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• Inheritance – characteristics are passed through generations by genetic material (traits)
Gregor Mendel - discovered the pattern of inheritance by studying pea plants.
How are characteristics passed down through generations?
How Do We Know?
The Principle of Segregation
1) Inherited traits are determined by distinct units named genes
2) Each gene carries two factors, one inherited from each parent (alleles)
3) The two alleles separate from each other and end up in gametes during meiosis.
What did Mendel discover?
NUCLEUS
CHROMOSOMES
GENES
ALLELES
SMALLEST size
DNA
Largest Size
Contains
Contains
Interaction between two
Made of
• In each of our cells (except or gametes) we have 23 pairs of chromosomes
• One member of the chromosome pair comes from our father, the other from our mother.
Largest Structure:
Karotype
• Genes are regions of DNA within the chromosome pair that code for a particular trait.
• Each gene is made up of two factors, one from each chromosome pair.
• These factors are called
alleles
How are genes arranged on chromosomes?
• The two alleles that make up each gene may be the same or different.
• If the alleles are the same they are called homozygous
• If the alleles are different
they are called heterozygous
Are an individual's alleles the same?
heterozygous
homozygous
• Each trait is determined by the interaction between the two alleles of a gene and several interactions are possible.
• The genetic make up of a trait= genotype
• The physical appearance of a trait= phenotype
How do alleles determine the trait of an individual?
1. Complete Dominance – when one allele completely masks the other.Dominant Alleles – only one allele needed to express trait.Recessive Alleles – need two recessive alleles for trait to be expressed.
Recessive trait : Sugary kernels are recessive
Genotype=
Phenotype=
Dominant trait:
Yellow kernels
Genotype=
Phenotype=
Ex: Y = yellow
y= sugary
2. Incomplete dominance
When the alleles are blended and the offspring have a mix of their parent traits.
ex. Snap Dragons
R = red
r = white
Offspring can be pink!
3. Codominance – in this case both alleles are expressed.
BB= black corn
YY= yellow corn
BY = black and yellow corn
Heterozygous genotype
• GENOTYPE - the two letters that represent the alleles of a gene
EX. RR, Rr, rr
• Phenotype - the outward appearance of an organism (what it looks like)
Ex. If a farmer has a red flower (RR)
- the genotype is RR
- the phenotype is red
1. A brown dog (bb)
the genotype ________
the phenotype _______
2. A long haired cat (Hh)
the genotype _______
the phenotype _______
bb
brown
Hh
Long haired
(Review)• Remember The
Principle of Segregation?
• Mendel learned that the alleles of each individual seperate and end up in gametes (meiosis)
If a male red flower (Rr) and a pure white flower from above got their gametes
together (fertilization )
what kind of combinations could be formed?
X