplasts & mitochondria

traits from chloroplasts and mitochondrial DNA are ___ inherited

maternally

phenotypic plasticity

the ability of one genotype to produce more than one phenotype

cause of phenotypic plasticity

changes in environmental conditions

nondisjunction

the failure of chromosomes to fully separate during the formation of gamtes; results in too many or too few chromosomes in sex cells