1. Chapter 11: Introduction to Genetics Mendel and Meiosis

2. 11.1: Mendel’s Laws of Heredity
Gregor Mendel – Father of Genetics
genetics = branch of biology that studies heredity
traits = characteristics that are inherited
Mendel cross pollinated plants, studied one trait at a time
transferred gametes

3. Mendel’s Monohybrid Crosses
tall pea plant x short pea plant  tall plant
what happened to “shortness?”
tall offspring x tall offspring  ¾ tall, ¼ short

4. Mendel concluded that each organism has 2 factors for each of its traits
these are genes, located on chromosomes
different forms of genes = alleles
ex: plant may have 2 alleles for tallness
alleles are located on different copies of chromosomes – one from each parent

5. Principle of Dominance
dominant alleles – expressed whenever present
recessive alleles – only expressed if dominant is not present

6. Law of Segregation
alleles for each trait separate when gametes are formed
During fertilization, gametes randomly pair together

7. Phenotypes & Genotypes
phenotype = physical characteristics (observable)
genotypes = gene combination
homozygous – alleles are the same
ex: TT or tt
heterozygous – alleles are different
ex: Tt

8. Punnett Squares used to predict the possible genotypes of offspring
Assign letters (dominant = upper case, recessive = lower case)
Write out cross
Fill in Punnett square
Answer any questions

9. Mendels’s Dihybrid Crosses
dihybrid involves two traits
Mendel concluded that different traits are inherited independently of each other
= law of independent assortment
See Figure 11-8, pg 316

10. 11.4: Meiosis genes are found on chromosomes
1000+ genes on each chromosome

11. Diploid & Haploid Cells
number of chromosomes varies with each organism; is not related to complexity of organism
diploid – (2n): cell has 2 kinds of each chromosome
haploid – (n): cell with one of each chromosome

12. Homologous chromosomes
= paired chromosomes
have genes for the same traits arranged in same order
not identical to each other – can have different allele for same gene
see pg

13. Meiosis
meiosis produces cells with ½ the number of chromosomes as the parent
1 diploid (2n) cell  4 haploid (n) cells
haploid cells are gametes
male = sperm
female = eggs
combining egg & sperm  zygote

14. Phases of Meiosis