Genes, traits, and this Genes, traits, and this guy named Mendelguy named Mendel

Biology Biology

Mr. DMr. D

MeiosisMeiosis

Before meiosis begins, the cell has __ Before meiosis begins, the cell has __ chromosomes or two sets of __chromosomes or two sets of __– 46 chromosomes46 chromosomes– 2 sets of 232 sets of 23

So, let us take for example, So, let us take for example, chromosome 5 codes for hair colorchromosome 5 codes for hair color

How many copies of chromosome 5 How many copies of chromosome 5 do we have?do we have?– 22

MeiosisMeiosis

Where did we get each chromosome?Where did we get each chromosome?– One from our momOne from our mom– One from our dadOne from our dad

Let’s pretend Chromosome 5 has the gene Let’s pretend Chromosome 5 has the gene for hair colorfor hair color

Let’s say that your mom blonde hair and Let’s say that your mom blonde hair and your dad has brown hairyour dad has brown hair

If I tell you that If I tell you that alleleallele means different means different form of a gene, how many forms of hair form of a gene, how many forms of hair color could you have?color could you have?– 22

GenesGenes

Let’s say your dad’s side of the family all Let’s say your dad’s side of the family all have brown hair.have brown hair.

Also, let’s say that all your mom’s side has Also, let’s say that all your mom’s side has blonde hair.blonde hair.

Therefore, your parent’s hair color is Therefore, your parent’s hair color is purebred (only one color ever appears in purebred (only one color ever appears in their family)their family)

What will the hair color be when they have What will the hair color be when they have a child?a child?– The child ends up with brown hair. So, which The child ends up with brown hair. So, which

alleleallele (different form of a gene) is (different form of a gene) is dominantdominant??– Which is Which is recessiverecessive??

GenesGenes

Now we know which allele for hair color is Now we know which allele for hair color is dominant (brown) and which is recessive dominant (brown) and which is recessive (blonde).(blonde).

DominantDominant alleles are capital letters like alleles are capital letters like “H”“H”

RecessiveRecessive alleles are small letters like “h”alleles are small letters like “h” How many How many forms of a geneforms of a gene do we have do we have

for each trait (ex. hair color)?for each trait (ex. hair color)? What are some possible combinations?What are some possible combinations?

Different combinationsDifferent combinations

Homozygous– genotype of identical alleles, ex. HH or hh

Heterozygous– genotype of different alleles, ex. Hh

So, how can we figure out the traits So, how can we figure out the traits passed on to each generation passed on to each generation (heredity)?(heredity)?

Now we can talk about Punnett squaresNow we can talk about Punnett squares

Gregor Mendel

Monastery of St. Thomas, Monastery of St. Thomas, Brno, Czech Republic.Brno, Czech Republic.

Taught physics and natural Taught physics and natural science.science.

Performed experiments 1856-Performed experiments 1856-1868, published in 1866.1868, published in 1866.

Used pea plantsUsed pea plants

How Mendel performed his crosses with pea plants

Fig. 8.5Fig. 8.5

Gregor Mendel

““I like to pea…I mean I like I like to pea…I mean I like pea plants”pea plants”

Why peas?Why peas?– Easy to growEasy to grow– Self-fertilize or can Self-fertilize or can

hybridize artificiallyhybridize artificially– Matures quicklyMatures quickly– Contrasting traits are easy Contrasting traits are easy

to seeto see

Mendel’s LawsMendel’s Laws

Law of dominanceLaw of dominance– Some alleles (variation) are dominant Some alleles (variation) are dominant

over other allelesover other alleles Law of segregationLaw of segregation

– Each gamete gets one copy of the geneEach gamete gets one copy of the gene Law of independent assortmentLaw of independent assortment

– Each trait separates independently Each trait separates independently during formation of gametesduring formation of gametes

Mendel’s 7 traits

1.2.3.

4.

5.

6.

7.

ProbabilityProbability

Sometimes we want to know how Sometimes we want to know how often something will occuroften something will occur

What is the chance of getting tails What is the chance of getting tails when you flip a coin?when you flip a coin?

How about 2 tails in a row?How about 2 tails in a row? For exampleFor example

Probability and punnett Probability and punnett squaressquares

Punnett squares can help us Punnett squares can help us determine genetic crossesdetermine genetic crosses

Punnett squarePunnett square

Predicts possible offspringsPredicts possible offsprings Capital letterCapital letter = dominant allele (ex. “H”) = dominant allele (ex. “H”) Lower case letterLower case letter = recessive allele (ex. = recessive allele (ex.

“h”)“h”) Same letter used for dominant/recessiveSame letter used for dominant/recessive

– HH, not HM, HL and so onHH, not HM, HL and so on ExpressedExpressed traits called traits called phenotypephenotype

– What you see/observeWhat you see/observe Genetic makeup =Genetic makeup = genotypegenotype

– The type of allelesThe type of alleles

O.J. Simpson capital murder case,1/95-9/95• Odds of blood in Ford Bronco not being R. Goldman’s:

• 6.5 billion to 1• Odds of blood on socks in bedroom not being N. Brown-Simpson’s:

• 8.5 billion to 1• Odds of blood on glove not being from R. Goldman, N. Brown-Simpson, and O.J. Simpson:

• 21.5 billion to 1• Number of people on planet earth:

• 6.1 billion• Odds of being struck by lightning in the U.S.:

• 2.8 million to 1• Odds of winning the Illinois Big Game lottery:

• 76 million to 1 • Odds of getting killed driving to the gas station to buy a lottery ticket

• 4.5 million to 1• Odds of seeing 3 albino deer at the same time:

• 85 million to 1• Odds of having quintuplets:

• 85 million to 1• Odds of being struck by a meteorite:

• 10 trillion to 1

Punnett SquarePunnett Square

This is a simple This is a simple Punnett square.Punnett square.

It looks like a It looks like a window panewindow pane

You put the alleles You put the alleles on the outsideon the outside

PP11 and F and F1 1 generationsgenerations It helps us figure out It helps us figure out

what offspring we what offspring we getget

HHHH

hh

hh

Cross the followingCross the following

Count the number of genotypes and Count the number of genotypes and phenotypesphenotypes– HH x hhHH x hh– HH x HhHH x Hh– Hh x HhHh x Hh– Rr x RrRr x Rr– Cross a heterozygous brown haired male Cross a heterozygous brown haired male

with a homozygous recessive blonde with a homozygous recessive blonde femalefemale