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Inheritance – characteristics are passed through generations by genetic material (traits) Gregor Mendel - discovered the pattern of inheritance by studying

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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 codes for phenotype

• 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

3. A spotted owl (SS)

the genotype _____

the phenotype _____

SS

spotted

(Review)• Remember The

Principle of Segregation?

• Mendel learned that the alleles of each individual seperate and end up in gametes (meiosis)

• Ex. A female pure brown dog (bb)

b b

bb

PRACTICE

1. A hybrid male yellow canary (Yy)

 

Yy

2. A pure female white flower (rr)

rr

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

• Male red flower (Rr) • Female white flower

Rr

Sperm 1 Sperm 2

rr

Egg 1 Egg 2

+

+

+

+

=

=

=

=

1 1

1 2

2 1

2 2

Genotype Phenotype