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