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Genetics
Chapter 3, Section 1
Gregor Mendel is considered the “father” of modern genetics.
Studied pea plants.
Gregor Mendel
What is heredity?
the passing of traits from parents to offspring
Examples?
DNA
Genes are segments of DNA that control a trait.
Chromosomes are rod shaped structures made up of DNA – your chromosomes carry your genes.
Every human has 46 chromosomes (23 pairs) 23 from mom 23 from dad
So you have 2 copies of every gene.
Chromosomes
Different species of organisms have different numbers of chromosomes.
Ex. Cats – 38 Chickens – 78 Elephants – 56 Pineapple – 50 Shrimp – 86-92 Yeast - 32
Traits are physical characteristics.
Factors that control traits are called genes.
Genetics
The different forms of a gene are called alleles.
Each allele is represented by a letter in the genotype.
Bb
BB
bb
Alleles
Ex. of Alleles
Eye color: Let’s say there is one gene that
controls eye color - - - The different colors of eyes would
be the alleles for the gene. blue eye allele, green eye allele,
brown eye allele, etc.
An organism’s genotype is its genetic makeup. Genotype is shown with two letters.
Rr
HH tt
Bb
GGyy
Ss
Think of genotype as the actual genes that make the trait.Genotype
Alleles for a gene can be dominant or recessive.
Dominant alleles are always written with a capital letter.
Recessive alleles are always written with a lowercase letter.
HH
tt
GGyy
Ss
Genotype and Alleles
An organism’s phenotype is its physical appearance. Once you know which allele is dominant and which is recessive, you can figure out which trait will “show.”
Think of phenotype as what the gene
looks like.
If both alleles are the same, the organism is homozygous, or purebred, for that trait.
HHtt
GGyy
ss
Homozygous vs. Heterozygous
If the two alleles are different, the organism is heterozygous, or hybrid, for that trait.
Hh Tt
Bb
GgYy
Ss
Homozygous vs. Heterozygous
Were you paying attention???
1. Give an example of an allele.
2. K
3. r
4. JJ
5. Rr
6. bb
Were you paying attention???
1. Give an example of an allele.
2. dominant
3. recessive
4. Homozygous
dominant
5. heterozygous
6. Homozygous
recessive