Mendel and Meiosis

Genes

segment of DNA that codes for a specific characteristic

ex: hair

Alleles

different versions of a gene, one dominant and one recessive

ex: brown or blond hair

principle of dominance

each gene has a dominant and recessive allele

• heterozygotes will show the dominant phenotype

principle of segregation

two alleles for a trait seperate into different gametes during meiosis 2

• each gamete cell created has a unique genetic makeup

principle of independent assortment

genes are passed from parent to offspring independently from other genes on the same chromosome

homozgous

have both recessive or both dominant alleles (AA, aa)

heterozygous

has one recessive allele and one dominant allele (Aa)

phenotype

physical characteristic of an organism

genotype

genetic makeup of an organism

incomplete dominance

• one allele for a specific trait is not completely expressed over its paired allele

• results in a 3rd phenotype where the physical trait is a combo of the phenotypes of both alleles

codominance

• two alleles of the same gene are expressed separatley to yield different traits in an individual

ex: green vs yellow alleles creates a heterozygous allele of green with yellow spots

multiple alleles

• involves more than two alleles that usually code for a certain characteristic in a species

• non-Mendelian inheritance pattern

ex: blood type

polygenic traits

• characteristic (height or skin color) that is influenced by two or more genes

• does not follow patterns of Mendelian inheritance

homologous chromosomes

• 2 matching chromosomes around same length, pattern, and position of the centromere

• one chromosome is from mother and one from father

diploid cell

• contains both homologous chromosomes

• found in somatic cells

haploid cell

contains only a single set of chromosomes

• found in gametes and created in meiosis

Meiosis I

• has 4 stages

1. Prophase I - each replicated chromosome pairs with its corresponding homologous chromosome

2. Metaphase I - paired homologous chromosomes line up across center of cell

3. Anaphase I - spindle fibers pull each homologous chromosome pair toward opposite ends of cell

4. Telophase I - nuclear membrane forms around each cluster of chromosomes

Meiosis II

• starts with Prophase II, theres 2 cells with 2 replicated chromosomes before this phase begins

1. Prophase II - neither cell goes through a round of chromosome replication. The cells each have 4 chromatids now

2. Metaphase II - chromosomes line up at middle of cell

3. Anaphase II - paired chromosomes seperate

4. Telophase II/Cytokenesis - end product is 4 daughter cells with hald the normal number of chromosomes

   

result of crossing over

• each gamete will have a different combo of alleles for the genes on the chromosome

• increases diversity

• ensures daughter cells have combo of DNA from both parents