Download Chapter 5: Heredity - Betsy Sanford`s Website

Basic Genetics
- the Study of Heredity Betsy Sanford
7th Life Science
Lost Mountain Middle School
• trait – are hereditary (passed from parent to
offspring through DNA)
• DNA – the chemical code for building
proteins
• proteins – create cell structure and function
• chromosomes – threadlike strands of DNA
• genes – sections of chromosomes that code
for specific proteins
• humans – about 20-25,000 genes on 46
chromosomes
DNA Diagrams
DNA Diagrams
DNA Diagrams
Human Chromosomes
• 23 pair = 46 total
• the last pair determines gender
Gregor Mendel: The Father of Genetics
• born 1822 in Austria
• college & monastery; worked in gardens
• wondered why similar plants had different
characteristics.
• decided to study pea plants because they grow
fast, are self-pollinating, and come in many
varieties.
• did not know about DNA; made his theories
based on the results of his experiments.
• in eight years (1856-1864), he grew over 30,000
pea plants
Gregor Mendel: The Father of Genetics
• cross-pollination - occurs when pollen from one
plant pollinates the egg of another plant
• true-breeding – when a plant self-pollinates and
always shows the same trait as the parent
• Mendel crossed true-breeding plants
Alleles
• the different forms of a gene
• flower color = purple or white
• purple flower color
– stronger, dominant
– represented with a capital letter
• white flower color
– recessive, weaker
– represented with a lower case letter
Mendel’s Pea Plants
Reginald Punnett
• English zoologist and
geneticist
• created a table that predicts
number and variety of
genetic possibilities in
offspring
• the Punnett square is still
used today in genetic
counseling
Punnett Square
• the letters
on the
inside of
the square
show the
possible
offspring
Genes
• you get genes from each parent
• each pair of genes is represented by a
two letter combination
• the letter combination shows the
possible alleles (forms) of the genes
• two capitals, PP
• two lower case pp
• or one capital and one lowercase Pp
• always write the capital letter first
Genotype
• the exact genetic make up of the
gene (the exact 2 alleles)
• represented by the letter
combinations
• PP, Pp, pp
Phenotype
•
•
•
•
•
•
the results of the genotype
what the letters show
what you can see of the trait
PP = purple flower color
Pp = purple flower color
pp = white flower color
Homozygous
• the alleles of a gene are exactly
the same
• PP = homozygous dominant
• pp = homozygous recessive
• also called purebred
Heterozygous
• the alleles of the gene are different
• Pp = heterozygous dominant
• also called hybrid