Baker 2003/2004

Whose got Genes?

Genes, Heredity, & DNA

www.sciencequeen.net

Baker 2003/2004

What is GENETICS?

The study of how traits are inherited through the interactions of genes.

Baker 2003/2004

What are genes?Genes are a segment of DNA on a chromosome that controls a particular trait.

Genes are located on the chromosomes in the nuclei. Each organims has a fixed number of chromosomes.Humans have 23 pairs (46) chromosomes.Genetics is the study of how traits are passed on from one generation to another

                                  

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Define TRAIT

Ways of looking, thinking, or beingTraits that are genetic are passed down through the genes from parents to offspring

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Describe RECESSIVE

A trait that is covered over, or dominated, by another form of that trait and seems to disappear Hidden when the other copy of the gene contains the dominant allele.A recessive allele shows up only when there is no dominant allele presentShown with a lower-case letter

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Describe DOMINANT

A trait that covers over, or dominates, another form of that traitTrait that always shows up, even when only one of the two alleles is in the dominant form Shown by a capital letter

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Define GENOTYPE

An organism's genetic makeup

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Define PHENOTYPE

Outward physical appearance and behavior

of an organism

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What is a PUNNETT SQUARE?

Used to determine the likely hood that the offspring receives a certain trait.An uppercase letter stands for a dominant allele Lowercase letters stand for recessive alleles

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Punnett Squares

Sample Problem 1.   In roses, red flowers are dominant over white flowers. What are the possible offspring when a homozygous red rose is crossed with a homozygous white rose.

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Red rose = RR

white rose = rr

Generation 1 (I Do)R R

r

r

R

R

R

R

r r

r r

Genotype

4 Rr

Phenotype

100% Red Rose

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Red rose = Rr

white rose = rr

Generation 2 (We do)R r

r

r

R

R

r

r

r r

r r

Genotype

2 Rr 2 rr

Phenotype

50% Red 50% White

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Red rose = Rr

Red rose = Rr

Generation 3 (You do)

R r

R

r

R

R

r

r

RR

r r

Genotype

1 RR 2Rr 1 rr

Phenotype

75% Red 25% White

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Whose got Genes? Part 2

Genes, Heredity, & DNA

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Who was Gregor Mendel?

Austrian monk who studied mathematics and scienceAs a boy he could predict the possible types of flowers and fruits that would result from crossbreeding two plants in his father’s garden

Picture taken from biography.com

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Who was Gregor Mendel?

Curiosity about the connection between the color of a pea flower and the type of seed that same plant produced inspired him to begin experimenting with garden peas in 1856. Made careful use of scientific methods, which resulted in the first recorded study of how traits pass from one generation to the next.

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Define HEREDITY

The passing of traits from parent to

offspring

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Define ALLELE

The different forms of a trait that a gene may haveOne form of a gene

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What is HOMOZYGOUS?

Both alleles [forms of the gene] are the sameWhen offspring inherit two dominant genes, (one dominant gene from each parent) they are said to be homozygous dominantWhen offspring inherit two recessive genes, (one recessive gene from each parent) they are said to be homozygous recessive

AA

aa

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What is HETEROZYGOUS?

When alleles occur in different formsWhen offspring inherit one dominant gene and one recessive gene, they are said to be heterozygousSince the dominant gene will be expressed, they are said to be heterozygous dominant

Aa

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Generation 1

Heterozygous

Homozygous recessive

B Brown Eyes are Dominant to b Blue EyesB b

b

b

B

B

b

b

b b

b b

Genotype

2 Bb 2bb

Phenotype

50% Brown

50% Blue

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Generation 2 B Brown Eyes are Dominant to b Blue Eyes

Homozygous Dominant

Homozygous Recessive

B B

b

b

B

B

B

B

b b

b b

Genotype

4 Bb

Phenotype

100% Brown Eyes

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Generation 3B Brown Eyes are Dominant to b Blue Eyes

Homozygous Dominant

Heterozygous

B B

B

b

B

B

B

B

B B

b b

Genotype

2 BB 2 Bb

Phenotype

100% Brown Eyes

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References

Slideshow adapted from http://www.science-class.net/PowerPoints/Genetics.htm