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Genetics
Chapter 11
Homologous Chromosomes
Half of an offspring’s chromosomes come from it’s mother
Half of it’s chromosomes come from it’s father
These chromosomes are considered homologous- each of the chromosomes from the father has a corresponding chromosome from the mother
ho·mol·o·gous (h -m l -g s, h -)adj.1. Corresponding or similar in position, value,
structure, or function.2. Biology Similar in structure and evolutionary
origin, though not necessarily in function, as the flippers of a seal and the hands of a human.
3. Genetics Having the same morphology and linear sequence of gene loci as another chromosome.5.
The American Heritage® Dictionary of the English Language, Fourth Edition copyright ©2000 by Houghton Mifflin Company.
Ploidy
A cell that contains both sets of homologous chromosomes is said to be diploid (2N)
A cell with only one set is called haploid (N) and is known as a sex cell ( ex. egg or sperm)
Meiosis
Mitosis
DNA Replication
Cell Division
Cell Division
Meiosis Mitosis
Outcomes
Gregor Mendel
Austrian monk sometimes known as the “father of genetics”
Experimented with pea plants that are self-pollinating so all genetic traits are identical between parent plant and seed
Used true-breeding plants-allowed to self-pollinate they produce identical offspring
Gregor Mendel b. 1822
Fertilization
During sexual reproduction, male and female reproductive cells join
Produces a new cell which has a mixture of the genetic information from the male and female parent cells
If self-fertilization happens offspring may be identical to parent
If fertilization from another individual takes place, genetic variations can occur
Cross Pollination
Test Subject: Pea Plant
Seed Shape Seed Color Seed Coat Color Pod Shape Pod Color Flower Position Plant Height
Cross Pollination
Mendel cut away the male pollen producing parts of pea plants and pollinated those plants with pollen from other flowers
This made it possible for Mendel to cross-breed plants with different traits and follow the patterns of occurrence
Genes and Dominance
Trait- a specific characteristic P – parental generation F1 – filial generation 1 (filial means
children) F2 – filial generation 2 (children of F1s,
could be called grandchildren) Hybrid – offspring of genetic crosses
Mendel Drew Two Conclusions
Conclusion 1 Biological inheritance is determined by
factors that are passed from one generation to the next
Today we call these factors genes The different forms of variation produced
by a gene are called alleles
Mendel Drew Two Conclusions
Conclusion 2 Mendel’s second conclusion is known
today as the principle of dominance Principle of Dominance states that some
alleles are dominant and others are recessive
Segregation
Segregation in the F1 Cross
Has the recessive allele disappeared or is it still present in the F1 plants?
Mendel allowed all seven types of F1 hybrids to produce an F2 generation (self pollinating)
Amazing! Results non-existent in the F1 generation reappear in 25% of F2
Segregation
The alleles separate or “segregate” during the formation of gametes (sex cells)
Offspring then have the possibility of inheriting two recessive genes, though they statistically get at least one dominant
Each gamete carries only one copy of the gene either the dominant OR the recessive, not both
Punnet Square
¾ of the offspring have purple phenotype
¼ of offspring have white phenotype
½ heterozygous ½ homozygous
(¼ recessive white, ¼ dominant purple)