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)