Genetics Day 2

Life Science 7th GradeMs. Reekes

Recap from Monday

-Yesterday we learned about dominant and recessive alleles.

-What does dominant mean? - What does recessive mean?

- What are the 2 parts that compose DNA, and why is the structure of DNA important to it’s function.

DID YOU KNOW

If the total DNA in one person were laid in a straight line, it would stretch to the sun and back over 30 times (it’s 93 million miles from here to

the sun).

You could fit one thousand nuclei across the period at the end of this sentence.

DNA

• Where is your DNA stored? – LS2: DNA is what makes chromatin. Before cell

division chromatin condenses and creates chromatids.

– 2 chromatids create a chromosome

• Chromosomes spit during sexual reproduction and pair with another chromatid. – One chromosomes from your mother pairs with another chromosome from your father

» Similar to DNA phosphoric bases aligning.

Gregor Mendel.

• Gregor Mendel is the father of Genetics. • Gregor Mendel discovered dominant and

recessive traits when crossing pea plants. • He found that genes do not blend. Dominant

alleles are expressed or recessive alleles are expressed.

• Which is more likley to be expressed and why?

• http://www.youtube.com/watch?v=0vAAf4g5iF8

Alleles

An allele is an alternate form of a trait.-Brown and blonde hair are two different allelesDominant alleles: one who’s trait always shows up in the organism when the allele is present presentRecessive alleles: one who's trait is masked when a dominant allele is present• Alleles align from your mother and father on

the chromosomes in your body.

• You receive one allele from each parent for any given trait.

• The dominant allele will be expressed if it is present on the chromosome.

• The recessive allele will only be expressed if there are 2 recessive alleles.

Representations

• How do scientists represent a dominant or recessive trait

• Traits are represented by 2 letters.– Dominant traits are capitalized and recessive traits

are lower cased. • EXAMPLE: Lets look at eye alleles• Brown eyes: BB--- Dominant Homozygous• Green eyes: gg----- Recessive Homozygous.

• Visualize this cross by using a Punnet Square

• A Punnet Square: A chart used to determine possibilities from a genetic cross.

• - Lets do an example of Brown eyes crossing with green eyes. BB x GG

• Let do an example crossing brown hair with blonde hair. BB x ll

• Lets do an example crossing a brown mouse with a white mouse. BB x ww

Homozygous and Heterozygous

• Homo- Same• Hetero- Different • Zygous- Zygotic organisms (Sexual reproducing

organisms.) • Homozygous: Both alleles from both parents

are coding for the same trait. tt or TT• Heterozygous: The two alleles from each

parent are coding for different traits Tt

Answer on your own

• If two alleles are coding for different traits, which trait will be expressed?

Punnet Square Practice

• Cross dominant dark skin with recessive pale skin. DD x pp

• Cross heterozygous dark skin with homozygous recessive pale skin. Dd x pp

• Cross heterozygous dark skin with homozygous pale skin Dd xpp

Answer on your own

• It is not possible to be heterozygous for a trait. Why is that?

Homework

• Create a punnet square for your individual traits looking at your parents.

• Do a punnet square for at least 3 of your traits.

Refer to your dominant and recessive worksheet

• http://www.youtube.com/watch?v=_IOIx__UJ

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